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2020 Volume 36 Issue 10
2020, 36(10): 190703
doi: 10.3866/PKU.WHXB201907034
Abstract:
Miscibility between oil and supercritical carbon dioxide (scCO2) phases has attracted significant attention in the field of oil recovery because it can be utilized in miscible gas displacement of oil, achieving nearly 100% recovery efficiency. The high recovery efficiency of miscible CO2 flooding originates from the valuable heavy components of oil and CO2 gas phase forming a homogenous phase with high mobility in the oil-scCO2 miscible system. However, the high pressure required for oil-scCO2 miscibility is a nontrivial obstacle for practical applications of scCO2 flooding recovery. Therefore, it is important to develop assist-miscible agents to lower the necessary miscibility pressure. In oil and water systems, well-developed amphiphiles (such as surfactants) have shown great promise for reducing the interfacial tension and maintaining the stability of the emulsion system. Therefore, "oil-CO2 amphiphiles" that can assist the miscibility between oil and scCO2 have been proposed. Among potential oil-scCO2 amphiphiles, a series of polyester-based oil-CO2 amphiphiles with esters as the CO2-philic groups and long carbon chains as the oil-philic groups were prepared. The polyester-based oil-CO2 amphiphiles, acting as assist-miscible agents, showed great ability to lower the needed miscibility pressure. A visualized miscible method was used to examine the efficiency of the assist-miscible agents with white oil and kerosene as the oil phase. The height of the oil phase inside the chamber was measured through a glass window to monitor the miscibility with increasing CO2 pressure. When the height of the oil reached the top of chamber, the oil filled the entire space, indicating miscibility. Using this method, the following conclusions could be drawn: First, amphiphiles with more ester groups exhibited stronger CO2-philicity, providing stronger ability to dissolve carbon dioxide. Second, amphiphiles with hydrocarbon chain lengths of 16 carbons exhibited the optimal assist-miscible efficiency. Third, greater differences between the oil and scCO2 phase showed more obvious differentiation among amphiphiles, showing the leveling and differentiating effect of oil. The temperature range of 50–80 ℃ did not influence the assist-miscible efficiency of the polyester-based amphiphiles. The best miscibility-assisting performance was obtained with CAA8-X, which contains eight ester groups and a palmitic acid chain. CAA8-X at a concentration of 1% (w, mass fraction) lowered the miscibility pressure in the white oil-scCO2 system by 16.04%. Amphiphiles with polyether (PEO) groups also showed excellent assist-miscible efficiency. The findings presented herein extend the concept of "amphiphilicity" from oil-water phases to oil-scCO2 phases and have the potential to guide future studies regarding scCO2 flooding in actual CO2 flooding oil recovery. Moreover, for other two-phase systems, according to the general amphipathic law and particular system parameters, it should be possible to design the optimal "amphiphiles". ![]()
Miscibility between oil and supercritical carbon dioxide (scCO2) phases has attracted significant attention in the field of oil recovery because it can be utilized in miscible gas displacement of oil, achieving nearly 100% recovery efficiency. The high recovery efficiency of miscible CO2 flooding originates from the valuable heavy components of oil and CO2 gas phase forming a homogenous phase with high mobility in the oil-scCO2 miscible system. However, the high pressure required for oil-scCO2 miscibility is a nontrivial obstacle for practical applications of scCO2 flooding recovery. Therefore, it is important to develop assist-miscible agents to lower the necessary miscibility pressure. In oil and water systems, well-developed amphiphiles (such as surfactants) have shown great promise for reducing the interfacial tension and maintaining the stability of the emulsion system. Therefore, "oil-CO2 amphiphiles" that can assist the miscibility between oil and scCO2 have been proposed. Among potential oil-scCO2 amphiphiles, a series of polyester-based oil-CO2 amphiphiles with esters as the CO2-philic groups and long carbon chains as the oil-philic groups were prepared. The polyester-based oil-CO2 amphiphiles, acting as assist-miscible agents, showed great ability to lower the needed miscibility pressure. A visualized miscible method was used to examine the efficiency of the assist-miscible agents with white oil and kerosene as the oil phase. The height of the oil phase inside the chamber was measured through a glass window to monitor the miscibility with increasing CO2 pressure. When the height of the oil reached the top of chamber, the oil filled the entire space, indicating miscibility. Using this method, the following conclusions could be drawn: First, amphiphiles with more ester groups exhibited stronger CO2-philicity, providing stronger ability to dissolve carbon dioxide. Second, amphiphiles with hydrocarbon chain lengths of 16 carbons exhibited the optimal assist-miscible efficiency. Third, greater differences between the oil and scCO2 phase showed more obvious differentiation among amphiphiles, showing the leveling and differentiating effect of oil. The temperature range of 50–80 ℃ did not influence the assist-miscible efficiency of the polyester-based amphiphiles. The best miscibility-assisting performance was obtained with CAA8-X, which contains eight ester groups and a palmitic acid chain. CAA8-X at a concentration of 1% (w, mass fraction) lowered the miscibility pressure in the white oil-scCO2 system by 16.04%. Amphiphiles with polyether (PEO) groups also showed excellent assist-miscible efficiency. The findings presented herein extend the concept of "amphiphilicity" from oil-water phases to oil-scCO2 phases and have the potential to guide future studies regarding scCO2 flooding in actual CO2 flooding oil recovery. Moreover, for other two-phase systems, according to the general amphipathic law and particular system parameters, it should be possible to design the optimal "amphiphiles".
2020, 36(10): 191000
doi: 10.3866/PKU.WHXB201910001
Abstract:
The self-assembly of colloidal nanocrystals has emerged as a powerful strategy for the bottom-up fabrication of functional materials and nanodevices. Recently, the self-assembly of gold nanorods (GNRs) has attracted significant attention because of their unique plasmonic properties, but the realization of their adjustable self-assembly of GNRs through facile and effective approaches remains challenging. In this work, the controllable self-assembly of GNRs in aqueous solution was realized through the host-guest interactions of cyclodextrins (CDs) and the cetyltrimethylammonium bromide (CTAB) molecules adsorbed on the surface of the GNRs. The self-assembly of GNRs was readily achieved by the addition of aqueous α-CD solutions with varied concentrations into aqueous dispersions of CTAB-stabilized GNRs. At a relatively low α-CD concentration, slow aggregation of the GNRs occurred, resulting in their side-by-side assembly. This was revealed by the blue shift of the longitudinal surface plasmon resonance (LSPR) band in the absorption spectra and confirmed by transmission electron microscopy (TEM) observations. On the other hand, when a higher concentration of α-CD was added, fast aggregation of the GNRs occurred, resulting in their end-to-end assembly. This was revealed by the red shift in the LSPR band together with the TEM observations. If β-CD was employed instead of α-CD, the self-assembly of GNRs could also be induced, although a relatively higher concentration of β-CD was required to achieve the extent of aggregation similar to that induced by α-CD, indicating that the supramolecular host–guest interaction between CDs and the surfactant CTAB was crucial to the directed self-assembly of GNRs. Furthermore, the α-CD-induced assembly was inhibited on addition of excess CTAB, confirming that the supramolecular interaction of α-CD and CTAB played a key role in directing the self-assembly of the GNRs. Based on these experimental results, a possible mechanism for the α-CD-induced self-assembly of GNRs was proposed as follows: at a lower α-CD concentration, the gradual formation of the host-guest inclusion complex α-CD/CTAB led to the partial replacement of the highly charged CTAB bilayers adsorbed on the GNRs by the less charged complex, which resulted in a slow side-by-side assembly of the GNRs; at a higher α-CD concentration, the CTAB bilayers were quickly replaced by the α-CD/CTAB complex, and the CTAB molecules adsorbed at both ends of the GNRs were almost completely replaced, resulting in a fast end-to-end assembly of the GNRs. Additionally, on the basis of the hydrolysis of α-cyclodextrin catalyzed by α-amylase, the self-assembly of GNRs directed by the host-guest interaction could be used to realize the feasible detection of α-amylase in solutions. This self-assembly strategy mediated by the host-guest interaction may be extendable to other colloidal systems involving surfactants adsorbed on the surface of nanoparticles, and may open new avenues for the controllable self-assembly of non-spherical nanoparticles. ![]()
