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2003 Volume 21 Issue 6
2003, 21(6): 587-602
Abstract:
An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added topolymeric materials for improving their mechanical performance using existing compounding techniques. The followingitems are discussed in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles duringirradiation, (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultantcomposites, and (c) possible morphological changes induced by the addition of nanoparticles.Through irradiation grafting polymerization,nanoparticle agglomerates turn into a nano-composite microstructure(comprised of the nanoparticles and the grafted,homopolymerized secondary polymer),which in turn builds up a strong interfacial interaction with the surrounding,primary polymeric matrix during the subsequent mixing procedure.Due to the fact that different grafting polymers brought about different nanoparticle/matrix interfacial features,microstructures and properties of the ultimate composites could thus be tailored.It was found that the reinforcing and toughening effects of the nanoparticles on the polymer matrix can be fully brought into play at a rather low filler loading in comparison to conventional particulate filled composites.
An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added topolymeric materials for improving their mechanical performance using existing compounding techniques. The followingitems are discussed in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles duringirradiation, (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultantcomposites, and (c) possible morphological changes induced by the addition of nanoparticles.Through irradiation grafting polymerization,nanoparticle agglomerates turn into a nano-composite microstructure(comprised of the nanoparticles and the grafted,homopolymerized secondary polymer),which in turn builds up a strong interfacial interaction with the surrounding,primary polymeric matrix during the subsequent mixing procedure.Due to the fact that different grafting polymers brought about different nanoparticle/matrix interfacial features,microstructures and properties of the ultimate composites could thus be tailored.It was found that the reinforcing and toughening effects of the nanoparticles on the polymer matrix can be fully brought into play at a rather low filler loading in comparison to conventional particulate filled composites.
2003, 21(6): 603-608
Abstract:
Water soluble conducting polyaniline with electrical conductivity of 10-1-10-2 S/cm was prepared employingdopant induced water solubility technology. The water resistance of the conducting film was significantly improvedemploying sol-gel hybrids method, especially when the conductive polyaniline loading was below 30 wt%. The reason forthe improvement is that the conducting polyaniline chains are confined in a stable inorganic network.
Water soluble conducting polyaniline with electrical conductivity of 10-1-10-2 S/cm was prepared employingdopant induced water solubility technology. The water resistance of the conducting film was significantly improvedemploying sol-gel hybrids method, especially when the conductive polyaniline loading was below 30 wt%. The reason forthe improvement is that the conducting polyaniline chains are confined in a stable inorganic network.
2003, 21(6): 609-620
Abstract:
Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observedwith fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB),dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C12E8) wereallowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalenelabeled copolymers. The relative excimer emission intensity IE/IM of a cationic probe 1-pyrenemethylamine hydrochloride(PyMeAHCl) and the non-radiative energy transfer(NRET)Ipy/INp of naphthalene to pyrene for labeled polyelectrolytes were chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes.The 1:1aggregation of polyelectrolyte-CTAB with respect to the change was found as long as the CTAB concentration was slightly higher than its critical aggregation concentration (CAC).The intermolecular NRET indicated that the CTAB-bound polyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails.However,neither 1:1 polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to its weaker hydrophobicity of 12 carbon atoms in the tail,which is shorter than that of CTAB.As known from the fluorescence results,nonionic surfactant C12E8 did not bind on the anionic polyelectrolytes,but the presence of PAMPS promoted the micelle fromation for C12E8 at the CAC slightly below its critical micelle concentration(CMC).The solid complex of dansyl labeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of the polyelectrolyte or with alkane tail length of the surfactant.SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC,respectively.
Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observedwith fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB),dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C12E8) wereallowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalenelabeled copolymers. The relative excimer emission intensity IE/IM of a cationic probe 1-pyrenemethylamine hydrochloride(PyMeAHCl) and the non-radiative energy transfer(NRET)Ipy/INp of naphthalene to pyrene for labeled polyelectrolytes were chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes.The 1:1aggregation of polyelectrolyte-CTAB with respect to the change was found as long as the CTAB concentration was slightly higher than its critical aggregation concentration (CAC).The intermolecular NRET indicated that the CTAB-bound polyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails.However,neither 1:1 polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to its weaker hydrophobicity of 12 carbon atoms in the tail,which is shorter than that of CTAB.As known from the fluorescence results,nonionic surfactant C12E8 did not bind on the anionic polyelectrolytes,but the presence of PAMPS promoted the micelle fromation for C12E8 at the CAC slightly below its critical micelle concentration(CMC).The solid complex of dansyl labeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of the polyelectrolyte or with alkane tail length of the surfactant.SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC,respectively.
