Dynamic Processes in Complex Polymeric Systems.

[摘要] In general, the physical properties of polymers intimately depend on the morphology. In this dissertation we investigated the role of morphology on dynamic processes that occur in complex systems possessing appreciably different morphologies: (1) diblock copolymer/homopolymer blends; (2) miscible blends of linear chain polymers; (3) semicrystalline polymer.(i) A-b-B diblock copolymer chains form micelles of A-type coronas and B-type cores, in an A-type host. We investigated the segmental dynamics of polyisoprene (PI) chains in polystyrene-b-polyisoprene (PS-b-PI) melt as well as PS-b-PI/polystyrene (PS) blends. PS-b-PI forms micellar structures of varying geometries within PS hosts of different molecular weight. The glass transition temperatures and dynamics of PI were more strongly influenced by the local geometry than by the dimensions of confinement. The behavior is rationalized in terms of the notion of free volume.(ii) The segmental dynamics of poly(vinyl methyl ether) (PVME) chains in miscible blends of PVME/PS were investigated. These blends are known to be locally compositional heterogeneous. We showed, for the first time, the temperature dependence of the heterogeneity by measuring their dynamics: the PS and PVME chains are mixed more homogeneously at high temperatures, whereas at low temperatures the behavior is indicative of PVME chains relaxing in two distinctly local compositions.(iii) The effect of morphology of a hole-conducting semicrystalline polymer was studied. We showed that the out-of-plane hole transport in conjugated polymer films, poly(3-hexylthiophene) (P3HT), is very sensitive to the morphology of the polymer. Impedance spectroscopy conducted the measurement, which simultaneously extracted the dc conductivity, mobility and carrier density. The out-of-plane carrier mobility of P3HT increases with increasing thickness from 100 nm to ~700 nm, meanwhile the dc conductivity and the carrier density decrease dramatically with thickness in the same range. Such dramatic trends are due to the substrate induced orientation of the crystalline domains in P3HT; unlike the inorganic scenarios, in conjugated polymers the carrier mobility and density are no longer intrinsic properties and can be strongly influenced by the surrounding environment.The studies of these systems provide new insights into the role of morphology on diverse dynamic processes that occur in polymers.

[发布机构] University of Michigan

[效力级别] Polymer Dynamics

[关键词] Polymer Physics;Polymer Dynamics;Structure/Property Relationship;Broadband Dielectric Spectroscopy;Complex Polymeric System;Charge Transport Process;Physics;Science;Physics