Architecture of colloidal crystals constructed by silica hybrid nanoparticles

Silica (SiO₂)‐crosslinked polystyrene (PS) particles possessing photofunctional N,N‐diethyldithiocarbamate (DC) groups on their surface were prepared by the free‐radical emulsion copolymerization of a mixture of SiO₂ (diameter D_n = 192 nm), styrene, divinyl benzene, 4‐vinylbenzyl N,N‐diethyldithiocarbamate (VBDC), and 2‐hydroxyethyl methacrylate with a radical initiator under UV irradiation. In this copolymerization, the inimer VBDC had the formation of a hyperbranched structure by a living radical mechanism. These particles had DC groups on their surface. Subsequently, poly(methyl methacrylate) brushes encapsulated SiO₂ particles were synthesized by the grafting from a photoinduced atom transfer radical polymerization (ATRP) approach of methyl methacrylate initiated by SiO₂‐crosslinked PS particles as a macroinitiator. We constructed the colloidal crystals using these photofunctional particles. Moreover, the SiO₂ particle array of colloidal crystals was locked by radical photopolymerization with vinyl monomer as a matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Numerical analysis of active magnetic regenerators for hydrogen magnetic refrigeration between 20 and 77 K

A model active magnetic regenerator refrigerator (AMR) with the Brayton-like operation cycle was analyzed by numerical cycle simulation in the temperature range between 20 and 77 K. In order to study the performance using magnetic material with various transition temperatures T_c, entropy of magnetic material with second order phase transition was calculated using mean field theory and Debye approximation. The cooling performance is shown to be high when the heat exhaust temperature is close to the transition temperature. It is shown that the optimized operation condition depends on both T_c and operation temperatures. Multi-layered AMR beds were shown to improve the performance of AMR. Multi-stage AMR was also discussed.     

Highly flame retardant coating consisting of starch and amorphous sodium polyborate

Mixture of starch and amorphous sodium polyborate (SPB) is found to show high flame retardancy, when its aqueous solution is deposited and dried on organic polymer materials such as polyethylene terephthalate (PET) nonwoven, rigid polyurethane (RPU) foam, and polypropylene (PP) nonwoven. The PET nonwoven (10 mm thickness) and the RPU foam (10 mm thickness) coated with the mixture endure the premixed flame of butane gas burner with length of 100 mm for more than 12 min. The PP nonwoven (0.7 mm thickness) endures the nonpremixed flame with length of 65 mm in the 45 degrees Meckel burner test for more than 2 min. The backside temperatures in the both tests remain below 130 °C. The thermal analyses and the SEM observation indicate the mechanism that the SPB foam promotes the carbonization of starch and that the carbonized layer together with the SPB foam insulate inside from oxygen and heat.     

Metal-free isotactic-specific radical polymerization of N-isopropylacrylamide with pyridine N-oxide derivatives: The effect of methyl substituents of pyridine N-oxide on the isotactic specificity and the proposed mechanism for the isotactic-specific radical polymerization

The radical polymerizations of N-isopropylacrylamide (NIPAAm) in chloroform at low temperatures in the presence of pyridine N-oxide (PNO) derivatives were investigated. It was found that the methylation at meta-positions of PNO improved the isotactic specificity induced by PNO, whereas the methylation at ortho-positions prevented the induction of the isotactic specificity. NMR analysis revealed that NIPAAm and PNO derivatives formed predominantly 2:1 complex through a hydrogen-bonding interaction. Furthermore, the induction of the isotactic specificity was attributed to the conformationally limited propagating radicals. Based on these findings, the mechanism of the isotactic-specific radical polymerization was discussed.     

Technology in emulsified particle size control by new mixing method

The best pulverization of emulsions that can be achieved using conventional mixing blades is in the micrometer realm. Now, with our new 'thin-film spin system' high-speed mixer, it is possible to attain pulverization in the nanometer realm. The particle size distribution can now be controlled to achieve an almost single distribution state. Particles can be pulverized without being severed, preventing secondary agglomeration after processing. This new mixing system also solves many of the problems common to conventional pulverization processes.     

Architecture of prototype copolymer brushes composed of alternating structure and intramolecular phase separation of side chains in solution

Atom transfer radical polymerization (ATRP) was applied to the synthesis of prototype copolymer brushes composed polystyrene/poly(t‐butyl methacrylate) (PS/PBMA) alternating structure. Dilute solution properties of prototype copolymer brush were investigated by static and dynamic light scattering (SLS and DLS) in tetrahydrofuran (THF). As a result, such prototype copolymer brush composed of short aspect ratio formed a star‐like single molecule in THF. To discuss the intramolecular phase separation of PS/PBMA brushes in solution, we determined the radius of gyration (R_g) and cross‐sectional radius of gyration (R_g,c) of prototype copolymer brush by small‐angle X‐ray scattering (SAXS) using Guinier's plots in THF and styrene. We used styrene as solvent to cancel each other out with the electron density of PS side chains. Both R_g and R_g,c obtained in styrene decreased drastically compared with those obtained in THF. These results indicated strongly that PS and PBMA side chains of prototype brushes formed intramolecular phase separation even in good solvent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010