The self-assembly of colloidal nanocrystals has emerged as a powerful strategy for the bottom-up fabrication of functional materials and nanodevices. Recently, the self-assembly of gold nanorods (GNRs) has attracted significant attention because of their unique plasmonic properties, but the realization of their adjustable self-assembly of GNRs through facile and effective approaches remains challenging. In this work, the controllable self-assembly of GNRs in aqueous solution was realized through the host-guest interactions of cyclodextrins (CDs) and the cetyltrimethylammonium bromide (CTAB) molecules adsorbed on the surface of the GNRs. The self-assembly of GNRs was readily achieved by the addition of aqueous α-CD solutions with varied concentrations into aqueous dispersions of CTAB-stabilized GNRs. At a relatively low α-CD concentration, slow aggregation of the GNRs occurred, resulting in their side-by-side assembly. This was revealed by the blue shift of the longitudinal surface plasmon resonance (LSPR) band in the absorption spectra and confirmed by transmission electron microscopy (TEM) observations. On the other hand, when a higher concentration of α-CD was added, fast aggregation of the GNRs occurred, resulting in their end-to-end assembly. This was revealed by the red shift in the LSPR band together with the TEM observations. If β-CD was employed instead of α-CD, the self-assembly of GNRs could also be induced, although a relatively higher concentration of β-CD was required to achieve the extent of aggregation similar to that induced by α-CD, indicating that the supramolecular host–guest interaction between CDs and the surfactant CTAB was crucial to the directed self-assembly of GNRs. Furthermore, the α-CD-induced assembly was inhibited on addition of excess CTAB, confirming that the supramolecular interaction of α-CD and CTAB played a key role in directing the self-assembly of the GNRs. Based on these experimental results, a possible mechanism for the α-CD-induced self-assembly of GNRs was proposed as follows: at a lower α-CD concentration, the gradual formation of the host-guest inclusion complex α-CD/CTAB led to the partial replacement of the highly charged CTAB bilayers adsorbed on the GNRs by the less charged complex, which resulted in a slow side-by-side assembly of the GNRs; at a higher α-CD concentration, the CTAB bilayers were quickly replaced by the α-CD/CTAB complex, and the CTAB molecules adsorbed at both ends of the GNRs were almost completely replaced, resulting in a fast end-to-end assembly of the GNRs. Additionally, on the basis of the hydrolysis of α-cyclodextrin catalyzed by α-amylase, the self-assembly of GNRs directed by the host-guest interaction could be used to realize the feasible detection of α-amylase in solutions. This self-assembly strategy mediated by the host-guest interaction may be extendable to other colloidal systems involving surfactants adsorbed on the surface of nanoparticles, and may open new avenues for the controllable self-assembly of non-spherical nanoparticles.
2020, 36(10): 191003
doi: 10.3866/PKU.WHXB201910036
Abstract:
The regulation of supramolecular chirality has applications in various aspects including asymmetric catalysis, chiral sensing, optical materials and smart devices. Additionally, it provides opportunities for the simulation of important activities in living organisms and the clarification of their mechanisms. Herein, we synthesized a chiral gelator SQLG (styrylquinoxalinyl L-amino glutamic diamide) containing a π-conjugated headgroup by introducing the quinoxaline-derived moiety into L-glutamic diamide-based amphiphile via two simple condensation steps. SQLG self-assembled into nanofibers through multiple intermolecular interactions, including π–π stacking, hydrogen bonding and van der Waals interaction, leading to gelation of various organic solvents ranging from nonpolar to polar ones. Chirality transfer from the chiral center to the supramolecular level was observed when organogels formed, which manifested itself in circular dichroism (CD) spectra. The organogels formed in polar solvents such as N, N-dimethylformamide (DMF) and nonpolar solvents such as toluene exhibited opposite signals of supramolecular chirality, attributed to different hydrogen bonding strengths and thus two different types of gelator stacking modes of the gelators which was confirmed by infrared spectroscopy (IR) and X-ray diffraction (XRD). Circular polarized luminescence (CPL) denotes left-handed or right-handed circularly polarized light with different intensities emitted by the chiral luminescent system, and it characterizes the chirality of the excited state, which finds potential application in fields such as 3D optical displays, optical data storage, polarization-based information encryption and bioencoding. Owing to the strong fluorescence and supramolecular chirality, the toluene gel emitted right-handed circular polarized luminescence upon excitation, while the gel formed in DMF did not exhibit CPL emission because of its relatively weak fluorescence. Furthermore, the organogels responded rapidly and distinctly to the stimulus of acid due to the proton-accepting sites in the quinoxaline skeleton. Utilizing NMR spectroscopy, we found that the two nitrogen atoms in the quinoxaline moiety could be protonated upon acidification. During the process, intramolecular charge transfer (ICT) was significantly strengthened and the driving forces of self-assembly underwent remarkable changes, resulting in the collapse of the yellow transparent organogel into a red dispersion. Meanwhile, transformation from nanofibers to nanospheres was observed using a scanning electron microscope (SEM). With change in stacking modes in the supramolecular assembly, a complete inversion of the CD signal was detected. The CPL signal was found to be switched off, which along with the other changes of the system could subsequently be recovered by neutralization of the entire system. Therefore, we constructed a chiroptical switch with multiple stimuli-responsiveness through the introduction of an acid-sensitive π-conjugated moiety into the L-glutamic diamide-based chiral amphiphile. ![]()
The regulation of supramolecular chirality has applications in various aspects including asymmetric catalysis, chiral sensing, optical materials and smart devices. Additionally, it provides opportunities for the simulation of important activities in living organisms and the clarification of their mechanisms. Herein, we synthesized a chiral gelator SQLG (styrylquinoxalinyl L-amino glutamic diamide) containing a π-conjugated headgroup by introducing the quinoxaline-derived moiety into L-glutamic diamide-based amphiphile via two simple condensation steps. SQLG self-assembled into nanofibers through multiple intermolecular interactions, including π–π stacking, hydrogen bonding and van der Waals interaction, leading to gelation of various organic solvents ranging from nonpolar to polar ones. Chirality transfer from the chiral center to the supramolecular level was observed when organogels formed, which manifested itself in circular dichroism (CD) spectra. The organogels formed in polar solvents such as N, N-dimethylformamide (DMF) and nonpolar solvents such as toluene exhibited opposite signals of supramolecular chirality, attributed to different hydrogen bonding strengths and thus two different types of gelator stacking modes of the gelators which was confirmed by infrared spectroscopy (IR) and X-ray diffraction (XRD). Circular polarized luminescence (CPL) denotes left-handed or right-handed circularly polarized light with different intensities emitted by the chiral luminescent system, and it characterizes the chirality of the excited state, which finds potential application in fields such as 3D optical displays, optical data storage, polarization-based information encryption and bioencoding. Owing to the strong fluorescence and supramolecular chirality, the toluene gel emitted right-handed circular polarized luminescence upon excitation, while the gel formed in DMF did not exhibit CPL emission because of its relatively weak fluorescence. Furthermore, the organogels responded rapidly and distinctly to the stimulus of acid due to the proton-accepting sites in the quinoxaline skeleton. Utilizing NMR spectroscopy, we found that the two nitrogen atoms in the quinoxaline moiety could be protonated upon acidification. During the process, intramolecular charge transfer (ICT) was significantly strengthened and the driving forces of self-assembly underwent remarkable changes, resulting in the collapse of the yellow transparent organogel into a red dispersion. Meanwhile, transformation from nanofibers to nanospheres was observed using a scanning electron microscope (SEM). With change in stacking modes in the supramolecular assembly, a complete inversion of the CD signal was detected. The CPL signal was found to be switched off, which along with the other changes of the system could subsequently be recovered by neutralization of the entire system. Therefore, we constructed a chiroptical switch with multiple stimuli-responsiveness through the introduction of an acid-sensitive π-conjugated moiety into the L-glutamic diamide-based chiral amphiphile.
