Login In
2019 Volume 37 Issue 6
2019, 37(6): 535-547
doi: 10.1007/s10118-019-2245-9
Abstract:
Graphene fibers are a kind of novel carbon fibers assembled by orderly aligned graphene sheets with high flexibility, good conductivity, high thermal conductivity, and low density, which make them possible to be widely used in high-performance and multi-functional compound materials as well as flexible electronic devices. In this review, we summarize the research progress in the synthesis of graphene fibers, and their applications in sensor, energy storage, and energy conversion. Furthermore, the current issues and some prospects for the future trend of graphene fibers are discussed.
Graphene fibers are a kind of novel carbon fibers assembled by orderly aligned graphene sheets with high flexibility, good conductivity, high thermal conductivity, and low density, which make them possible to be widely used in high-performance and multi-functional compound materials as well as flexible electronic devices. In this review, we summarize the research progress in the synthesis of graphene fibers, and their applications in sensor, energy storage, and energy conversion. Furthermore, the current issues and some prospects for the future trend of graphene fibers are discussed.
2019, 37(6): 548-559
doi: 10.1007/s10118-019-2212-5
Abstract:
Bacterial infection is a very troublesome issue in wound treatment, which stimulates exudate formation and severely delays the healing process. Herein, a thermogelling dressing system composed of two triblock copolymers of poly(D,L-lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(D,L-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) with different block lengths was developed to deliver teicoplanin (TPN), a glycopeptide antibiotic, for cutaneous wound repair. The TPN-loaded thermogel was a free-flowing sol at room temperature and formed a semi-solid gel at physiological temperature. In vitro studies demonstrated that the TPN-loaded thermogel system exhibited desired tissue adhesiveness and realized the sustained release of TPN in a fast-followed-slow manner for over three weeks. Furthermore, a full-thickness excision wound model in Sprague-Dawley (SD) rats was constructed to assess the efficacy of TPN-loaded thermogel formulation. Gross and histopathologic observations implied that treatment with the thermogel formulation reduced inflammation response, promoted disposition of collagen, enhanced angiogenesis, and accelerated wound closure and maturity of SD rats. The combination of the bioactivity of TPN and the acidic nature of the thermogel matrix was responsible for such an enhanced wound healing process. Consequently, the TPN-loaded PLGA-PEG-PLGA thermogel is a good candidate of wound dressing for full-thickness excision wound healing.
Bacterial infection is a very troublesome issue in wound treatment, which stimulates exudate formation and severely delays the healing process. Herein, a thermogelling dressing system composed of two triblock copolymers of poly(D,L-lactic acid-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(D,L-lactic acid-co-glycolic acid) (PLGA-PEG-PLGA) with different block lengths was developed to deliver teicoplanin (TPN), a glycopeptide antibiotic, for cutaneous wound repair. The TPN-loaded thermogel was a free-flowing sol at room temperature and formed a semi-solid gel at physiological temperature. In vitro studies demonstrated that the TPN-loaded thermogel system exhibited desired tissue adhesiveness and realized the sustained release of TPN in a fast-followed-slow manner for over three weeks. Furthermore, a full-thickness excision wound model in Sprague-Dawley (SD) rats was constructed to assess the efficacy of TPN-loaded thermogel formulation. Gross and histopathologic observations implied that treatment with the thermogel formulation reduced inflammation response, promoted disposition of collagen, enhanced angiogenesis, and accelerated wound closure and maturity of SD rats. The combination of the bioactivity of TPN and the acidic nature of the thermogel matrix was responsible for such an enhanced wound healing process. Consequently, the TPN-loaded PLGA-PEG-PLGA thermogel is a good candidate of wound dressing for full-thickness excision wound healing.
