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2009 Volume 27 Issue 1
2009, 27(1): 1-9
Abstract:
Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft wet materials, suitable for making artificial organs for medical treatments.However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels.
Living tissues work with fantastic functions in soft and wet gel-like state. Thus, hydrogels have attracted much attention as excellent soft wet materials, suitable for making artificial organs for medical treatments.However, conventional hydrogels are mechanically too weak for practical uses. We have created double network (DN) hydrogels with extremely high mechanical strength in order to overcome this problem. DN gels are interpenetrating network (IPN) hydrogels consisting of rigid polyelectrolyte and soft neutral polymer. Their excellent mechanical properties cannot be explained by the standard fracture theories. In this paper, we discuss about the toughening mechanism of DN gels in accordance with their characteristic behavior, such as large hysteresis and necking phenomenon. We also describe the results on tissue engineering application of DN gels.
2009, 27(1): 11-22
Abstract:
Polymeric systems have played an important role as structure-directing agents and in the control of nucleation and growth of crystals. This article reviews the work of our research group in the field of the polymer-assisted crystallization of inorganic materials, mainly focused on the formation of highly ordered, porous molybdenum oxide nanostructures. Different experimental parameters including the influence of poly(ethylene oxide)-containing polymers on the morphology and structure of the products obtained from peroxomolybdate solutions are examined. Our electrochemical investigations on molybdate species are also briefly described. Finally, the importance of the precursor species in the formation of the final product is discussed.
Polymeric systems have played an important role as structure-directing agents and in the control of nucleation and growth of crystals. This article reviews the work of our research group in the field of the polymer-assisted crystallization of inorganic materials, mainly focused on the formation of highly ordered, porous molybdenum oxide nanostructures. Different experimental parameters including the influence of poly(ethylene oxide)-containing polymers on the morphology and structure of the products obtained from peroxomolybdate solutions are examined. Our electrochemical investigations on molybdate species are also briefly described. Finally, the importance of the precursor species in the formation of the final product is discussed.
2009, 27(1): 23-36
Abstract:
The roles of reaction inhomogeneity in phase separation of polymer mixtures were described and summarized via two examples: photocross-link of polymer mixtures in the bulk state and photopolymerization of monomer in the liquid state. The reaction kinetics, the reaction-induced elastic strain and the phase separation kinetics were monitored respectively by UV-Vis spectroscopy, Mach-Zehnder interferometry and laser-scanning confocal microscopy. It was found that phase separation in the bulk state was strongly influenced by the elastic strain associated with the intrinsic inhomogeneity of the reaction, whereas the autocatalytic behavior of the polymerization plays an important role in the resulting morphology in the liquid state. These experimental results are discussed in conjunction with the morphology control of polymer mixtures by using chemical reactions.
The roles of reaction inhomogeneity in phase separation of polymer mixtures were described and summarized via two examples: photocross-link of polymer mixtures in the bulk state and photopolymerization of monomer in the liquid state. The reaction kinetics, the reaction-induced elastic strain and the phase separation kinetics were monitored respectively by UV-Vis spectroscopy, Mach-Zehnder interferometry and laser-scanning confocal microscopy. It was found that phase separation in the bulk state was strongly influenced by the elastic strain associated with the intrinsic inhomogeneity of the reaction, whereas the autocatalytic behavior of the polymerization plays an important role in the resulting morphology in the liquid state. These experimental results are discussed in conjunction with the morphology control of polymer mixtures by using chemical reactions.
2009, 27(1): 37-47
Abstract:
Nano-mechanical mapping by atomic force microscopy has been developed as an useful application to measure mechanical properties of soft materials at nanometer scale. To date, the Hertzian theory was used for analyzing force-distance curves as the simplest model among several contact mechanics between elastic bodies. However, the preexisting methods based on this theory do not consider the adhesive interaction in principle, which cannot be neglected in the ambient condition. A new analytical method was introduced to estimate the elasticity and the adhesive energy simultaneously by means of the JKR theory, describing adhesive contact between elastic materials. Poly(dimethylsiloxane) (PDMS) and isobutylene-co-isoprene rubber (IIR) were analyzed to verify the applicable limit of the JKR analysis. For elastic samples such as PDMS, the force-deformation plots obtained experimentally were consistent with JKR theoretical curves. Meanwhile, for viscoelastic samples, especially for IIR, the experimental plots revealed large deviations from JKR curves depending on scanning velocity and maximum loading force. Some nano-rheological arguments were employed based on the difference between these specimens.