2020, 36(10): 190802
doi: 10.3866/PKU.WHXB201908025
Abstract:
Adlayer chemistry has been a significant subject of interest in physical chemistry over the past decades. Considerable attention has been paid to the development of high-performance film-based gas sensors, and tremendous progress has been achieved. Among the different analytical techniques, fluorescence provides a highly sensitive and selective method for detecting a wide variety of analytes. Film-based fluorescent sensors have emerged as one of the most promising candidates for chemical sensing and are being further developed into portable devices. Theoretically, relative signal changes including static and dynamic characteristics are significantly used to determine the sensing process; these characteristics are associated with surface absorption, the interaction between the analytes and sensing adlayer, as well as desorption kinetics in the absence and presence of the targeted gaseous analytes. As revealed earlier, there are a number of factors that determine the sensing behavior of a film, and the most important factors have been identified. Firstly, the suitability of the employed sensing fluorophore, which is important as it ultimately determines the effectiveness of a sensing process. Secondly, the structure of the fluorescent adlayer of the film; this is another important factor as it significantly determines the efficiency of mass transfer, which is necessary for efficient and reversible sensing. Finally, the chemical nature and surface structure of the substrate as these could affect the sensing performance of the film via the screening or enriching of analyte molecules. However, in situ, online, fast, and sensitive detection and discrimination of toxic and hazardous species via vapor sampling is a challenge that will persist for many years. By using the simultaneous interaction of multiple analytes with different sensing materials, the sensor array-based approach can recognize the overall change in the composition of complex mixtures, rather than just identifying their specific elements. The data-rich outputs of array-based sensing methods have recently been widely adopted by the analytical community due to their improved capabilities with statistical and cheminformatic approaches during analysis. Moreover, the community has recognized that numerous complex sensing challenges cannot be solved with conventional analytical tools. In the past 20 years, our group has been committed to effectively research the formation of fluorescent sensitive films, optimization of sensing films, and fabrication of film-based fluorescent sensor arrays. A series of fluorescence sensitive thin-film materials have been developed, and high-performance fluorescence sensors have been successfully fabricated due to which a positive technological transformation has been achieved. Based on the recent progress in our group, this article briefly reviews the key points of the interactions between the gaseous analytes and adlayer. Moreover, their applications have also been addressed in the vapor phase detection of explosives, illicit drugs, and volatile organic contaminants based on the film-based fluorescent gas sensors. Further discrimination of the complex analytes was realized using a sensor array and pattern recognition strategy. It is strongly believed that our studies are the first to provide powerful fluorescent techniques for the efficient detection and discrimination of important or hazardous substances with remarkably different properties. Meanwhile, the large-scale production of our development demonstrates that interdisciplinary corporation and industry participation plays a vital role in converting laboratory techniques to a conceptual sensing system, which can manufacture commercial portable detectors. Furthermore, we offer insights on the future directions and challenges of film-based sensors in gas sensing. ![]()
Adlayer chemistry has been a significant subject of interest in physical chemistry over the past decades. Considerable attention has been paid to the development of high-performance film-based gas sensors, and tremendous progress has been achieved. Among the different analytical techniques, fluorescence provides a highly sensitive and selective method for detecting a wide variety of analytes. Film-based fluorescent sensors have emerged as one of the most promising candidates for chemical sensing and are being further developed into portable devices. Theoretically, relative signal changes including static and dynamic characteristics are significantly used to determine the sensing process; these characteristics are associated with surface absorption, the interaction between the analytes and sensing adlayer, as well as desorption kinetics in the absence and presence of the targeted gaseous analytes. As revealed earlier, there are a number of factors that determine the sensing behavior of a film, and the most important factors have been identified. Firstly, the suitability of the employed sensing fluorophore, which is important as it ultimately determines the effectiveness of a sensing process. Secondly, the structure of the fluorescent adlayer of the film; this is another important factor as it significantly determines the efficiency of mass transfer, which is necessary for efficient and reversible sensing. Finally, the chemical nature and surface structure of the substrate as these could affect the sensing performance of the film via the screening or enriching of analyte molecules. However, in situ, online, fast, and sensitive detection and discrimination of toxic and hazardous species via vapor sampling is a challenge that will persist for many years. By using the simultaneous interaction of multiple analytes with different sensing materials, the sensor array-based approach can recognize the overall change in the composition of complex mixtures, rather than just identifying their specific elements. The data-rich outputs of array-based sensing methods have recently been widely adopted by the analytical community due to their improved capabilities with statistical and cheminformatic approaches during analysis. Moreover, the community has recognized that numerous complex sensing challenges cannot be solved with conventional analytical tools. In the past 20 years, our group has been committed to effectively research the formation of fluorescent sensitive films, optimization of sensing films, and fabrication of film-based fluorescent sensor arrays. A series of fluorescence sensitive thin-film materials have been developed, and high-performance fluorescence sensors have been successfully fabricated due to which a positive technological transformation has been achieved. Based on the recent progress in our group, this article briefly reviews the key points of the interactions between the gaseous analytes and adlayer. Moreover, their applications have also been addressed in the vapor phase detection of explosives, illicit drugs, and volatile organic contaminants based on the film-based fluorescent gas sensors. Further discrimination of the complex analytes was realized using a sensor array and pattern recognition strategy. It is strongly believed that our studies are the first to provide powerful fluorescent techniques for the efficient detection and discrimination of important or hazardous substances with remarkably different properties. Meanwhile, the large-scale production of our development demonstrates that interdisciplinary corporation and industry participation plays a vital role in converting laboratory techniques to a conceptual sensing system, which can manufacture commercial portable detectors. Furthermore, we offer insights on the future directions and challenges of film-based sensors in gas sensing.
