Time variation of the relaxation phenomena of polymer blends during the phase separation by time resolved dielectric relaxation spectroscopy

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In order to understand the relation between morphology and properties of binary polymer blends, we performed dielectric measurements on several systems, such as miscible blends and phase separated systems: (1) Polystyrene / Poly(vinyl methyl ether) (PS/PVME), (2) Polyisoprene / Poly(vinyl ethylene), (3) Poly(vinyl acetate) / Poly(ethylene oxide), (4) Polystyrene / 4-cyano,4'-alkyl biphenyl. The common characteristic of these blends is that there exists large difference in the component glass transition temperatures (Tg). In all the blends except for system (3), dynamical heterogeneity was observed in the dielectric relaxation behaviors.We examined the time variation of dielectric relaxation behavior for a PS/PVME blend after inducing phase separation. The result was that the peak frequency corresponding to the segmental motion of the PS component shifted to the low frequency side and the height of the peak gradually increased just after the phase separation. As for the reason of the peak shift, we think that the enrichment of PS (high Tg component) concentration due to the growth of phase structures increased the friction factor for PS segments. The reason for the increase of the peak height might be explained as follows: The fraction of the PS existing near the interface between PS-rich and PVME-rich domain will decrease while that of PS existing in the middle of the PS-rich domain will increase during the phase separation. If the observed a-peak is ascribable to the segmental motion of PS inside the PS domain, its intensity (corresponding to the peak height) will increase with time. For PS/ 4-cyano, 4'-pentylbiphenyi blend, the change of the relaxation behavior during the phase separation was investigated. In this experiment we observed new relaxation process which can not be explained in terms of the relaxations inherent to the component dynamics. We could assign this to the Maxwell-Wagner type relaxation.