Confinement Effects on Chain and Glass Dynamics in Immiscible Polymer Blends

摘要

Dynamics of two-component polymer systems such as blends, copolymers, and nanocomposites, are complicated and not well understood at a fundamental level. It is clear from experimental evidence that the effect of one component on the dynamics of the second is nontrivial. For example, in contrast with wellentangled homopolymer melts, miscible polymer blends often show a dramatic failure of time-temperature superposition (tTS) principle, and very broad glass transitions are typically observed. It is generally accepted that these macroscopic observations are a result of distinct dynamics of the blends components, since each component experiences a different local friction from that of the pure polymer.Among the variousmodels that attempt to predict miscible blend component dynamics, the self-concentration model proposed by Lodge and McLeish9 has received considerable attention recently. On the other hand, most investigations on immiscible blends have only focused on droplet breakup dynamics, but their molecular dynamics have received very little attention. We have designed a series of immiscible model blends wherein a small fraction of __probe__ chains is dispersed in a very high-molecular weight (MW) phase-separated matrix, as a heretofore uninvestigated model system, in order to examine the impact of confinement from the matrix on the terminal and glass dynamics of the probe. Current theories10 suggest that confinement effects are expected when length scales are below 10 times the mean-square end-to-end distance 01/2 usually ranging from 10 to 30 nm. However, we have observed a strong confinement effect formicrometer-size dispersed droplets, which is much larger than this estimated critical dimension (10_01/2).