Satoshi Akasaka

Helical Nanocomposites from Chiral Block Copolymer Templates

Three-dimensional hexagonally packed PLLA nanohelices in the PS matrix were formed in the self-assembly of PS-PLLA chiral block copolymer. After hydrolysis of the PLLA blocks, PS with hexagonally packed helical nanochannels can be fabricated and treated as the template for the following sol-gel process. Subsequently, silica precursor mixture was introduced into the PS template by a pore-filling process. Well-defined helical nanocomposites with SiO(2) inorganic nanohelices orderly dispersed in polymeric matrix can be successfully obtained after the sol-gel process. As a result, with the combination of the self-assembly of degradable block copolymers and sol-gel chemistry, we suggest a novel method for the preparation of the helical nanocomposites with ordered texture.

Block Copolymers with a Twist

Chiral block copolymers (BCPs*) comprising chiral entities were designed to fabricate helical architectures (i.e., twisted morphologies) from self-assembly. A new helical phase (H*) with P622 symmetry was discovered in the self-assembly of poly(styrene)-b-poly(l-lactide) (PS-PLLA) BCPs*. Hexagonally packed, interdigitated PLLA helical microdomains in a PS matrix were directly visualized by electron tomography. The phase diagram of the PS-PLLA BCPs* was also established. Phase transitions from the H* phase to the stable cylinder and gyroid phases were found after long-time annealing, suggesting that the H* is a long-lived metastable phase. In contrast to racemic poly(styrene)-b-poly(d,l-lactide) BCPs, chiral interaction significantly enhances the incompatibility between achiral PS and chiral PLLA blocks in the PS-PLLA BCPs* and can be estimated through the determination of the interaction parameter.

Nonlinear optical properties of gold nanoparticles selectively introduced into the periodic microdomains of block copolymers.

Nonlinear-optical nanocomposite materials with a photonic crystal structure were fabricated using block copolymers and gold nanoparticles. By dispersing the gold nanoparticles into the selective microdomains of the block copolymers, we could achieve the enhancement of nonlinear optical properties as revealed by the Z-scan technique. The optical nonlinearities were enhanced by the local field effect and the effect of the periodic distribution of the microdomains filled with gold nanoparticles. Furthermore, the highest optical nonlinearity was achieved by matching the domain spacing of the copolymers with the frequency of the surface plasmon resonance peak of the gold.

Scattering studies of novel degradable block copolymers of strong segregation class

Abstract We have investigated microdomain structures of novel block copolymers, poly(p-tert-pentyloxyvinylbebzene-b-p-vinylphenol) and poly(p-tert-pentyloxy-vinylbebzene-b-p-vinylphenol-b-p-tert-pentyloxyvinylbebzene) with small-angle X-ray scattering (SAXS). We analyzed SAXS profiles of the block copolymers in their ordered state with paracrystal theory, and found that the block copolymers formed the lamella structures in the order of 1 nm with long-range order. We estimated the lower-limit size of the microdomain structure by analyzing the order–disorder transition of the block copolymer solutions and explored that we can attain 7.6 nm by decreasing the molecular weight of block copolymers.