Nano-mechanical mapping by atomic force microscopy has been developed as an useful application to measure mechanical properties of soft materials at nanometer scale. To date, the Hertzian theory was used for analyzing force-distance curves as the simplest model among several contact mechanics between elastic bodies. However, the preexisting methods based on this theory do not consider the adhesive interaction in principle, which cannot be neglected in the ambient condition. A new analytical method was introduced to estimate the elasticity and the adhesive energy simultaneously by means of the JKR theory, describing adhesive contact between elastic materials. Poly(dimethylsiloxane) (PDMS) and isobutylene-co-isoprene rubber (IIR) were analyzed to verify the applicable limit of the JKR analysis. For elastic samples such as PDMS, the force-deformation plots obtained experimentally were consistent with JKR theoretical curves. Meanwhile, for viscoelastic samples, especially for IIR, the experimental plots revealed large deviations from JKR curves depending on scanning velocity and maximum loading force. Some nano-rheological arguments were employed based on the difference between these specimens.
2009, 27(1): 49-57
Abstract:
Films obtained via drying a polymeric latex dispersion are normally colloidal crystalline where latex particles are packed into a face centered cubic (fcc) structure. Different from conventional atomic crystallites or hard sphere colloidal crystallites, the crystalline structure of these films is normally deformable due to the low glass transition temperature of the latex particles. Upon tensile deformation, depending on the drawing direction with respect to the normal of specific crystallographic plane, one observes different crystalline structural changes. Three typical situations where crystallographic c-axis, body diagonal or face diagonal of the fcc structure of the colloidal crystallites being parallel to the stretching direction were investigated. Tilting angle and d-spacing of several crystallographic planes as a function of draw ratio at each situation were derived. Experimental evidences for such relationships were also given by considering in-situ synchrotron small angle X-ray scattering data of a typical latex film during stretching. It turns out that the experimental results are fully in accordance with the mathematical calculations.
Films obtained via drying a polymeric latex dispersion are normally colloidal crystalline where latex particles are packed into a face centered cubic (fcc) structure. Different from conventional atomic crystallites or hard sphere colloidal crystallites, the crystalline structure of these films is normally deformable due to the low glass transition temperature of the latex particles. Upon tensile deformation, depending on the drawing direction with respect to the normal of specific crystallographic plane, one observes different crystalline structural changes. Three typical situations where crystallographic c-axis, body diagonal or face diagonal of the fcc structure of the colloidal crystallites being parallel to the stretching direction were investigated. Tilting angle and d-spacing of several crystallographic planes as a function of draw ratio at each situation were derived. Experimental evidences for such relationships were also given by considering in-situ synchrotron small angle X-ray scattering data of a typical latex film during stretching. It turns out that the experimental results are fully in accordance with the mathematical calculations.
2009, 27(1): 71-76
Abstract:
2H-NMR spectroscopy of the probe molecule, deuterated benzene, was applied to characterize organo-clay dispersion and confinement effect on the local motion of benzene in rubber/clay nanocomposite-gels. The observed 2H line shapes of benzene in intercalated and exfoliated nanocomposites were obviously different, which can be used to estimate clay-dispersion quality. 2H-NMR line shapes also reflect the different influence of intercalated or exfoliated layered-silicates on local motions of benzene, implying that probe molecules exhibit different local motions depending on different confined geometry in these nanocomposites. Viscosity measurements further confirmed these NMR results.
2H-NMR spectroscopy of the probe molecule, deuterated benzene, was applied to characterize organo-clay dispersion and confinement effect on the local motion of benzene in rubber/clay nanocomposite-gels. The observed 2H line shapes of benzene in intercalated and exfoliated nanocomposites were obviously different, which can be used to estimate clay-dispersion quality. 2H-NMR line shapes also reflect the different influence of intercalated or exfoliated layered-silicates on local motions of benzene, implying that probe molecules exhibit different local motions depending on different confined geometry in these nanocomposites. Viscosity measurements further confirmed these NMR results.