2003, 21(6): 621-629
Abstract:
Discussion is presented on the use of the photoisomerization of azobenzene chromophore in the design andpreparation of novel functional materials. The two systems reviewed are azobenzene polymer-stabilized liquid crystals andazobenzene elastomers. In the first case, a polymer network containing azobenzene moieties is used to optically induce andstabilize a long-range liquid crystal orientation without the need of treating the surfaces of the substrates. This optical and rubbing-free approach was applied to nematic and ferroelectric liquid crystals.In the second case,an azobenzene side-chain liquid crystalline polymer is grafted onto a styrene-butadiene-styrene triblock copolymer to yield a photoactive thermolastic elastomer.Coupled mechanical and optical effects make possible the formation of diffraction gratings that may be useful for mechanically tunable optical devices.
Discussion is presented on the use of the photoisomerization of azobenzene chromophore in the design andpreparation of novel functional materials. The two systems reviewed are azobenzene polymer-stabilized liquid crystals andazobenzene elastomers. In the first case, a polymer network containing azobenzene moieties is used to optically induce andstabilize a long-range liquid crystal orientation without the need of treating the surfaces of the substrates. This optical and rubbing-free approach was applied to nematic and ferroelectric liquid crystals.In the second case,an azobenzene side-chain liquid crystalline polymer is grafted onto a styrene-butadiene-styrene triblock copolymer to yield a photoactive thermolastic elastomer.Coupled mechanical and optical effects make possible the formation of diffraction gratings that may be useful for mechanically tunable optical devices.
2003, 21(6): 631-637
Abstract:
A simple method for the fabrication of ultrathin films containing low molecular weight dye material is introduced(post-adsorption technique). The chromophore used is 4-nitro-4'-decyloxy azobenzene quaternary ammonium salt (azo-10Q).In classical layer-by-layer (LBL) procedures, where the substrate is dipped alternately into the chromophore solution and thecomplementary polyelectrolyte, the chromophore tends to desorb from the film during subsequent immersion in thepolyanion solution, and there is little or no indication of multilayer growth.The extent of desorption depends somewhat on the selection of polyelectrolyte,the ionic strength and the pH of solution.An alternative approach is to first prepare conventional LBL films from a pair of oppositely charged polyelectrolytes,and then to soak this film into the chromophore solution,where adsorption by penetration into the LBL film may take place.In preliminary results,a linear dependence of UV absorbance on layer number of LBL film thus prepared was found,demonstrating the apparent effectiveness of the post-adsorption technique for the preparation of azo-10Q-containing ultrathin films.
A simple method for the fabrication of ultrathin films containing low molecular weight dye material is introduced(post-adsorption technique). The chromophore used is 4-nitro-4'-decyloxy azobenzene quaternary ammonium salt (azo-10Q).In classical layer-by-layer (LBL) procedures, where the substrate is dipped alternately into the chromophore solution and thecomplementary polyelectrolyte, the chromophore tends to desorb from the film during subsequent immersion in thepolyanion solution, and there is little or no indication of multilayer growth.The extent of desorption depends somewhat on the selection of polyelectrolyte,the ionic strength and the pH of solution.An alternative approach is to first prepare conventional LBL films from a pair of oppositely charged polyelectrolytes,and then to soak this film into the chromophore solution,where adsorption by penetration into the LBL film may take place.In preliminary results,a linear dependence of UV absorbance on layer number of LBL film thus prepared was found,demonstrating the apparent effectiveness of the post-adsorption technique for the preparation of azo-10Q-containing ultrathin films.
2003, 21(6): 639-651
Abstract:
A review is given of grafting-from methods using living polymerizations, with emphasis on grafting from polymermicrospheres using ATRP.
A review is given of grafting-from methods using living polymerizations, with emphasis on grafting from polymermicrospheres using ATRP.