2019, 37(6): 560-569
doi: 10.1007/s10118-019-2231-2
Abstract:
Electrospun nanofibrous mats represent a new generation of medical textiles with promising applications in heart valve tissue reconstruction. It is important for biomaterials to mimic the biological and mechanical microenvironment of native extracellular matrix (ECM). However, the major challenges are still remaining for current biomedical materials, including appropriate mechanical properties, biocompatibility, and hemocompatibility. In the present work, the novel composite nanofibrous mats of poly(p-dioxanone) (PDO) and poly(ester-urethane)ureas (PEUU) are fabricated by electrospinning system. The optimal combination ratio of PDO to PEUU may balance the mechanical properties and cellular compatibility to match the newly formed tissue. In PDO/PEUU composite nanofibrous mats, PEUU can provide the biomimetic elastomeric behavior, and PDO could endow the excellent biocompatibility. In comparison to nanofibrous mat of neat PDO, the composite showed significantly improved mechanical properties, with 5-fold higher initial elongation at break. Furthermore, human umbilical vein endothelial cells (HUVECs) were cultured on the composite to evaluate its ability to rapidly endothelialize as heart valve tissue engineering. The results revealed that PDO/PEUU composite nanofibrous mats could promote cell adhesion and proliferation, especially for the ratio of 60/40. Overall, PDO/PEUU composite nanofibrous mats (60/40) show the excellent mechanical properties, appropriate biocompatibility and hemocompatibility which meet the necessary norm for tissue engineering and may be suitable for potential heart valve tissue reconstruction.
Electrospun nanofibrous mats represent a new generation of medical textiles with promising applications in heart valve tissue reconstruction. It is important for biomaterials to mimic the biological and mechanical microenvironment of native extracellular matrix (ECM). However, the major challenges are still remaining for current biomedical materials, including appropriate mechanical properties, biocompatibility, and hemocompatibility. In the present work, the novel composite nanofibrous mats of poly(p-dioxanone) (PDO) and poly(ester-urethane)ureas (PEUU) are fabricated by electrospinning system. The optimal combination ratio of PDO to PEUU may balance the mechanical properties and cellular compatibility to match the newly formed tissue. In PDO/PEUU composite nanofibrous mats, PEUU can provide the biomimetic elastomeric behavior, and PDO could endow the excellent biocompatibility. In comparison to nanofibrous mat of neat PDO, the composite showed significantly improved mechanical properties, with 5-fold higher initial elongation at break. Furthermore, human umbilical vein endothelial cells (HUVECs) were cultured on the composite to evaluate its ability to rapidly endothelialize as heart valve tissue engineering. The results revealed that PDO/PEUU composite nanofibrous mats could promote cell adhesion and proliferation, especially for the ratio of 60/40. Overall, PDO/PEUU composite nanofibrous mats (60/40) show the excellent mechanical properties, appropriate biocompatibility and hemocompatibility which meet the necessary norm for tissue engineering and may be suitable for potential heart valve tissue reconstruction.
2019, 37(6): 570-577
doi: 10.1007/s10118-019-2209-0
Abstract:
Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl3 followed by the addition of two equivalents of LiCH2SiMe3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl) complexes (Cp′CH2-Py)Ln(CH2SiMe3)2(THF)n (Py = C5H4N, Cp′ = C5H4 (Cp), Ln = Sc, n = 0 (1); Cp′ = C9H6 (Ind), Ln = Sc, n = 0 (2); Cp′ = 3-Me3Si-C9H5 (3-Me3Si-Ind), Ln = Sc, n = 0 (3a), Ln = Lu (3b), Y (3c), n = 1; Cp′ = 2,7-(tBu)2C13H8 (2,7-(tBu)2-Flu), Ln = Sc (4a), n = 0, Ln = Lu (4b), Y (4c), n = 1) in moderate to good yields, which were characterized by NMR spectroscopy and single-crystal X-ray diffraction (for complex 3a). In the presence of [Ph3C][B(C6F5)4] and AliBu3, these complexes displayed different performances towards styrene polymerization. Rare-earth metal bis(alkyl) precursors bearing Cp, Ind, and 3-Me3Si-Ind segments exhibited very low catalytic activity to afford syndiotactic polystyrene. All electron-donating tBu substituted complexes 4a, 4b, and 4c showed very high activity and perfect syndiotactivity (rrrr > 99%), producing high molecular weight polystyrene (up to 54.1 × 104) with relatively narrow molecular distribution (PDI = 1.28−2.49).