2009, 27(1): 77-83
Abstract:
Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics, diagnostics, drug delivery, UV-absorbers etc. Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques. Applications of techniques like mass spectroscopy, transmission electron microscopy as well as ultracentrifugation to problems arising from nanotechnology in the chemical industry will be described
Apart from long-known and applied nanostructures like carbon black for tyres or pigments for coatings nanotechnology has created highly sophisticated structures used for nano/molecular electronics, diagnostics, drug delivery, UV-absorbers etc. Often the main question to be solved analytically is the local determination of tiny amounts of chemicals resulting in an ever increasing need for highly sensitive as well as locally resolved techniques. Applications of techniques like mass spectroscopy, transmission electron microscopy as well as ultracentrifugation to problems arising from nanotechnology in the chemical industry will be described
2009, 27(1): 85-92
Abstract:
In this study, the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography. After annealing treatment, either at elevated temperature or during slow solvent evaporation, nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer. Such a tailored morphology accounts for the considerable increase of the power conversion efficiency in corresponding solar cell devices.
In this study, the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography. After annealing treatment, either at elevated temperature or during slow solvent evaporation, nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer. Such a tailored morphology accounts for the considerable increase of the power conversion efficiency in corresponding solar cell devices.
2009, 27(1): 93-100
Abstract:
Polymer-supported ruthenium complexes #9413;-Phen-Ru-①, #9413;-Phen-Ru-②, #9413;-Phen-Ru-③, #9413;-Phen-Ru-④, #9413;-Phen-Ru-⑤, #9413;-Phen-Ru-⑥ and #9413;-Phen-Ru-⑦ were prepared using aminomethyl polystyrenes of different morphological structures as supports. A variety of alcohols were oxidized efficiently into the corresponding ketones, carboxylic acids or aldehydes with iodosylbenzene (PhIO) catalyzed by aminomethyl polystyrene-supported ruthenium complexes under mild reaction conditions in acetonitrile. The influences of morphological structure of the polymer supporters on the catalytic properties of these metal complexes were investigated in detail.
Polymer-supported ruthenium complexes #9413;-Phen-Ru-①, #9413;-Phen-Ru-②, #9413;-Phen-Ru-③, #9413;-Phen-Ru-④, #9413;-Phen-Ru-⑤, #9413;-Phen-Ru-⑥ and #9413;-Phen-Ru-⑦ were prepared using aminomethyl polystyrenes of different morphological structures as supports. A variety of alcohols were oxidized efficiently into the corresponding ketones, carboxylic acids or aldehydes with iodosylbenzene (PhIO) catalyzed by aminomethyl polystyrene-supported ruthenium complexes under mild reaction conditions in acetonitrile. The influences of morphological structure of the polymer supporters on the catalytic properties of these metal complexes were investigated in detail.
2009, 27(1): 101-108
Abstract:
Poly(styrene-co-glycidyl methacrylate) latex microspheres with uniform size and high-density epoxy groups on the surface were prepared by soap-free emulsion polymerization with batch wise operation mode in the presence of 2,2-azobis(2-methylpropionamidine) dihydrochloride as an initiator. The kinetics of soap-free emulsion polymerization and the effects of polymerization factors were examined. In addition, the optimum polymerization conditions of poly(styrene-co-glycidyl methacrylate) latex microspheres for immobilization of biomolecules were obtained.
Poly(styrene-co-glycidyl methacrylate) latex microspheres with uniform size and high-density epoxy groups on the surface were prepared by soap-free emulsion polymerization with batch wise operation mode in the presence of 2,2-azobis(2-methylpropionamidine) dihydrochloride as an initiator. The kinetics of soap-free emulsion polymerization and the effects of polymerization factors were examined. In addition, the optimum polymerization conditions of poly(styrene-co-glycidyl methacrylate) latex microspheres for immobilization of biomolecules were obtained.
2009, 27(1): 109-114
Abstract:
The behavior of three-dimensional bond fluctuation model chains tethered on an adsorbing flat surface was simulated by the Monte Carlo method. The dependence of the number of surface contacts M on the interaction strength e and the chain length N was investigated by a finite-size scaling law M = N[a0 + a1N1/vk + O((N 1/vk)2)] for e near the critical adsorption point ec, i.e., k ≡(e-ec)/ec closes to 0. The critical adsorption point was estimated to be ec = 0.93, and the exponents = 0.49 and 1/v= 0.57.
