Interfacial Properties for liquid-crystalline Polymer solutions

点击翻译按钮获取中文摘要

In this research project, we have dealt with properties of interface between coexisting isotropic and liquid-crystal phases of lyotropic liquid-crystalline polymer solutions.Our utmost concern was to examine (1) the molecular alignment in the anisotropic phase near the isotropic-anisotropic interface, (2) the dependence of the interfacial tension on chain length, and (3) the dependence of the interfacial tension on chain stiffness.We have chosen well characterized rigid and semiflexible polymers, schizophyllan (a triple-helical polysaccharide), poly(n-hexyl isocyanate) (PHIC), and poly(n-butyl isocyanate) (PBIC), whose bulk solution properties have been studied in detail.(1) The isotropic-liquid-crystal interface was observed by a polarizing microscope with a compensator oriented at 45ﾟ to the directions of the crossed polarizers, and the observations revealed that rigid polymer molecules align themselves parallel to the interface.(2) The interfacial tension between coexisting isotropic and liquid-crystal phases of solutions of schizophyllan, PHIC, and PHIC/PBIC mixtures was measured by the sessile or pendant drop method.For schizophyllan solutions, the interfacial tension is almost inversely proportional to the polymer molecular weight.On the other hand, the interfacial tension for PHIC solutions is almost independent of the polymer molecular weight The former molecular weight dependence agrees with the prediction of theories for rodlike polymer solutions, and the latter molecular weight independence is consistent with the prediction of a theory for wormlike-chain solutions in the coil limit.It is known that PHIC is more flexible than schizophyllan.We also found that the interfacial tension strongly depends on the molecular weight distribution and addition of chemically different polymer species.