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  • 21
    Electronic Resource
    Electronic Resource
    Monodisperse micron-sized crosslinked polystyrene particles. IV. Effect of network structure on polymerization procedure (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 1205-1209 
    Details
    ISSN: 1435-1536
    Keywords: Key words Monodisperse micron-sized polystyrene particles ; Urethane acrylate ; Particle diameter ; Particle number density ; Polymerization rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Monodisperse micron-sized polystyrene particles crosslinked using urethane acrylate were produced by dispersion polymerization in ethanol solution and the effect of the crosslinked network structure on the polymerization procedure was studied. The influences of the concentrations of the initiator and urethane acrylate on the particle diameter (D n), the particle number density (N p), and the polymerization rate (R p) were found to obey the approximate relationships D n ∝ [initiator]0.43 [urethane acrylate]0.05, N p ∝ [initiator]−1.30 [urethane acrylate]0.19, and R p ∝ [initiator]0.24 ± 0.02. The power-law dependence of D n and N p on the initiator concentration showed a similar trend to that of linear polystyrene reported in the literature. Especially, it was found that urethane acrylate does not have a serious effect on D n and N p of the particles produced. The dependence of R p on the initiator concentration was observed to be higher than that of linear polystyrene, suggesting that there is still competition between heterogeneous polymerization and solution polymerization because of the crosslinked network structure of the primary particle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050511
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  • 22
    Electronic Resource
    Electronic Resource
    Application of the Fermi Hypernetted-Chain theory and Effective Correlation Factor method for laughlin quantum Hall states (1997)
    Springer
    Journal of low temperature physics 108 (1997), S. 357-371 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Fermi Hypernetted-Chain theory and the Effective Correlation Factor method is applied to study the Laughlin states describing the fractional quantum Hall effect. Employing this formalism we evaluate the correlation energy, the radial distribution function, and the static structure factor, in the thermodynamic limit. The results obtained are similar to the boson Hypernetted-Chain treatment, usually adopted. The approach can be generalized to treat other correlated wave functions, such as wave functions of the composite fermion type for the fractional quantum Hall effect, in the thermodynamic limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02397679
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  • 23
    Electronic Resource
    Electronic Resource
    Highly monodisperse crosslinked polystyrene microparticles by dispersion polymerization (1998)
    Springer
    Colloid & polymer science 276 (1998), S. 870-878 
    Details
    ISSN: 1435-1536
    Keywords: Key words Highly monodisperse polystyrene microparticles ; the monomer-swellable surface ; long tetramethylene oxide groups ; the solubility of the monomer mixtures ; cloud points and fractional conversions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Highly monodisperse polystyrene microparticles cross-linked with urethane acrylates were produced by dispersion polymerization in ethanol solution in the presence of 2,2′-azobis (isobutyronitrile) initiator, polyvinylpyrrolidone stabilizer, and Aerosol–OT costabilizer. Different from conventional crosslinkers, the urethane acrylates employed as a crosslinker showed an excellent effect on maintaining the monodispersity of polystyrene microparticles even in the moderate crosslinker concentration. This was believed that the urethane acrylate helped forming the monomer-swellable surface of primary particles, because of its structurally long tetramethylene oxide groups in its molecule. However, at high concentration of the urethane acrylate, the rough surface and the coagulum of particles were observed, which was attributed to the seriously decreased solubility of the monomer mixtures in ethanol solution. The solubility of the mixtures of styrene monomer and urethane acrylate in the media had a serious effect on the average particle size and morphology of the final particles. This could be confirmed by the measurement of cloud points and fractional conversions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050323
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  • 24
    Electronic Resource
    Electronic Resource
    Morphology of micron-sized polystyrene particles crosslinked with urethane acrylate (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 210-216 
    Details
    ISSN: 1435-1536
    Keywords: Key words Morphology of micron-sized polystyrene particles ; Urethane acrylate crosslinker ; Monomer-swellable surface ; Medium solvency ; Nonspherical particles ; Asymmetric doublets