The behavior of three-dimensional bond fluctuation model chains tethered on an adsorbing flat surface was simulated by the Monte Carlo method. The dependence of the number of surface contacts M on the interaction strength e and the chain length N was investigated by a finite-size scaling law M = N[a0 + a1N1/vk + O((N 1/vk)2)] for e near the critical adsorption point ec, i.e., k ≡(e-ec)/ec closes to 0. The critical adsorption point was estimated to be ec = 0.93, and the exponents = 0.49 and 1/v= 0.57.
2009, 27(1): 115-120
Abstract:
Electrospraying/electrospinning of poly(γ-stearyl-L-glutamate) (PSLG) was investigated on a series solutions with different concentrations in chloroform. Field emission scanning electron microscopy (FESEM) and attenuated total reflectance Fourier transform infrared spectroscopy (FT-IR/ATR) were used to characterize the morphology and structure of the electrosprayed/electrospun polypeptide mats. It was found that electrospraying of PSLG with concentrations lower than 16 wt% afforded beads, while microfibers could be electrospun at the concentration of 22 wt%. The hydrophobicity of the electrosprayed/electrospun PSLG mats was investigated with static water contact angle (WCA) and tilt angle measurements. It was demonstrated that the superhydrophobic surfaces of PSLG with WCAs and tilt angles in the ranges of 150°-170° and 16.5°-4.2°, respectively, were obtained through electrospraying/electrospinning process.
Electrospraying/electrospinning of poly(γ-stearyl-L-glutamate) (PSLG) was investigated on a series solutions with different concentrations in chloroform. Field emission scanning electron microscopy (FESEM) and attenuated total reflectance Fourier transform infrared spectroscopy (FT-IR/ATR) were used to characterize the morphology and structure of the electrosprayed/electrospun polypeptide mats. It was found that electrospraying of PSLG with concentrations lower than 16 wt% afforded beads, while microfibers could be electrospun at the concentration of 22 wt%. The hydrophobicity of the electrosprayed/electrospun PSLG mats was investigated with static water contact angle (WCA) and tilt angle measurements. It was demonstrated that the superhydrophobic surfaces of PSLG with WCAs and tilt angles in the ranges of 150°-170° and 16.5°-4.2°, respectively, were obtained through electrospraying/electrospinning process.
2009, 27(1): 121-130
Abstract:
Some copolymers of 2,4-dichlorophenyl acrylate (2,4-DCPA) with styrene (St) of different feed compositions were prepared by free radical polymerization technique using 2,2 -azobisisobutyronitrile (AIBN) as an initiator, and the copolymers were characterized by IR spectroscopy. The copolymer composition obtained by UV-spectra led to determination of reactivity ratio by employing Fineman-Ross (F-R) and Kelen-Tudos (K-T) methods. Average molecular weight, as well as intrinsic viscosity, was obtained by vapor pressure osmometry (VPO) and Ubbleholde viscometer. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of copolymers were carried out under nitrogen atmosphere. Antimicrobial effects of the homo and copolymers were also investigated against various microorganisms such as bacteria, fungi and yeasts.
Some copolymers of 2,4-dichlorophenyl acrylate (2,4-DCPA) with styrene (St) of different feed compositions were prepared by free radical polymerization technique using 2,2 -azobisisobutyronitrile (AIBN) as an initiator, and the copolymers were characterized by IR spectroscopy. The copolymer composition obtained by UV-spectra led to determination of reactivity ratio by employing Fineman-Ross (F-R) and Kelen-Tudos (K-T) methods. Average molecular weight, as well as intrinsic viscosity, was obtained by vapor pressure osmometry (VPO) and Ubbleholde viscometer. Thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of copolymers were carried out under nitrogen atmosphere. Antimicrobial effects of the homo and copolymers were also investigated against various microorganisms such as bacteria, fungi and yeasts.
