Study On The Phase-Separated Structures Of Polymer Composites With Modulus Inhomogeneity

In this paper, the phase separation mechanism of polymer composites with modulus inhomogeneity was investigated by using computer simulation in a framework of pattern dynamics, through which the formation of phase structures of dodecylbenzene sulfonic acid doped polyaniline/ polyacrylonitrile blends (PANI-DBSA/PAN) was interpreted.PANI-DBSA was obtained through emulsion polymerization from aniline in water-chloroform-DBSA system with amine ammonium persulphate acting as oxidant and DBSA as emulsifiter and doping agent simultaneously. The PANI-DBSA/PAN blend films were obtained by using solution cast. The conductivities of the blend films were tested and their phase morphologies were also investigated by means of OM, SEM, and DMA. On the other hand, the PANI-DBSA/PAN blend fibers were also prepared via conventional wet spinning technique for PAN fiber. It was found that PANI-DBSA/PAN blend films showed good conductivities and the conductive percolation threshold of lay at 4 wt% of PANI-DBSA. The blend films possessed the so-called skin-core structures, i.e., in the skin layer PANI-DBSA dispersed as connective networks while in the core layer as isolated droplets. It could be concluded from the DMA analysis that the modulus of PAN was higher than that of PANI-DBSA. Moreover, the conductivities of PANI-DBSA/PAN blend films were prior to those of PANI-DBSA/PAN blend fibers.The kinetic model for the phase separation of polymer composites with modulus inhomogeneity was established by incorporating the coupling between compositional order parameter and elastic field, and the motion equation was numerically solved by using cell dynamical system. The results of computer simulation showed that the phase-inversed structures would be formed in such blend system, i.e., the soft minorityphase could form connective structures in hard phase matrix, which was far different from the phase separation mechanism of conventional polymer blends. However, the formation of PANI-DBSA networks in PAN matrix could be well understood along such phase-inversed mechanism.By modeling the formation processes of PANI-DBSA/PAN blend films with directional quench, the skin-core structures of the blend films were also explain basing on the kinetic model mentioned above.The phase separation processes under external stress field of polymer blends with modulus inhomogeneity were also investigated. The computer simulation results showed that it was easy for the orientational layer structures but difficult for the networks formed in such blend system. Therefore, it was reasonable that the conductivities of PANI-DBSA/PAN blend films were prior to those of PANI-DBSA/PAN blend fibers, because the external stress fields were involved in the formation processes of the blend fibers.