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The morphology of micron-sized polystyrene particles crosslinked with a urethane acrylate crosslinker was studied with different concentrations of urethane acrylate and medium solvency by means of simple dispersion polymerization. The urethane acrylate employed as a crosslinker showed an excellent effect on maintaining the monodispersity of the polystyrene particles at a moderate crosslinker concentration (to about 5 wt%) in terms of the monomer-swellable surface of primary particles. By enhancing the medium solvency, the amount of urethane acrylate incorporated was increased, while the monodispersity of the final particles was maintained. It was believed that the increase in solvency on adding xylene to ethanol solution helped the diffusion of the styrene monomers into the primary particles. At high concentration of urethane acrylate, however, nonspherical particles, ellipsoidal or egg-like singlets and asymmetric doublets, were observed. The increased crosslinking density seemed to repel the styrene monomers during particle growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00013745
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  • 25
    Electronic Resource
    Electronic Resource
    Highly monodisperse crosslinked polymethylmethacrylate microparticles by dispersion polymerization (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 66-72 
    Details
    ISSN: 1435-1536
    Keywords: Key words Highly monodisperse polymethylmethacrylate microparticles ; Carboxylic group-containing urethane acrylate ; Monomer-swellable surface ; Long tetramethylene oxide groups ; Lower polymerization rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Highly monodisperse polymethylmethacrylate (PMMA) microparticles crosslinked with carboxylic group-containing urethane acrylates (CUA) were produced by simple dispersion polymerization in methanol solution. In contrast to conventional crosslinkers, the CUA employed as a crosslinker was excellent for maintaining the monodispersity of PMMA microparticles even at moderate crosslinker concentrations (to about 5 wt%). It was believed that the CUA helped form the monomer-swellable surface of primary particles, because of the structurally long tetramethylene oxide groups in the molecule. Carboxylic groups in the molecular backbone resulted in larger primary particles by increasing the solubility of the monomer mixture in the medium. Owing to these larger primary particles, the crosslinked PMMA particles showed lower polymerization rates than the linear ones during particle growth. However, at high CUA concentrations (about 10 wt%), bimodal distributions were observed. This was attributed to the high crosslinking density of the primary particle surfaces. Therefore, monomer diffusion toward the polymer phase was restricted, resulting in more favorable secondary nucleation in the medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050368
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  • 26
    Electronic Resource
    Electronic Resource
    Poly(methyl methacrylate) hollow particles by water-in-oil-in-water emulsion polymerization (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 252-256 
    Details
    ISSN: 1435-1536
    Keywords: Key words Hollow structure ; Reactive viscosity enhancer ; Stable water-in-oil-in-water ; emulsion droplets ; Multi-hollow-structured particles ; Lyophilicity increase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Poly(methyl methacrylate) particles having hollow structures were produced by water-in-oil-in-water (W/O/W) emulsion polymerization where sorbitan monooleate (Span80) was used as a primary surfactant and sodium laurylsulfate and Glucopen (APG, polypeptide derivative) were used as secondary surfactants. Urethane acrylate having a molecular structure with a hard segment in the molecular backbone, a long soft segment in the middle, and vinyl groups at both ends was employed as a reactive viscosity enhancer. At low concentration of urethane acrylate, only a few particles contained a void in the polymer phase. However, as the concentration of urethane acrylate increased, the number of the particles containing the void increased. This was because urethane acrylate increased the viscosity of the monomer mixture and helped to form the stable W/O/W emulsion droplets, which possibly restricted droplet coalescence during emulsion polymerization. Moreover, at high concentration of urethane acrylate (above 7 wt%), multi-hollow-structured particles were obtained. It is believed that the increase in the lyophilicity of the monomer mixture caused by urethane acrylate led to stronger interfacial activity of the primary surfactant (Span80) and finally resulted in many internal aqueous droplets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00013751
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  • 27
    Electronic Resource
    Electronic Resource
    Mechanical properties of amphiphilic urethane acrylate ionomer hydrogels having heterophasic gel structure (1999)
    Springer
    Colloid & polymer science 277 (1999), S. 265-269 
    Details
    ISSN: 1435-1536
