ABSTRACT
The phase separation processes of polymer blends under external field, such as photochemical reaction, (oscillatory) shear deformation, have been studied. In the present session, phase separation of photo-reactive polymer blends was presented by Endoh et al. (2726, E741). They examined the effects of photo-crosslinking and reversible photoisomerization induced by linearly polarized light on the phase separation processes of a mixture of polystyrene and poly (vinyl methyl ether) (PVME). Polystyrene labelled with anthracene (PSS) and that labelled with transstilbene were used for cross-linking and photoisomerization, respectively. Upon irradiation, the blend underwent anisotropic phase separation, exhibiting lamellar and weakly-anisotropic structures for photo-crosslinked and photoisomerized mixtures, respectively. In the case of cross-links, the phase separation along the polarized direction was strongly suppressed compared to the direction perpendicular to the polarization (see Figure 2). On the other hand, in the case of photoisomerization, the phase separation was most promoted in the parallel direction. The (frozen) anisotropy observed in the PSS/PVME blend under irradiation with linearly polarized light was not observed when the phasse separation temperature was set above the glass transition temperature (T1) of PSS. This results imply that, at temperatures lower than T1 of the PSS, relaxation of the anisotropy of the PSS-rich domains was slower than the rate of the phase separation. These results also suggest an existence of a mode-selection process driven by the interference of instabilities growing with different rates at different orientation in the mixtures.
