Generation of novel hierarchical structures in long-range order in a phase-separated polymer blend by imposing a lateral temperature gradient

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 17350109
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Polymer/Textile materials
• Research Institution: Kyoto Institute of Technology
• Principal Investigator: SAKURAI Shinichi Kyoto Institute of Technology, Graduate School of Science and Technology, Associate Professor, 工芸科学研究科, 助教授 (90215682)
• Project Period (FY): 2005 – 2006
• Keywords: soft material / phase-contrast microscope / dissipative structure / convection / polymer blend / polymer solution / lateral temperature aradient / Soret effect

Research Abstract

We have reported micro-convections induced by the Soret effect in a polystyrene (PS)/dioctylphthalate (DOP) solution under a temperature gradient (heated from below). The Soret effect stands for the fact that the concentration gradient is induced under the applied temperature gradient. When temperature gradient is formed in a PS/DOP solution, PS is accumulated in the cooler side (upper side) by the Soret effect. Then the concentrated PS solution undergoes sedimentation because the density of PS is higher than DOP. Since this event can take place and result in a convective motion in a considerably thin layer of the solution (say 0.1 mm thickness), we refer to this as "micro-convection". Furthermore, it was found that convection was generated in PS/TCP solutions even when heated from above, instead of being heated from below. In addition we analyzed dark meshes of convection to obtain brightness of the dark meshes, based on which temporal changes in convection activity were examined. Som e oscillations were found in the plot of brightness as a function of time, and the brightness finally reached an asymptotic value. It is interesting to note that a similar behavior was seen for the case of a PS/DOP solution heated from bottom, although the direction of the energy input is opposed.
This study was further aimed at observation of the induced concentration gradients by the Soret effect under a phase-contrast microscope by imposing a lateral temperature gradient, which is free from convection because the induced concentration gradient is spread horizontally so that no inversion of the density in the solution will be vertically induced. For this purpose, we have produced a home-made sample holder with which the lateral temperature gradients were able to be imposed precisely. Using a liquid-crystalline compound (5CB), we have successfully conducted evaluation of the linearity of the temperature gradient as well as confirmation of the homogeneity of temperatures both in the vertical direction and in the other lateral direction. Generation of novel hierarchical structures in long-range order in a phase- separated polymer blend is now promisingly being studied.