Structure-Property Relations for Polymer Interfaces

9505599 Fredrickson随着强大的新的表面表征技术的出现，许多实验组已经报道了多组分聚合物共混物以及嵌段和无规共聚物的表面分离和润湿行为。通常认为组分之间的表面能差异是产生此类系统中的不均匀组合物分布的原因。然而，最近对模型聚烯烃共混物和共聚物的实验已经表明，界面热力学与构象性质的差异之间存在强相关性（即，骨干的灵活性）的组件，导致另一种熵的解释表面偏析。将进行基于爱德华兹自洽场理论的理论计算，以将这些实验观察置于合理的理论基础上。除了探索这种“构象不对称”聚合物共混物和具有小混合热的共聚物（例如，聚烯烃），将进行计算以研究“结构上不对称”聚合物共混物（例如由相同化学重复单元组成的线性和星星聚合物的混合物）中的界面热力学和润湿行为。表面富集的检查也计划熔融聚合物共混物，包含星嵌段共聚物，并打破构象和建筑对称性可能会竞争。这些研究的目的，如果开发的结构-性能关系，将有利于合理设计的聚合物界面工程应用。提出的理论工作将与目前正在进行的平行实验工作相协调。对聚合物表面的性质进行理论研究。特别是，为什么某些类型的聚合物倾向于迁移到聚合物混合物和固体的表面的问题将被探索。虽然具有根本利益，但这个问题也具有高度的技术利益，因为它影响了我们涂覆和油漆塑料的能力。***

9505599 Fredrickson With the advent of powerful new surface characterization techniques, a number of experimental groups have reported on the surface segregation and wetting behavior of multicomponent polymer blends, as well as block and random copolymers. Surface energy differences between components are generally assumed to be responsible for producing the inhomogeneous composition profiles in such systems. Very recent experiments on model polyolefin blends and copolymers, however, have shown that a strong correlation exists between interfacial thermodynamics and the difference in conformational properties (i.e., backbone flexibilities) of the components, leading to an alternative entropic explanation for surface segregation. Theoretical calculations based on the self-consistent field theory of Edwards will be performed to place these experimental observations on a sound theoretical footing. Besides exploring surface enrichment in such "conformationally asymmetric" polymer blends and copolymers with small heats of mixing (e.g., polyolefins), calculations will be performed to investigate interfacial thermodynamics and wetting behavior in blends of "architecturally asymmetric" polymers, such as mixtures of linear and star polymers composed of the same chemical repeat unit. An examination of surface enrichment is also planned for molten polymer blends that contain star-block copolymers, and for which broken conformational and architectural symmetries may compete. The objective of these studies if to develop structure-property relations that will facilitate the rational design of polymer interfaces for engineering applications. The theoretical work proposed will be coordinated with parallel experimental efforts currently underway. %%% Theoretical research will be conducted on the properties of polymer surfaces. In particular, the question of why certain types of polymers tend to migrate to the surfaces of polymer mixtures and solids will be explored. While having fundamental interest, this problem is also of high technological interest since it impacts our ability to coat and paint plastics. ***