No abstract

Gel formation was discovered in an aqueous mixture of enantiomeric triblock copolymers, PLLA‐PEG‐PLLA and PDLA‐PEG‐PDLA. This system is characteristic in that an interesting sol–gel transition was induced by the stereo‐complexation of the PLLA and PDLA segments of the block copolymers around 37°C. The process of gel formation was clearly monitored by the rheological change, and the responsibility of the stereo‐complex formation for the gelation was confirmed by wide‐angle X‐ray scattering. The mechanism of this gel formation is discussed in relation to its potential applications.

Explosive crystallization (EC) takes place during flash lamp annealing in micrometer-thick amorphous Si (a-Si) films deposited on glass substrates. The EC starts from the edges of the a-Si films due to additional heating from flash lamp light. This is followed by lateral crystallization with a velocity on the order of m/s, leaving behind periodic microstructures in which regions containing several hundreds of nm-ordered grains and regions consisting of only 10-nm-sized fine grains alternatively appear. The formation of the dense grains can be understood as explosive solid-phase nucleation, whereas the several hundreds of nanometer-sized grains, stretched in the lateral direction, are probably formed through explosive liquid-phase epitaxy. This phenomenon will be applied to the high-throughput formation of thick poly-Si films for solar cells.

Enantiomeric poly(lactide)s were assembled on a quartz crystal microbalance (QCM) substrate, which detects the mass of the polymers from the frequency shift, following immersion of QCM into alternating acetonitrile solutions. A quantitative QCM analysis at each step and a differential scanning calorimetric study of the assembly showed racemic crystal (stereocomplex) formation on the substrate surface. Atomic force microscopic observation showed a dotted nanostructure of the assembly. The assembly amount was increased with increasing the PLA concentration and the immersion time, while that was decreased with increasing the assembly temperature. The heterogeneous assembly was also prepared by altering the immersion time. We found that racemic crystal formation was applied to the alternate deposition of certain structurally regulated polymers.