2020, 36(10): 190904
doi: 10.3866/PKU.WHXB201909048
Abstract:
Peptide-based supramolecular colloids are assembled systems based on weak interactions between peptides (such as hydrogen bonding, electrostatic forces, hydrophobic effects, π–π interactions, and van der Waals forces), spontaneously formed in a bottom-up manner. Peptide-based supramolecular colloids have ordered molecular arrangements and regular structures, with characteristics of both traditional colloids and supramolecular systems. Constructing functional supramolecular colloids via weak intermolecular interactions assists in understanding the process of biomolecular self-assembly in vivo and provides an effective strategy for designing supramolecular materials with excellent performance. Peptides, consisting of several amino acids, are elegant building blocks in supramolecular chemistry as well as colloid and interface chemistry because of their biological origin, clear composition, low immunogenicity, structural programmability, excellent biosafety, and high biodegradability. Based on the approach of supramolecular self-assembly, peptides can be manipulated to form multiscale and multifunctional colloidal systems, which have widespread applications in medicine, catalysis, energy, nanotechnology, and other fields. However, the realization of precise control of the structures and functions of these supramolecular colloids through peptide design and intermolecular interactions regulation remains an important issue to be addressed. To study the assembly process and physicochemical mechanism of supramolecular colloids at the molecular scale, and to explore the relationship between colloidal structure and function, the construction and functionalization of supramolecular colloids must be achieved. This work is a systematic summary of the assembly mechanism, structures, and functions as well as the state of the art of peptide-based supramolecular colloids with emphasis on the regulation of intermolecular interactions and structure-function relationships. The research progress of peptide-based supramolecular colloids in the following fields is summarized herein: i) biomimetic photosynthesis, including light capture and charge separation; and ii) tumor phototherapies, including photothermal therapy (PTT) and photodynamic therapy (PDT). Currently, it is feasible to induce functional enhancement of peptide colloids via supramolecular assembly. The most important aspect is to design the primary structure of the peptide building block, to precisely control the weak interactions between peptide molecules and rationally optimize the self-assembly process, and control the size and structure of the assemblies. Follow-up studies should focus on the design of molecular precursors, the combination of basic research and practical application of peptide-based supramolecular colloids will be essential. The advantages of peptide-based supramolecular colloids, including their ordered organization, flexible structures, and versatile functions, will open up novel avenues for various applications of supramolecular colloids in fields such as green energy and medicine. It is hoped that this review will provide inspiration and broaden ideas to further drive the development and application of supramolecular colloids. ![]()
Peptide-based supramolecular colloids are assembled systems based on weak interactions between peptides (such as hydrogen bonding, electrostatic forces, hydrophobic effects, π–π interactions, and van der Waals forces), spontaneously formed in a bottom-up manner. Peptide-based supramolecular colloids have ordered molecular arrangements and regular structures, with characteristics of both traditional colloids and supramolecular systems. Constructing functional supramolecular colloids via weak intermolecular interactions assists in understanding the process of biomolecular self-assembly in vivo and provides an effective strategy for designing supramolecular materials with excellent performance. Peptides, consisting of several amino acids, are elegant building blocks in supramolecular chemistry as well as colloid and interface chemistry because of their biological origin, clear composition, low immunogenicity, structural programmability, excellent biosafety, and high biodegradability. Based on the approach of supramolecular self-assembly, peptides can be manipulated to form multiscale and multifunctional colloidal systems, which have widespread applications in medicine, catalysis, energy, nanotechnology, and other fields. However, the realization of precise control of the structures and functions of these supramolecular colloids through peptide design and intermolecular interactions regulation remains an important issue to be addressed. To study the assembly process and physicochemical mechanism of supramolecular colloids at the molecular scale, and to explore the relationship between colloidal structure and function, the construction and functionalization of supramolecular colloids must be achieved. This work is a systematic summary of the assembly mechanism, structures, and functions as well as the state of the art of peptide-based supramolecular colloids with emphasis on the regulation of intermolecular interactions and structure-function relationships. The research progress of peptide-based supramolecular colloids in the following fields is summarized herein: i) biomimetic photosynthesis, including light capture and charge separation; and ii) tumor phototherapies, including photothermal therapy (PTT) and photodynamic therapy (PDT). Currently, it is feasible to induce functional enhancement of peptide colloids via supramolecular assembly. The most important aspect is to design the primary structure of the peptide building block, to precisely control the weak interactions between peptide molecules and rationally optimize the self-assembly process, and control the size and structure of the assemblies. Follow-up studies should focus on the design of molecular precursors, the combination of basic research and practical application of peptide-based supramolecular colloids will be essential. The advantages of peptide-based supramolecular colloids, including their ordered organization, flexible structures, and versatile functions, will open up novel avenues for various applications of supramolecular colloids in fields such as green energy and medicine. It is hoped that this review will provide inspiration and broaden ideas to further drive the development and application of supramolecular colloids.
2020, 36(10): 190904
doi: 10.3866/PKU.WHXB201909046
Abstract:
In the last thirty years, Gemini surfactants with various structures have been designed, synthesized, and demonstrated to show superior physicochemical properties. However, the utilization of non-degradable surfactants, including these Gemini surfactants, poses a threat to the environment; hence, degradable Gemini surfactants are desirable. Herein, biodegradable cationic Gemini surfactants with amide or ester groups in the hydrophobic chains or the spacer were synthesized. A monomeric surfactant containing an amide group and a Gemini surfactant with amide groups both in the hydrophobic chains and the spacer were synthesized for comparison. The effects of amide group location on the aggregation behavior of Gemini surfactants were studied systematically. The differences between the Gemini surfactants with amide groups and Gemini surfactants with ester groups were evaluated by comparing their aggregation behavior and hydrogen bonding formation. The Gemini surfactants with amide groups (C12A-Cn-AC12) in the chains showed much larger exothermic ΔHmic and more negative ΔGmic values than those of the corresponding monomeric surfactant C12A; besides, their critical micelle concentration (cmc) was more than one order of magnitude lower than that of C12A. The amide groups located in the hydrophobic alkyl chains promoted hydrogen bonding formation and self-assembly of the Gemini surfactants C12A-Cn-AC12. Moreover, 1H NMR spectra revealed that the co-effect of a short spacer and hydrogen bonding leads to slow exchange of the C12A-C2-AC12 molecules between the monomer and the aggregate. For the Gemini surfactant series C12-ACnA-C12, the amide groups notably increased the spacer length, and largest cmc value and smallest exothermic ΔHmic value were observed for C12-AC2A-C12 instead of C12-AC6A-C12. In C12-AC12A-C12, the spacer was long and sufficiently flexible to adopt a "U"-shaped conformation above the cmc, and it acted as the hydrophobic part of the surfactant, as confirmed by 1H NMR spectra. Among the Gemini surfactant with amide groups in both the spacer and the hydrophobic alkyl chains, C12A-AC6A-AC12 had a smaller cmc and I1/I3 ratio as well as more exothermic ΔHmic values than those of C12A-C6-AC12 and C12-AC6A-C12. 1H NMR spectra indicated that an ester-alcohol structural equilibrium exists during aggregation for the Gemini surfactants with ester groups. In addition, the Gemini surfactants with ester groups formed water-mediated hydrogen bonds in the aggregates. This water-mediated hydrogen bonding between ester groups was weaker than the direct hydrogen bonding between amide groups. Therefore, the Gemini surfactants with ester groups, C12E-C6-EC12 and C12-EC6E-C12, exhibited lower surface activity, a larger micelle ionization degree, higher micropolarity, and smaller exothermic ΔHmic and less negative ΔGmic values than their counterparts with amide groups, C12A-C6-AC12 and C12-AC6A-C12. ![]()
In the last thirty years, Gemini surfactants with various structures have been designed, synthesized, and demonstrated to show superior physicochemical properties. However, the utilization of non-degradable surfactants, including these Gemini surfactants, poses a threat to the environment; hence, degradable Gemini surfactants are desirable. Herein, biodegradable cationic Gemini surfactants with amide or ester groups in the hydrophobic chains or the spacer were synthesized. A monomeric surfactant containing an amide group and a Gemini surfactant with amide groups both in the hydrophobic chains and the spacer were synthesized for comparison. The effects of amide group location on the aggregation behavior of Gemini surfactants were studied systematically. The differences between the Gemini surfactants with amide groups and Gemini surfactants with ester groups were evaluated by comparing their aggregation behavior and hydrogen bonding formation. The Gemini surfactants with amide groups (C12A-Cn-AC12) in the chains showed much larger exothermic ΔHmic and more negative ΔGmic values than those of the corresponding monomeric surfactant C12A; besides, their critical micelle concentration (cmc) was more than one order of magnitude lower than that of C12A. The amide groups located in the hydrophobic alkyl chains promoted hydrogen bonding formation and self-assembly of the Gemini surfactants C12A-Cn-AC12. Moreover, 1H NMR spectra revealed that the co-effect of a short spacer and hydrogen bonding leads to slow exchange of the C12A-C2-AC12 molecules between the monomer and the aggregate. For the Gemini surfactant series C12-ACnA-C12, the amide groups notably increased the spacer length, and largest cmc value and smallest exothermic ΔHmic value were observed for C12-AC2A-C12 instead of C12-AC6A-C12. In C12-AC12A-C12, the spacer was long and sufficiently flexible to adopt a "U"-shaped conformation above the cmc, and it acted as the hydrophobic part of the surfactant, as confirmed by 1H NMR spectra. Among the Gemini surfactant with amide groups in both the spacer and the hydrophobic alkyl chains, C12A-AC6A-AC12 had a smaller cmc and I1/I3 ratio as well as more exothermic ΔHmic values than those of C12A-C6-AC12 and C12-AC6A-C12. 1H NMR spectra indicated that an ester-alcohol structural equilibrium exists during aggregation for the Gemini surfactants with ester groups. In addition, the Gemini surfactants with ester groups formed water-mediated hydrogen bonds in the aggregates. This water-mediated hydrogen bonding between ester groups was weaker than the direct hydrogen bonding between amide groups. Therefore, the Gemini surfactants with ester groups, C12E-C6-EC12 and C12-EC6E-C12, exhibited lower surface activity, a larger micelle ionization degree, higher micropolarity, and smaller exothermic ΔHmic and less negative ΔGmic values than their counterparts with amide groups, C12A-C6-AC12 and C12-AC6A-C12.