    Keywords: Key words Heterophasic gel structure ; Ionic hard domains ; Polyether soft domains ; Crystallinity ; Elastomeric properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Amphiphilic urethane acryale hydrogels containing ionic groups (dimethylolpropionic acid) were prepared by varying the molecular weight of the soft segment (polyether type) and the type of diisocyanate, and their mechanical properties were examined. They showed heterophasic gel structure composed of ionic hard domains induced by aggregation of the ionic groups and polyether soft domains comprising the urethane acrylate network. This heterophasic structure could be confirmed by dynamic mechanical analysis (DMA) and by wide-angle X-ray scattering analysis (WAXS); the crystallinity detected by WAXS and the transition peak of the ionic hard domains detected by DMA strongly suggested that there were ionic aggregates. These ionic aggregates acted as reinforcing fillers in the network, which eventually enhanced the tensile strength of the hydrogels. Above all, the tensile properties of the hydrogels were of interest in that the trends of the stress-strain curves were consistent with the rubbery ones. It is believed that the higher purity of the polyether soft domains resulted from the heterophasic gel structure imparting further elastomeric properties on the network.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00013754
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  • 28
    Electronic Resource
    Electronic Resource
    Ground-state correlations and finite temperature properties of the transverse Ising model (2005)
    Springer
    The European physical journal 43 (2005), S. 373-378 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. We present a semi-analytic study of Ising spins on a simple square or cubic lattice coupled to a transverse magnetic field of variable strength. The formal analysis employs correlated basis functions (CBF) theory to investigate the properties of the corresponding N-body ground and excited states. For these states we discuss two different ansaetze of correlated trial wave functions and associated longitudinal and transverse excitation modes. The formalism is then generalized to describe the spin system at nonzero temperatures with the help of a suitable functional approximating the Helmholtz free energy. To test the quality of the functional in a first step we perform numerical calculations within the extended formalism but ignore spatial correlations. Numerical results are reported on the energies of the longitudinal and the transverse excitation modes at zero temperature, on critical data at finite temperatures, and on the optimized spontaneous magnetization as a function of temperature and external field strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2005-00066-x
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  • 29
    Electronic Resource
    Electronic Resource
    Electrorheological characteristics of polyaniline and its copolymer suspensions with ionic and nonionic substituents (2000)
    Springer
    Colloid & polymer science 278 (2000), S. 61-64 
    Details
    ISSN: 1435-1536
    Keywords: Key words Electrorheological fluid ; N-substituted copolyaniline ; Polyaniline ; Poly(aniline-co-o-ethoxyaniline)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electrorheological (ER) characteristics of ER fluids, composed of suspensions of semiconducting polyaniline and two different copolyaniline particles in silicone oil, were determined experimentally. Ionic sodium diphenylamine sulfonate and nonionic o-ethoxyaniline were used to synthesize copolyanilines, i.e. N-substituted copolyaniline and poly(aniline-co-o-ethoxyaniline), respectively. ER fluids composed of these three different polymers were compared with respect to their rheological properties under an applied electric field. It was found that ER fluids containing a copolymer with an ionic group exhibited the highest ER performance among polyaniline and its copolymer systems in a shear-rate region above 1 s−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050009
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  • 30
    Electronic Resource
    Electronic Resource
    Monodisperse micron-sized cross-linked polystyrene particles. VI. Understanding of nucleated particle formation and particle growth (2000)
    Springer
    Colloid & polymer science 278 (2000), S. 591-594 
    Details
    ISSN: 1435-1536
    Keywords: Key words Nucleated particle formation ; Urethane acrylate ; Turbidity measurement ; Boundary concentration ; Stage of particle growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The procedure of nucleated particle formation and particle growth in dispersion polymerization was studied with the intention of understanding the production of monodisperse polystyrene particles cross-linked with urethane acrylate (UA). The time required for the formation of primary particles was determined exactly from the turbidity measurement of the reaction mixture with the polymerization time. It could be found that differing from conventional divinyl cross-linkers, such as divinylbenzene, UA had a boundary concentration where the association and coagulation of preformed nuclei with other oligomers and/or nuclei effectively took place until the primary particle formed. Similarly to linear polystyrene particles, the particle number density of the primary particles cross-linked with UA remained constant to the final particles. This observation verifies the suggestion that the primary particles cross-linked with UA readily absorbed the monomers from the medium during the stage of particle growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003960050561
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