2009, 27(1): 131-136
Abstract:
Two poly(Schiff base)s (PDBT and PDPE) were synthesized by polycondensation of 1,10-phenanthroline-5,6-dione (PD) with 2,2′-diamino-4,4′-bithiazole (DABT) and 4,4′-diaminodiphenyl ether (DAPE), respectively. The structures of the polymers were determined by FTIR and element analysis. The metal (Fe2+, Ni2+) complexes were prepared from the polymers with FeSO4 or NiSO4, and the metal contents of the complexes were measured by complexometric titration. The magnetic behaviors of the complexes were examined as a function of magnetic field strength at 4 K and as a function of temperature (4-300 K) at a magnetic field strength of 2.4 ×106 A/m. The results show that the relative saturation magnetization of the PDBT complexes is higher than that of the corresponding PDPE complexes, and PDBT-Ni2+ and PDPE-Ni2+ are soft ferromagnets, while PDBT-Fe2+ and PDPE-Fe2+ exhibit the features of antiferromagnet.
Two poly(Schiff base)s (PDBT and PDPE) were synthesized by polycondensation of 1,10-phenanthroline-5,6-dione (PD) with 2,2′-diamino-4,4′-bithiazole (DABT) and 4,4′-diaminodiphenyl ether (DAPE), respectively. The structures of the polymers were determined by FTIR and element analysis. The metal (Fe2+, Ni2+) complexes were prepared from the polymers with FeSO4 or NiSO4, and the metal contents of the complexes were measured by complexometric titration. The magnetic behaviors of the complexes were examined as a function of magnetic field strength at 4 K and as a function of temperature (4-300 K) at a magnetic field strength of 2.4 ×106 A/m. The results show that the relative saturation magnetization of the PDBT complexes is higher than that of the corresponding PDPE complexes, and PDBT-Ni2+ and PDPE-Ni2+ are soft ferromagnets, while PDBT-Fe2+ and PDPE-Fe2+ exhibit the features of antiferromagnet.
2009, 27(1): 137-143
Abstract:
A series of polydimethylsiloxane (PDMS) with varied molecular weights (Mw = 3 106, 1 106 and 0.5 106) were melt blended with PP to investigate the effect of PDMS molecular weight (MW) on the morphology and mechanical properties of PP/PDMS blends. Scanning electron microscopic (SEM) examination showed that the size of PDMS domains was dependent on the MW of PDMS. It was found that the lower the value of PDMS MW, the better dispersion of the PDMS domains in the PP matrix. Tensile and Izod impact tests revealed that the addition of PDMS with lower MW would lead to a more significant increase in impact strength of the blends compared with the blends with higher MW ones, while the influence of the molecular weight on tensile strengths of the blends was relatively small in the MW range studied. Differential scanning calorimetry (DSC) results also showed that the crystallization temperature of PP was increased with decreasing PDMS MW, indicating a better nucleation capability of lower MW of PDMS. Melting flow rate (MFR) measurements indicated that the processibility of PP could be enhanced by adding PDMS, and again the lower MW PDMS resulted in better data. Our work demonstrates that not only the processibility but also the mechanical properties of PP could be enhanced to a more significant degree by using low MW PDMS than the higher ones.
A series of polydimethylsiloxane (PDMS) with varied molecular weights (Mw = 3 106, 1 106 and 0.5 106) were melt blended with PP to investigate the effect of PDMS molecular weight (MW) on the morphology and mechanical properties of PP/PDMS blends. Scanning electron microscopic (SEM) examination showed that the size of PDMS domains was dependent on the MW of PDMS. It was found that the lower the value of PDMS MW, the better dispersion of the PDMS domains in the PP matrix. Tensile and Izod impact tests revealed that the addition of PDMS with lower MW would lead to a more significant increase in impact strength of the blends compared with the blends with higher MW ones, while the influence of the molecular weight on tensile strengths of the blends was relatively small in the MW range studied. Differential scanning calorimetry (DSC) results also showed that the crystallization temperature of PP was increased with decreasing PDMS MW, indicating a better nucleation capability of lower MW of PDMS. Melting flow rate (MFR) measurements indicated that the processibility of PP could be enhanced by adding PDMS, and again the lower MW PDMS resulted in better data. Our work demonstrates that not only the processibility but also the mechanical properties of PP could be enhanced to a more significant degree by using low MW PDMS than the higher ones.
