Phase equilibrium of poly(n-butyl acrylate) and E7

The experimental equilibrium phase diagram of mixtures of linear poly(n-but yl acrylate) of molecular mass M-w = 112 000 g mol(-1) and the low molecula r mass LC mixture E7 has been established using polarized optical microscop y and light scattering techniques. The diagram is found to be reminiscent o f an upper critical solution temperature system. Two independent series of samples with the same composition were studied, yielding consistent results . A region of nematic and isotropic coexisting phases and a region of a sin gle isotropic phase were identified in the composition-temperature phase di agram. The results were analysed within a theoretical model combining the F lory-Huggins lattice theory for isotropic mixing and the Maier-Saupe theory for nematic ordering. Interestingly, no region of isotropic coexisting pha ses was observed in our experiments. This is probably due to the fact that the nematic interaction overwhelms the isotropic interaction in the region where (I + I) coexisting phases could appear. A preferential solubility of certain constituents of the LC mixture in the polymer could possibly be a r eason for this behaviour.