HASHIMOTO Polymer Phasing


Research Director: Dr. Takeji Hashimoto
(Professor, Graduate School of Engineering, Kyoto University)
Research Term: 1993~1998


"Polymer Phasing" was coined to refer to studies of mesoscopic pattern formation in self-organization processes via phase transitions and phase separation in polymer systems as a model for complex liquids. The basic objective was to explore the space-time organization processes through both in situ and real-time experimental observations and theoretical computer simulations, resulting in the proposal of new materials with novel structures. Polymer blends, block copolymers, gels and ionic colloidal dispersions were employed as model systems having large and long fundamental lengths and time scales. As a challenging problem in open non-equilibrium systems, how external fields such as shear flow, stationary or moving temperature gradients and chemical reaction affect the self-organization processes was also studied.

Research Results

Phase-separation process in polymer mixtures: For the first time, 3D digital images of phase-separating binary polymer mixtures were constructed with nearly equal phase volumes and nearly equal molecular weights. The images were found to be bicontinuous, and to have characteristics of a "sponge-like" structure found for microemulsions. This research has contributed to the field of critical phenomena: the sponge-like structure was proven to be a real-space structure for phase-separating binary mixtures of simple liquids.

Organization of block copolymers: A high-resolution small-angle-X-ray scattering analysis was applied to explore the order-disorder transition.
 (ODT) of block copolymers using a specially constructed Bonse-Hart type apparatus (USAXS). The analysis led to the discovery of a biphase region, where ordered and disordered phases coexist at thermal equilibrium around the ODT temperature.

Phase behavior of colloidal dispersions: Aqueous dispersions of ionic colloidal particles were investigated from the viewpoint of phase transitions and the self-organization of supermolecules. The ordered, disordered, order-disorder coexistence, and gas-liquid coexistence phases were found in the space determined by the salt concentration, particle charge density and particle concentration.

Internal structure of polymer gels: A chemical gel is a cross-linked three-dimensional polymer network swollen by a fluid. An intriguing hierarchy structure which developed in a macroscopically homogeneous poly (N-isopropylacrylamide) gel prepared via a chemical reaction was clarified. It visualized for the first time a sponge-like structure comprising both network-rich and network-poor phases with an average spacing of ca. 10 mm.

Nano-processing method developed: Novel nano-scale structures were developed utilizing the microphase separation of block copolymers. A method was developed to selectively degrade one of the microdomains to create unique materials containing regularly spaced networks of holes. These holes were further plated with metals to produce polymer/metal hybrids. Hybrid structures were also developed by introducing metal nanoparticles selectively into one of the nanodomains.


·Pattern A Interfaces developed by phase separation via spinodal decomposition between the two coexisting phases in binary fluid mixtures. The two biocontinuous phases exist in both sides of interfaces colored by red and green. The interfaces have a negative Gaussian curvature, and the two phases have equilibrium compositions. The pattern is obtained by a computer simulation using the time-dependent Ginzburg-Landau equation.


·Pattern B "Void" structure in dilute aqueous colloidal dispersions observed by a confocal laser scanning microscope. The coexistence of a spherical dense region and a less dense region is observed. This self-organized structure presents provocative analogies to the bicontinuous polymer structure shown in Pattern A. Sphere diam.: 0.12 µm, sphere conc.: 0.1vol%

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