2020, 36(10): 190904
doi: 10.3866/PKU.WHXB201909049
Abstract:
Wormlike micelles and low-molecular-weight hydrogels are composed of three-dimensional networks that endow them with viscoelasticity, but their viscoelastic properties are markedly different. The viscosity of wormlike micelles is attributed to a transient network, while that of gels is due to a stable network. Under certain conditions, wormlike micelles can undergo transition to gels with an increase in the density of the network. In our previous study, we found that the wormlike micelle formed by the ionic liquid-type surfactant 1-hexadecyl-3-octyl imidazolium bromide ([C16imC8]Br) without any additive has high viscoelasticity. The inclusion of a nonionic surfactant polyoxyethylene lauryl ether (Brij 30) is expected to enhance the viscoelasticity of [C16imC8]Br wormlike micelles via electrostatic shielding and strong hydrophobic interactions, which may be the driving factor for the wormlike micelle-to-gel structural transition. The morphology and viscoelasticity of [C16imC8]Br wormlike micelles with Brij 30 were studied as a function of concentration by rheological measurements and freeze-fracture transmission electron microscopy. The thermal stability and gel-sol transition temperature of the Brij 30/[C16imC8]Br gels were studied using rheology. The interaction between Brij 30 and [C16imC8]Br was studied by zeta potential measurements and nuclear magnetic resonance (NMR) spectroscopy. Upon the inclusion of Brij 30 into the [C16imC8]Br wormlike micelles, the viscoelasticity of the Brij 30/[C16imC8]Br samples first increased and then decreased with an increase in the Brij 30 concentration, at different initial concentrations of [C16imC8]Br. At a certain Brij 30 concentration, the Brij 30/[C16imC8]Br samples rheologically behaved as a gel. The maximum viscoelasticity of the [C16imC8]Br (4.06% (w))/Brij 30 gel was observed at a Brij 30/[C16imC8]Br molar ratio of 4.55. The viscoelasticity of the Brij 30/[C16imC8]Br gels was positively correlated with the activation energy of the gels. The gel-sol transition temperature of the Brij 30/[C16imC8]Br gels also increased first and then decreased with an increase in the Brij 30 concentration. The highest gel-sol transition temperature of the Brij 30/[C16imC8]Br (4.06% (w)) gel was observed at a Brij 30/[C16imC8]Br molar ratio of 2.93. The Brij 30 concentration had a notable impact on the viscoelasticity, thermal stability, and gel-sol transition temperature of the Brij 30/[C16imC8]Br gels. The zeta potential and 1H NMR measurements revealed that the neutral Brij 30 molecules are inserted into the palisade layer of the [C16imC8]Br wormlike micelles via hydrophobic interactions. This decreased the electrostatic repulsion between the [C16imC8]Br headgroups, which in turn induced the rapid growth of wormlike micelles and the formation of a stiffer network structure. Finally, the wormlike micelles underwent a structural transition to gels. The obtained results would aid in better understanding the relationship between wormlike micelles and gels, and may be of potential value for industrial and technological applications. ![]()
Wormlike micelles and low-molecular-weight hydrogels are composed of three-dimensional networks that endow them with viscoelasticity, but their viscoelastic properties are markedly different. The viscosity of wormlike micelles is attributed to a transient network, while that of gels is due to a stable network. Under certain conditions, wormlike micelles can undergo transition to gels with an increase in the density of the network. In our previous study, we found that the wormlike micelle formed by the ionic liquid-type surfactant 1-hexadecyl-3-octyl imidazolium bromide ([C16imC8]Br) without any additive has high viscoelasticity. The inclusion of a nonionic surfactant polyoxyethylene lauryl ether (Brij 30) is expected to enhance the viscoelasticity of [C16imC8]Br wormlike micelles via electrostatic shielding and strong hydrophobic interactions, which may be the driving factor for the wormlike micelle-to-gel structural transition. The morphology and viscoelasticity of [C16imC8]Br wormlike micelles with Brij 30 were studied as a function of concentration by rheological measurements and freeze-fracture transmission electron microscopy. The thermal stability and gel-sol transition temperature of the Brij 30/[C16imC8]Br gels were studied using rheology. The interaction between Brij 30 and [C16imC8]Br was studied by zeta potential measurements and nuclear magnetic resonance (NMR) spectroscopy. Upon the inclusion of Brij 30 into the [C16imC8]Br wormlike micelles, the viscoelasticity of the Brij 30/[C16imC8]Br samples first increased and then decreased with an increase in the Brij 30 concentration, at different initial concentrations of [C16imC8]Br. At a certain Brij 30 concentration, the Brij 30/[C16imC8]Br samples rheologically behaved as a gel. The maximum viscoelasticity of the [C16imC8]Br (4.06% (w))/Brij 30 gel was observed at a Brij 30/[C16imC8]Br molar ratio of 4.55. The viscoelasticity of the Brij 30/[C16imC8]Br gels was positively correlated with the activation energy of the gels. The gel-sol transition temperature of the Brij 30/[C16imC8]Br gels also increased first and then decreased with an increase in the Brij 30 concentration. The highest gel-sol transition temperature of the Brij 30/[C16imC8]Br (4.06% (w)) gel was observed at a Brij 30/[C16imC8]Br molar ratio of 2.93. The Brij 30 concentration had a notable impact on the viscoelasticity, thermal stability, and gel-sol transition temperature of the Brij 30/[C16imC8]Br gels. The zeta potential and 1H NMR measurements revealed that the neutral Brij 30 molecules are inserted into the palisade layer of the [C16imC8]Br wormlike micelles via hydrophobic interactions. This decreased the electrostatic repulsion between the [C16imC8]Br headgroups, which in turn induced the rapid growth of wormlike micelles and the formation of a stiffer network structure. Finally, the wormlike micelles underwent a structural transition to gels. The obtained results would aid in better understanding the relationship between wormlike micelles and gels, and may be of potential value for industrial and technological applications.