Salt metathesis reactions between pyridyl-methylene-cyclopentadienyl lithium salt and LnCl3 followed by the addition of two equivalents of LiCH2SiMe3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl) complexes (Cp′CH2-Py)Ln(CH2SiMe3)2(THF)n (Py = C5H4N, Cp′ = C5H4 (Cp), Ln = Sc, n = 0 (1); Cp′ = C9H6 (Ind), Ln = Sc, n = 0 (2); Cp′ = 3-Me3Si-C9H5 (3-Me3Si-Ind), Ln = Sc, n = 0 (3a), Ln = Lu (3b), Y (3c), n = 1; Cp′ = 2,7-(tBu)2C13H8 (2,7-(tBu)2-Flu), Ln = Sc (4a), n = 0, Ln = Lu (4b), Y (4c), n = 1) in moderate to good yields, which were characterized by NMR spectroscopy and single-crystal X-ray diffraction (for complex 3a). In the presence of [Ph3C][B(C6F5)4] and AliBu3, these complexes displayed different performances towards styrene polymerization. Rare-earth metal bis(alkyl) precursors bearing Cp, Ind, and 3-Me3Si-Ind segments exhibited very low catalytic activity to afford syndiotactic polystyrene. All electron-donating tBu substituted complexes 4a, 4b, and 4c showed very high activity and perfect syndiotactivity (rrrr > 99%), producing high molecular weight polystyrene (up to 54.1 × 104) with relatively narrow molecular distribution (PDI = 1.28−2.49).
2019, 37(6): 578-590
doi: 10.1007/s10118-019-2224-1
Abstract:
Four C1-symmetric ansa-metallocene complexes, C2H4(Ind)(2,7-tBu2-Flu)ZrCl2 (4), C2H4(3-Bn-Ind)(2,7-tBu2-Flu)ZrCl2 (5), C2H4(3-Bn-Ind)(3,6-tBu2-Flu)ZrCl2 (6), and C2H4(3-Bn-Ind)(2,7-tBu2-Flu)HfCl2 (7), were synthesized and characterized. The structures of complexes 4, 5, and 7 were further determined via X-ray diffraction studies. Upon activation with modified methylaluminoxane (MMAO) or AliBu3/[Ph3C][B(C6F5)4] (TIBA/TrB), most of these complexes showed high efficiency in catalyzing propylene oligomerization/polymerization to afford products dominantly with allyl terminals via selective β-methyl transfer (β-Me transfer). The introduction of 3-benzyl group on the indenyl ring of the complexes was found to be crucial in enabling highly selective β-Me transfer during the polymerization process, leading to selectivities up to 89% obtained by zirconocene complexes 5 and 6, and up to 91% obtained by hafnocene complex 7. Detailed chain-end analysis by 1H-NMR, 13C-NMR, and MALDI-TOF mass spectroscopy revealed that the allyl chain-ends of the polymeric products resulted from a selective β-Me transfer process after two successively primary insertions of the monomer. Further studies concerning the dependence of chain release selectivity as well as the molecular weight of products on monomer concentration suggested that both β-Me transfer (major) and β-hydrogen transfer (β-H transfer) (minor) mediated by 5/MMAO and 6/MMAO systems may mainly operate in a bimolecular pathway.
Four C1-symmetric ansa-metallocene complexes, C2H4(Ind)(2,7-tBu2-Flu)ZrCl2 (4), C2H4(3-Bn-Ind)(2,7-tBu2-Flu)ZrCl2 (5), C2H4(3-Bn-Ind)(3,6-tBu2-Flu)ZrCl2 (6), and C2H4(3-Bn-Ind)(2,7-tBu2-Flu)HfCl2 (7), were synthesized and characterized. The structures of complexes 4, 5, and 7 were further determined via X-ray diffraction studies. Upon activation with modified methylaluminoxane (MMAO) or AliBu3/[Ph3C][B(C6F5)4] (TIBA/TrB), most of these complexes showed high efficiency in catalyzing propylene oligomerization/polymerization to afford products dominantly with allyl terminals via selective β-methyl transfer (β-Me transfer). The introduction of 3-benzyl group on the indenyl ring of the complexes was found to be crucial in enabling highly selective β-Me transfer during the polymerization process, leading to selectivities up to 89% obtained by zirconocene complexes 5 and 6, and up to 91% obtained by hafnocene complex 7. Detailed chain-end analysis by 1H-NMR, 13C-NMR, and MALDI-TOF mass spectroscopy revealed that the allyl chain-ends of the polymeric products resulted from a selective β-Me transfer process after two successively primary insertions of the monomer. Further studies concerning the dependence of chain release selectivity as well as the molecular weight of products on monomer concentration suggested that both β-Me transfer (major) and β-hydrogen transfer (β-H transfer) (minor) mediated by 5/MMAO and 6/MMAO systems may mainly operate in a bimolecular pathway.