2020, 36(10): 191000
doi: 10.3866/PKU.WHXB201910004
Abstract:
In this work, light-responsive viscoelastic wormlike micelles based on cetyltrimethylammonium hydroxide (CTAOH) and cinnamic acid derivatives, including cinnamic acid (CA), 2-methoxycinnamic acid (2-MCA), 3-methoxycinnamic acid (3-MCA), 4-methoxycinnamic acid (4-MCA), 2, 3-dimethoxycinnamic acid (2, 3-DMCA), 2, 4-dimethoxycinnamic acid (2, 4-DMCA), 2, 3, 4-trimethoxycinnamic acid (2, 3, 4-DMCA), and 3, 4, 5-trimethoxycinnamic acid (3, 4, 5-DMCA), were prepared. The effects of the CA derivative structures, especially the position and number of methoxy moieties, on the formation of wormlike micelles were systematically determined. The CA derivatives facilitated the formation of long and entangled wormlike micelles. 1H NMR results showed that the CA derivatives participated in the formation of wormlike micelles via insertion of the aromatic moieties into the aggregates. The number of methoxy moieties had a much stronger effect on the viscosity of the wormlike micelle solution than the position of this moiety. The larger the number of methoxy moiety, the smaller was the aggregate. Substituted methoxy moieties increased the steric hindrance between the surfactants and CA molecules, thus hindering the formation of large aggregates. However, the position of the methoxy moiety had a predominant effect on the UV-light-induced transition of the wormlike micelles. Specifically, the ortho-methoxy moiety in the CA molecules dramatically enhanced the efficiency of UV-light-induced trans-cis isomerization. For example, the 2-MCA/CTAOH, 3-MCA/CTAOH, and 4-MCA/CTAOH binary systems (90 mmol·L-1/100 mmol·L-1) were gel-like with similar viscosities of around 20 Pa·s, but after UV light irradiation, they were transformed into a fluid with lower viscosity because of the formation of smaller aggregates. However, the irradiation time required for the transition varied significantly, as suggested by the results of viscosity measurements and UV-Vis spectroscopy. The 2-MCA/CTAOH system underwent complete phase transition within 3 h, whereas continuous transitions were observed for the 3-MCA/CTAOH and 4-MCA/CTAOH systems upon irradiation for 24 h. 1H NMR results suggested that the change in the configuration of MCA in the micelles before and after irradiation was the major cause of the abovementioned difference in the phase transition pattern. Initially, all the aromatic moieties of the trans-2-MCA molecules were deeply inserted into the hydrophobic cores of the micelles in a vertical manner, and the ionized carboxyl moiety was located in the palisade layer because of the electrostatic interactions between CTAOH and trans-2-MCA. In contrast, cis-2-MCA was inserted into the micelles in a horizontal manner, and some of the protons in the aromatic moiety were also transferred from the micellar core to the polar palisade layer. Accordingly, the CTAOH and cis-2-MCA molecules were packed loosely in the aggregates, thereby resulting in the formation of spherical micelles. Similar UV-light-induced transitions were observed for the 3-MCA/CTAOH and 4-MCA/CTAOH systems. ![]()
In this work, light-responsive viscoelastic wormlike micelles based on cetyltrimethylammonium hydroxide (CTAOH) and cinnamic acid derivatives, including cinnamic acid (CA), 2-methoxycinnamic acid (2-MCA), 3-methoxycinnamic acid (3-MCA), 4-methoxycinnamic acid (4-MCA), 2, 3-dimethoxycinnamic acid (2, 3-DMCA), 2, 4-dimethoxycinnamic acid (2, 4-DMCA), 2, 3, 4-trimethoxycinnamic acid (2, 3, 4-DMCA), and 3, 4, 5-trimethoxycinnamic acid (3, 4, 5-DMCA), were prepared. The effects of the CA derivative structures, especially the position and number of methoxy moieties, on the formation of wormlike micelles were systematically determined. The CA derivatives facilitated the formation of long and entangled wormlike micelles. 1H NMR results showed that the CA derivatives participated in the formation of wormlike micelles via insertion of the aromatic moieties into the aggregates. The number of methoxy moieties had a much stronger effect on the viscosity of the wormlike micelle solution than the position of this moiety. The larger the number of methoxy moiety, the smaller was the aggregate. Substituted methoxy moieties increased the steric hindrance between the surfactants and CA molecules, thus hindering the formation of large aggregates. However, the position of the methoxy moiety had a predominant effect on the UV-light-induced transition of the wormlike micelles. Specifically, the ortho-methoxy moiety in the CA molecules dramatically enhanced the efficiency of UV-light-induced trans-cis isomerization. For example, the 2-MCA/CTAOH, 3-MCA/CTAOH, and 4-MCA/CTAOH binary systems (90 mmol·L-1/100 mmol·L-1) were gel-like with similar viscosities of around 20 Pa·s, but after UV light irradiation, they were transformed into a fluid with lower viscosity because of the formation of smaller aggregates. However, the irradiation time required for the transition varied significantly, as suggested by the results of viscosity measurements and UV-Vis spectroscopy. The 2-MCA/CTAOH system underwent complete phase transition within 3 h, whereas continuous transitions were observed for the 3-MCA/CTAOH and 4-MCA/CTAOH systems upon irradiation for 24 h. 1H NMR results suggested that the change in the configuration of MCA in the micelles before and after irradiation was the major cause of the abovementioned difference in the phase transition pattern. Initially, all the aromatic moieties of the trans-2-MCA molecules were deeply inserted into the hydrophobic cores of the micelles in a vertical manner, and the ionized carboxyl moiety was located in the palisade layer because of the electrostatic interactions between CTAOH and trans-2-MCA. In contrast, cis-2-MCA was inserted into the micelles in a horizontal manner, and some of the protons in the aromatic moiety were also transferred from the micellar core to the polar palisade layer. Accordingly, the CTAOH and cis-2-MCA molecules were packed loosely in the aggregates, thereby resulting in the formation of spherical micelles. Similar UV-light-induced transitions were observed for the 3-MCA/CTAOH and 4-MCA/CTAOH systems.
2020, 36(10): 191000
doi: 10.3866/PKU.WHXB201910006
Abstract:
Separation and recycling of catalysts are crucial for realizing the objectives of sustainable and green chemistry but remain a great challenge, especially for enzyme biocatalysts. In this work, we report a new solvent-induced reversible inversion of Pickering emulsions stabilized by Janus mesosilica nanosheets (JMSNs), which is then utilized as a strategy for the in situ separation and recycling of enzymes. The interfacial active solid particle JMSNs is carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption experiments, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA).The JMSNs are demonstrated to show order-oriented mesochannels with a large specific surface area, and the hydrophobic octylgroup is selectively modified on one side of the nanosheets. Furthermore, the inversion is found to be a fast process that is strongly dependent on the interfacial activity of the solid emulsifier JMSNs. Such a phase inversion is also a general process that can be realized in various oil/water phasic systems, including ethyl acetate-water, octane-water, and cyclohexane-water systems. By carefully analyzing the capacity of JMSNs with different surface wettabilities for phase inversion, a triphase contact angle (θ) close to 90° and a critical oil-water ratio of 1 : 2 are identified as the key factors to achieve solvent-induced phase inversion via a catastrophic phase inversion mechanism. Importantly, this reversible phase inversion is suitable for the separation and recycling of enzyme biocatalysts that are sensitive to changes in the reaction medium. Specifically, during the reaction, the organic substrates are dissolved in the oil droplets and the water-soluble catalysts are dispersed in the water phase, while a majority of the product is released into the upper oil phase and the enzyme catalyst is confined inside the water droplets in the bottom layer after phase inversion. The perpendicular mesochannels of JMSNs provide a highly accessible reaction interface, and their excellent interfacial activity allows for more than 10 rounds of consecutive phase inversions by simply adjusting the ratio of oil to water in the system. Using the enzymatic hydrolysis kinetic resolution of racemic acetate as an example, our Pickering emulsion system shows not only a 3-fold enhanced activity but also excellent recyclability. Because no sensitive chemical reagents are used in this phase inversion process, the intrinsic activities of the catalysts can be preserved even after seven cycles. The current study provides an alternative strategy for the separation and recycling of enzymes, in addition to revealing a new innovative application for Janus-type nanoparticles. ![]()
Separation and recycling of catalysts are crucial for realizing the objectives of sustainable and green chemistry but remain a great challenge, especially for enzyme biocatalysts. In this work, we report a new solvent-induced reversible inversion of Pickering emulsions stabilized by Janus mesosilica nanosheets (JMSNs), which is then utilized as a strategy for the in situ separation and recycling of enzymes. The interfacial active solid particle JMSNs is carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption experiments, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric analysis (TGA).The JMSNs are demonstrated to show order-oriented mesochannels with a large specific surface area, and the hydrophobic octylgroup is selectively modified on one side of the nanosheets. Furthermore, the inversion is found to be a fast process that is strongly dependent on the interfacial activity of the solid emulsifier JMSNs. Such a phase inversion is also a general process that can be realized in various oil/water phasic systems, including ethyl acetate-water, octane-water, and cyclohexane-water systems. By carefully analyzing the capacity of JMSNs with different surface wettabilities for phase inversion, a triphase contact angle (θ) close to 90° and a critical oil-water ratio of 1 : 2 are identified as the key factors to achieve solvent-induced phase inversion via a catastrophic phase inversion mechanism. Importantly, this reversible phase inversion is suitable for the separation and recycling of enzyme biocatalysts that are sensitive to changes in the reaction medium. Specifically, during the reaction, the organic substrates are dissolved in the oil droplets and the water-soluble catalysts are dispersed in the water phase, while a majority of the product is released into the upper oil phase and the enzyme catalyst is confined inside the water droplets in the bottom layer after phase inversion. The perpendicular mesochannels of JMSNs provide a highly accessible reaction interface, and their excellent interfacial activity allows for more than 10 rounds of consecutive phase inversions by simply adjusting the ratio of oil to water in the system. Using the enzymatic hydrolysis kinetic resolution of racemic acetate as an example, our Pickering emulsion system shows not only a 3-fold enhanced activity but also excellent recyclability. Because no sensitive chemical reagents are used in this phase inversion process, the intrinsic activities of the catalysts can be preserved even after seven cycles. The current study provides an alternative strategy for the separation and recycling of enzymes, in addition to revealing a new innovative application for Janus-type nanoparticles.
2020, 36(10): 191000
doi: 10.3866/PKU.WHXB201910003
Abstract:
Marine organisms such as plants, algae or small animals can adhere to surfaces of materials that are submerged in ocean. The accumulation of these organisms on surfaces is a marine biofouling process that has considerable adverse effects. Marine biofouling on ship hulls can cause severe fuel consumption increase. Investigations on antifouling polymers are therefore becoming important research topics for marine vessel operations. Antifouling polymers can be applied as coating layers on the ship hull, protecting it against the settlement and growth of sea organisms. Polyethylene glycol (PEG) is a hydrophilic polymer that can effectively resist the accumulation of marine organisms. PEG-based antifouling coatings have therefore been extensively researched and developed. However, the inferior stability of PEG makes it subject to degradation, rendering it ineffective for long-term services. Zwitterionic polymers have also emerged as promising antifouling materials in recent years. These polymers consist of both positively charged and negatively charged functional groups. Various zwitterionic polymers have been demonstrated to exhibit exceptional antifouling properties. Previously, surface characterizations of zwitterionic polymers have revealed that strong surface hydration is critical for their antifouling properties. In addition to these hydrophilic polymers, amphiphilic materials have also been developed as potential antifouling coatings. Both hydrophobic and hydrophilic functional groups are incorporated into the backbones or sidechains of these polymers. It has been demonstrated that the antifouling performance can be enhanced by precisely controlling the sequence of the hydrophobic-hydrophilic functionalities. Since biofouling generally occurs at the outer surface of the coatings, the antifouling properties of these coatings are closely related to their surface characteristics in water. Therefore, understanding of the surface molecular structures of antifouling materials is imperative for their future developments. In this review, we will summarize our recent advancements of antifouling material surface analysis using sum frequency generation (SFG) vibrational spectroscopy. SFG is a surface-sensitive technique which can provide molecular information of water and polymer structures at interfaces in situ in real time. The antifouling polymers we will review include zwitterionic polymer brushes, mixed charged polymers, and amphiphilic polypeptoids. Interfacial hydration studies of these polymers by SFG will be presented. The salt effect on antifouling polymer surface hydration will also be discussed. In addition, the interactions between antifouling materials and protein molecules as well as algae will be reviewed. The above research clearly established strong correlations between strong surface hydration and good antifouling properties. It also demonstrated that SFG is a powerful technique to provide molecular level understanding of polymer antifouling mechanisms. ![]()
Marine organisms such as plants, algae or small animals can adhere to surfaces of materials that are submerged in ocean. The accumulation of these organisms on surfaces is a marine biofouling process that has considerable adverse effects. Marine biofouling on ship hulls can cause severe fuel consumption increase. Investigations on antifouling polymers are therefore becoming important research topics for marine vessel operations. Antifouling polymers can be applied as coating layers on the ship hull, protecting it against the settlement and growth of sea organisms. Polyethylene glycol (PEG) is a hydrophilic polymer that can effectively resist the accumulation of marine organisms. PEG-based antifouling coatings have therefore been extensively researched and developed. However, the inferior stability of PEG makes it subject to degradation, rendering it ineffective for long-term services. Zwitterionic polymers have also emerged as promising antifouling materials in recent years. These polymers consist of both positively charged and negatively charged functional groups. Various zwitterionic polymers have been demonstrated to exhibit exceptional antifouling properties. Previously, surface characterizations of zwitterionic polymers have revealed that strong surface hydration is critical for their antifouling properties. In addition to these hydrophilic polymers, amphiphilic materials have also been developed as potential antifouling coatings. Both hydrophobic and hydrophilic functional groups are incorporated into the backbones or sidechains of these polymers. It has been demonstrated that the antifouling performance can be enhanced by precisely controlling the sequence of the hydrophobic-hydrophilic functionalities. Since biofouling generally occurs at the outer surface of the coatings, the antifouling properties of these coatings are closely related to their surface characteristics in water. Therefore, understanding of the surface molecular structures of antifouling materials is imperative for their future developments. In this review, we will summarize our recent advancements of antifouling material surface analysis using sum frequency generation (SFG) vibrational spectroscopy. SFG is a surface-sensitive technique which can provide molecular information of water and polymer structures at interfaces in situ in real time. The antifouling polymers we will review include zwitterionic polymer brushes, mixed charged polymers, and amphiphilic polypeptoids. Interfacial hydration studies of these polymers by SFG will be presented. The salt effect on antifouling polymer surface hydration will also be discussed. In addition, the interactions between antifouling materials and protein molecules as well as algae will be reviewed. The above research clearly established strong correlations between strong surface hydration and good antifouling properties. It also demonstrated that SFG is a powerful technique to provide molecular level understanding of polymer antifouling mechanisms.
2020, 36(10): 191000
doi: 10.3866/PKU.WHXB201910005
Abstract:
Particle-stabilized dispersions such as emulsions, foams and bubbles are catching increasing attentions across a number of research areas. The adsorption mechanism and role of these colloidal particles in stabilizing the oil-water or gas-water interfaces and how these particles interact at interfaces are vital to the practical use of these dispersion systems. Although there have been intensive investigations, problems associated with the stabilization mechanisms and particle-particle interactions at interfaces still remain to explore. In this paper, we first systematically review the historical understanding of particle-stabilized emulsions or bubbles and then give an overview of the most important and well-established progress in the understanding of particle-stabilized systems, including emulsions, foams and liquid marbles. The particle-adsorption phenomena have long been realized and been discussed in academic paper for more than one century and a quantitative model was proposed in the early 1980s. The theory can successfully explain the adsorption of solid particles onto interface from energy reduction approaches. The stability of emulsions and foams can be readily correlated to the wettability of the particles towards the two phases. And extensive researches on emulsion stability and various strategies have been developed to prepared dispersion systems with a certain trigger such as pH and temperature. After that, we discuss recent development of the interactions between particles when they are trapped at the interface and highlight open questions in this field. There exists a huge gap between theoretical approaches and experimental results on the interactions of particles adsorbed at interfaces due to demanding experimental devices and skills. In practice, it is customary to use flat surfaces/interfaces as model surfaces to investigate the particle-particle at interfaces although most of the time interfaces are produced with a certain curvature. It is shown that the introduction of particles onto interfaces can generate charges at the interfaces which could possibly account for the long range electrostatic interactions. Finally, we illustrate that particle-stabilized dispersions have been found wide applications in many fields and applications such as microcapsules, food, biomedical carriers, and dry water. One of the most investigated areas is the microencapsulation of actives based on Pickering emulsion templates. The particles adsorbed at the interface can serve as interfacial stabilizers as well as constituting components of shells of colloidal microcapsules. Emulsions stabilized by solid particles derived from natural and bio-related sources are promising platforms to be applied in food related industries. Emulsion systems stabilized by solid particles of the w/w (water-in-water) feature are discussed. This special type of emulsion is attracting increasing attentions due to their all water features. Besides of oil-water interface, particle stabilized air-water interface share similar stabilization mechanism and several applications reported in the literature are subsequently discussed. We hope that this paper can encourage more scientists to engage in the studies of particle-stabilized interfaces and more novel applications can be proposed based on this mechanism ![]()