2019, 37(6): 591-597
doi: 10.1007/s10118-019-2236-x
Abstract:
Cu(0)-mediated reversible deactivation radical polymerization (Cu(0)-mediated RDRP) has been demonstrated as an excellent technique to control the polymerization of multiple vinyl monomers (e.g., acrylates, methacrylates, and styrene). However, the complexity of the reaction mechanism and multi-component system nature make it challenging to choose the appropriate conditions and consider the factors of achieving controllable polymerization when switching from one monomer to others with different reactivities. Herein, by polymerizing two examplary monomers: methyl methacrylate (MMA) and styrene via Cu(0)-mediated RDRP under different conditions, we have found that the reaction parameters (e.g., initiator, ligand, solvent, and deactivator) play a crucial role in regulating two equilibriums: (i) mutual conversion of different copper species which determines the relative concentration of Cu(I) and Cu(II), and (ii) polymerization equilibrium which is the combination of activation/deactivation, propagation and termination processes. We have demonstrated that by taking both the mutual conversion of different copper species and the polymerization equilibrium into account, the optimal reaction conditions could be selected, and the well-controlled Cu(0)-mediated RDRPs of methyl methacrylate and styrene were achieved with narrow molecular weight distributions and predicted molecular weight.
Cu(0)-mediated reversible deactivation radical polymerization (Cu(0)-mediated RDRP) has been demonstrated as an excellent technique to control the polymerization of multiple vinyl monomers (e.g., acrylates, methacrylates, and styrene). However, the complexity of the reaction mechanism and multi-component system nature make it challenging to choose the appropriate conditions and consider the factors of achieving controllable polymerization when switching from one monomer to others with different reactivities. Herein, by polymerizing two examplary monomers: methyl methacrylate (MMA) and styrene via Cu(0)-mediated RDRP under different conditions, we have found that the reaction parameters (e.g., initiator, ligand, solvent, and deactivator) play a crucial role in regulating two equilibriums: (i) mutual conversion of different copper species which determines the relative concentration of Cu(I) and Cu(II), and (ii) polymerization equilibrium which is the combination of activation/deactivation, propagation and termination processes. We have demonstrated that by taking both the mutual conversion of different copper species and the polymerization equilibrium into account, the optimal reaction conditions could be selected, and the well-controlled Cu(0)-mediated RDRPs of methyl methacrylate and styrene were achieved with narrow molecular weight distributions and predicted molecular weight.
2019, 37(6): 598-603
doi: 10.1007/s10118-019-2228-x
Abstract:
The anionic polymerization of methyl methacrylate (MMA) was carried out using phosphazene base t-BuP4 and ethyl acetate (EA) as the catalyst and the initiator, respectively. Gas chromatography (GC), size exclusion chromatography (SEC) measurements, and nuclear magnetic resonance (NMR) analyses were used to reveal the polymerization mechanism and to confirm the polymer structure. The results confirmed the proposed polymerization mechanism and the polymer structure, while the initiator efficiency was low. Meanwhile, the initiation by methoxy anion coming from hydrolysis of the ester bond in MMA was also observed. As a result, there is a marked deviation between the theoretical molecular weight and the measured molecular weight, and it is essential to carry out the polymerization at excessive dosage of t-BuP4 for preparing polymers with narrow molecular weight distribution.
The anionic polymerization of methyl methacrylate (MMA) was carried out using phosphazene base t-BuP4 and ethyl acetate (EA) as the catalyst and the initiator, respectively. Gas chromatography (GC), size exclusion chromatography (SEC) measurements, and nuclear magnetic resonance (NMR) analyses were used to reveal the polymerization mechanism and to confirm the polymer structure. The results confirmed the proposed polymerization mechanism and the polymer structure, while the initiator efficiency was low. Meanwhile, the initiation by methoxy anion coming from hydrolysis of the ester bond in MMA was also observed. As a result, there is a marked deviation between the theoretical molecular weight and the measured molecular weight, and it is essential to carry out the polymerization at excessive dosage of t-BuP4 for preparing polymers with narrow molecular weight distribution.
2019, 37(6): 604-608
doi: 10.1007/s10118-019-2234-z
Abstract:
Buckyballs (C60) are linked to one end and two ends of linear poly(ethylene oxide) (PEO) chains through highly efficient click chemistry to obtain giant amphiphilic molecules C60-PEO and C60-PEO-C60, respectively. C60-PEO and C60-PEO-C60 molecules are spread on water surface and then transferred to solid substrates with Langmuir-Blodgett (LB) film deposition approach. C60-PEO and C60-PEO-C60 exhibit fractal growth behavior on the solid substrate under certain conditions owing to the crystallization ability of PEO segment. PEO chain length and the end capped mode both affect the fractal growth pattern.
Buckyballs (C60) are linked to one end and two ends of linear poly(ethylene oxide) (PEO) chains through highly efficient click chemistry to obtain giant amphiphilic molecules C60-PEO and C60-PEO-C60, respectively. C60-PEO and C60-PEO-C60 molecules are spread on water surface and then transferred to solid substrates with Langmuir-Blodgett (LB) film deposition approach. C60-PEO and C60-PEO-C60 exhibit fractal growth behavior on the solid substrate under certain conditions owing to the crystallization ability of PEO segment. PEO chain length and the end capped mode both affect the fractal growth pattern.
2019, 37(6): 609-616
doi: 10.1007/s10118-019-2235-y
Abstract:
Superhydrophobic poly(vinylidene fluoride) (PVDF) membrane incorporated with nanoparticles was applied in membrane distillation to recover water from phenolic rich solution containing surfactant. The membranes coated on woven support were fabricated using phase inversion with dual bath coagulation and post-modified using silane. The membranes incorporated with TiO2, SiO2, or a mixture of TiO2-SiO2 nanoparticles achieved the water contact angle higher than 160°. The addition of TiO2-SiO2 mixture into PVDF matrix further enhanced the hierarchical roughness of membrane. Hence, PVDF/TiO2-SiO2 membrane achieved the highest permeation flux and rejected 99.9% of gallic acid in the feed (100 g/L). PVDF/TiO2-SiO2 membrane also maintained a relative flux (J/J0) higher than 0.9 after 8 h of operation. Even with the presence of surfactant in phenolic rich solution, PVDF/TiO2-SiO2 membrane was able to exhibit relative flux above 0.8. The significant changes on the hydrophobicity and chemical properties of PVDF/TiO2-SiO2 membrane due to fouling were not observed after 50 h of static adsorption test.
Superhydrophobic poly(vinylidene fluoride) (PVDF) membrane incorporated with nanoparticles was applied in membrane distillation to recover water from phenolic rich solution containing surfactant. The membranes coated on woven support were fabricated using phase inversion with dual bath coagulation and post-modified using silane. The membranes incorporated with TiO2, SiO2, or a mixture of TiO2-SiO2 nanoparticles achieved the water contact angle higher than 160°. The addition of TiO2-SiO2 mixture into PVDF matrix further enhanced the hierarchical roughness of membrane. Hence, PVDF/TiO2-SiO2 membrane achieved the highest permeation flux and rejected 99.9% of gallic acid in the feed (100 g/L). PVDF/TiO2-SiO2 membrane also maintained a relative flux (J/J0) higher than 0.9 after 8 h of operation. Even with the presence of surfactant in phenolic rich solution, PVDF/TiO2-SiO2 membrane was able to exhibit relative flux above 0.8. The significant changes on the hydrophobicity and chemical properties of PVDF/TiO2-SiO2 membrane due to fouling were not observed after 50 h of static adsorption test.
2019, 37(6): 617-626
doi: 10.1007/s10118-019-2219-y
Abstract:
The growing demand for non-toxic solvents for membrane preparation has motivated the studies for green and sustainable alternatives of solvents. The effect of droplet isothermal growth within the liquid-liquid phase separation region on isothermal spherulitic growth rate of isotactic polypropylene (iPP) was investigated. The results showed that the droplets grew up at a rate of 0.0172 μm·s−1. The larger droplets slowed down the isothermal spherulitic growth rate of iPP. Higher mass ratio of carnauba wax (Cwax)/soybean oil (SO) resulted in faster droplet growth due to weak interaction with polymers. The isothermal crystallization behaviors of iPP in environment-friendly binary diluents consisting of Cwax and SO mixture were further investigated experimentally using polarized optical microscopy. It was demonstrated that the isothermal spherulitic growth rate of iPP in diluents decreased nonlinearly with the increasing crystallization temperature. Compared with virgin iPP, isothermal spherulitic growth rate of iPP in SO diluent was significantly slowed down. The spherulitic growth was further retarded after the addition of Cwax in mixed diluents, resulting in a lower crystallization rate than that in SO. Moreover, the crystal form of iPP membranes was found to be α type through the characterization of small angle X-ray scattering and wide angle X-ray diffraction.
The growing demand for non-toxic solvents for membrane preparation has motivated the studies for green and sustainable alternatives of solvents. The effect of droplet isothermal growth within the liquid-liquid phase separation region on isothermal spherulitic growth rate of isotactic polypropylene (iPP) was investigated. The results showed that the droplets grew up at a rate of 0.0172 μm·s−1. The larger droplets slowed down the isothermal spherulitic growth rate of iPP. Higher mass ratio of carnauba wax (Cwax)/soybean oil (SO) resulted in faster droplet growth due to weak interaction with polymers. The isothermal crystallization behaviors of iPP in environment-friendly binary diluents consisting of Cwax and SO mixture were further investigated experimentally using polarized optical microscopy. It was demonstrated that the isothermal spherulitic growth rate of iPP in diluents decreased nonlinearly with the increasing crystallization temperature. Compared with virgin iPP, isothermal spherulitic growth rate of iPP in SO diluent was significantly slowed down. The spherulitic growth was further retarded after the addition of Cwax in mixed diluents, resulting in a lower crystallization rate than that in SO. Moreover, the crystal form of iPP membranes was found to be α type through the characterization of small angle X-ray scattering and wide angle X-ray diffraction.
2019, 37(6): 627-632
doi: 10.1007/s10118-019-2222-3
Abstract:
We performed kinetic Monte Carlo simulations of a lattice polymer model holding intramolecular and intermolecular activation barriers for polymer diffusion, on the basis of the previous dynamic Monte Carlo simulations of polymer crystallization. We explored the effective parameter sets for two barriers to freeze the amorphous polymers at low temperatures. The subsequent heating process of the frozen amorphous polymers exhibits clear cold crystallization behaviors. We made preliminary investigation on the crystallinity and the morphology of polymer crystallites yielded during the cold crystallization, which appear in consistence with our common experimental observations. Our present work paves the way for molecular simulations of hot and cold polymer crystallization in the whole temperature range between the glass transition temperature and the melting temperature.
We performed kinetic Monte Carlo simulations of a lattice polymer model holding intramolecular and intermolecular activation barriers for polymer diffusion, on the basis of the previous dynamic Monte Carlo simulations of polymer crystallization. We explored the effective parameter sets for two barriers to freeze the amorphous polymers at low temperatures. The subsequent heating process of the frozen amorphous polymers exhibits clear cold crystallization behaviors. We made preliminary investigation on the crystallinity and the morphology of polymer crystallites yielded during the cold crystallization, which appear in consistence with our common experimental observations. Our present work paves the way for molecular simulations of hot and cold polymer crystallization in the whole temperature range between the glass transition temperature and the melting temperature.