Particle-stabilized dispersions such as emulsions, foams and bubbles are catching increasing attentions across a number of research areas. The adsorption mechanism and role of these colloidal particles in stabilizing the oil-water or gas-water interfaces and how these particles interact at interfaces are vital to the practical use of these dispersion systems. Although there have been intensive investigations, problems associated with the stabilization mechanisms and particle-particle interactions at interfaces still remain to explore. In this paper, we first systematically review the historical understanding of particle-stabilized emulsions or bubbles and then give an overview of the most important and well-established progress in the understanding of particle-stabilized systems, including emulsions, foams and liquid marbles. The particle-adsorption phenomena have long been realized and been discussed in academic paper for more than one century and a quantitative model was proposed in the early 1980s. The theory can successfully explain the adsorption of solid particles onto interface from energy reduction approaches. The stability of emulsions and foams can be readily correlated to the wettability of the particles towards the two phases. And extensive researches on emulsion stability and various strategies have been developed to prepared dispersion systems with a certain trigger such as pH and temperature. After that, we discuss recent development of the interactions between particles when they are trapped at the interface and highlight open questions in this field. There exists a huge gap between theoretical approaches and experimental results on the interactions of particles adsorbed at interfaces due to demanding experimental devices and skills. In practice, it is customary to use flat surfaces/interfaces as model surfaces to investigate the particle-particle at interfaces although most of the time interfaces are produced with a certain curvature. It is shown that the introduction of particles onto interfaces can generate charges at the interfaces which could possibly account for the long range electrostatic interactions. Finally, we illustrate that particle-stabilized dispersions have been found wide applications in many fields and applications such as microcapsules, food, biomedical carriers, and dry water. One of the most investigated areas is the microencapsulation of actives based on Pickering emulsion templates. The particles adsorbed at the interface can serve as interfacial stabilizers as well as constituting components of shells of colloidal microcapsules. Emulsions stabilized by solid particles derived from natural and bio-related sources are promising platforms to be applied in food related industries. Emulsion systems stabilized by solid particles of the w/w (water-in-water) feature are discussed. This special type of emulsion is attracting increasing attentions due to their all water features. Besides of oil-water interface, particle stabilized air-water interface share similar stabilization mechanism and several applications reported in the literature are subsequently discussed. We hope that this paper can encourage more scientists to engage in the studies of particle-stabilized interfaces and more novel applications can be proposed based on this mechanism
2020, 36(10): 191000
doi: 10.3866/PKU.WHXB201910007
Abstract:
Liquid marbles (LMs) are liquid droplets coated with a layer of lyophobic particles at the air-liquid interface. Since the pioneering work by Aussillous et al. in 2001, LMs have attracted significant attention owing to their facile fabrication, flexibility in the choice of the constituent particles and liquids, intriguing properties such as non-wetting and non-adhesive nature, satisfactory elasticity and stability, as well as promising applications in microfluidics, sensors, controlled release, and microreactors. The classical strategy for the preparation of LMs involves rolling a small volume of a droplet on a lyophobic powder bed for complete encapsulation of the liquid by the particles. In addition, various innovative methods, including electrostatic and coalescent approaches, have been developed for preparing special LMs with a complicated structure or morphology. Diverse materials such as water, surfactant solutions, liquid metals, reagents, blood, and even viscous adhesives have been employed as the internal liquid for the fabrication of LMs. Theoretically, any particulates such as lycopodium, polytetrafluoroethylene, Fe3O4, SiO2, and graphite grains can be employed as the outer coating, but they are usually required to be lyophobic with sizes of less than hundreds of microns. The unique structure of the particle-covered droplet and the dual solid-liquid characteristics endow LMs with some unique and interesting properties, especially the non-wetting and non-adhesive nature. As the lyophobic coating particles restrain the internal liquid from contacting the substrate, LMs can move easily across either solid or liquid surfaces, neither wetting the substrate nor contaminating the internal liquid. An equally fascinating property of LMs is their satisfactory stability, which is necessary for most of their applications. The high stability of LMs stems from the protection of the coating powders and is embodied in both good mechanical stability (remaining intact after being released from a certain height or under a certain compression) and long lifetime (greatly suppressing the evaporation of the internal liquid). These extraordinary properties make LMs promising candidates for use in multitudinous fields, especially droplet microfluidics and microreactors. The potential application of LMs in microfluidics is ascribed to their non-wetting, non-adhesive nature and other features such as an ability to float on a liquid surface, coalescence, split, a small force of rolling friction, and response to external forces. Notably, LMs hold great promise for applications in microreactions, because they can create a confined reaction microenvironment, minimize reagent usage, facilitate unhindered gas exchange between the internal liquid medium and the surrounding environment, and allow the entry/exit of the reactants/products. We herein review the recent advances in LMs, such as manufacturing techniques, formation mechanisms, physical properties, and emerging applications. In particular, much attention is paid to the factors affecting the stability of LMs and the potential strategies to increase their stability. Moreover, this review discusses the challenges in the future development of LMs, suggests several possible ways of addressing these challenges, and forecasts the future development directions. We believe that this review can help researchers gain a better understanding of LMs and promote their further advances. ![]()
Liquid marbles (LMs) are liquid droplets coated with a layer of lyophobic particles at the air-liquid interface. Since the pioneering work by Aussillous et al. in 2001, LMs have attracted significant attention owing to their facile fabrication, flexibility in the choice of the constituent particles and liquids, intriguing properties such as non-wetting and non-adhesive nature, satisfactory elasticity and stability, as well as promising applications in microfluidics, sensors, controlled release, and microreactors. The classical strategy for the preparation of LMs involves rolling a small volume of a droplet on a lyophobic powder bed for complete encapsulation of the liquid by the particles. In addition, various innovative methods, including electrostatic and coalescent approaches, have been developed for preparing special LMs with a complicated structure or morphology. Diverse materials such as water, surfactant solutions, liquid metals, reagents, blood, and even viscous adhesives have been employed as the internal liquid for the fabrication of LMs. Theoretically, any particulates such as lycopodium, polytetrafluoroethylene, Fe3O4, SiO2, and graphite grains can be employed as the outer coating, but they are usually required to be lyophobic with sizes of less than hundreds of microns. The unique structure of the particle-covered droplet and the dual solid-liquid characteristics endow LMs with some unique and interesting properties, especially the non-wetting and non-adhesive nature. As the lyophobic coating particles restrain the internal liquid from contacting the substrate, LMs can move easily across either solid or liquid surfaces, neither wetting the substrate nor contaminating the internal liquid. An equally fascinating property of LMs is their satisfactory stability, which is necessary for most of their applications. The high stability of LMs stems from the protection of the coating powders and is embodied in both good mechanical stability (remaining intact after being released from a certain height or under a certain compression) and long lifetime (greatly suppressing the evaporation of the internal liquid). These extraordinary properties make LMs promising candidates for use in multitudinous fields, especially droplet microfluidics and microreactors. The potential application of LMs in microfluidics is ascribed to their non-wetting, non-adhesive nature and other features such as an ability to float on a liquid surface, coalescence, split, a small force of rolling friction, and response to external forces. Notably, LMs hold great promise for applications in microreactions, because they can create a confined reaction microenvironment, minimize reagent usage, facilitate unhindered gas exchange between the internal liquid medium and the surrounding environment, and allow the entry/exit of the reactants/products. We herein review the recent advances in LMs, such as manufacturing techniques, formation mechanisms, physical properties, and emerging applications. In particular, much attention is paid to the factors affecting the stability of LMs and the potential strategies to increase their stability. Moreover, this review discusses the challenges in the future development of LMs, suggests several possible ways of addressing these challenges, and forecasts the future development directions. We believe that this review can help researchers gain a better understanding of LMs and promote their further advances.
2020, 36(10): 200103
doi: 10.3866/PKU.WHXB202001037
Abstract:
2020, 36(10): 200307
doi: 10.3866/PKU.WHXB202003073
Abstract:
2020, 36(10): 200400
doi: 10.3866/PKU.WHXB202004004
Abstract:
2020, 36(10): 200402
doi: 10.3866/PKU.WHXB202004021
Abstract:
2020, 36(10): 200403
doi: 10.3866/PKU.WHXB202004031
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2020, 36(10): 200407
doi: 10.3866/PKU.WHXB202004078
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2020, 36(10): 200505
doi: 10.3866/PKU.WHXB202005053
Abstract:
