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Polymer Science and Engineering: The Shifting Research Frontiers
Polymer Surfaces and Thin Films
A number of surface properties of polymers, such as friction, wear, lubrication, adhesion, and sorption of surface species, have been investigated for many years because of their technological importance. But these studies have tended to be macroscopic and empirical, and thus little is known at the molecular level. It is observed that surface enrichment occurs where species preferentially concentrate at the surface according to composition and molecular weight. Surface segregation and phase separations near surfaces are not well understood. Nor is much known about the interactions between polymer surfaces and other materials such as liquid crystals, for example, in flat panel displays. Experimental methods to study the structures and properties of polymers on the 10- to 100-Å thickness scales are limited. Theoretical and computational efforts are critically needed to fill in details from the limited available experiments, which are often difficult and costly to perform.
Biopolymers are another important class among polymeric states of matter. Biomolecules adopt an extremely wide variety of structures, spanning a large range of different types of organization and hierarchical complexity. Biology has control over specific monomer sequences, a power that is not yet available in synthetic polymer chemistry. It is the sequences, for example of proteins, RNA, and DNA, that control molecular architectures, and they do so with a high degree of precision. Force-field simulations for polymers were mainly developed first in the biomolecules area, and they continue to be of major importance in understanding biomolecule properties. More synergy is desirable between the polymer and biopolymer communities, because many of the needs and problems for theories and simulations are the same. Major needs in this area are for (1) theories and simulations that can couple and bridge a wide range of time and spatial scales and (2) better understanding of the complex interactions, such as electrostatic, hydrophobic, and hydrogen bond forces, that are important for biomolecules and other polymers in water.
Dynamics and Properties
Local Motions in Polymers
Localized motions in polymers include the same vibrational and torsional movements that are characteristic of motions in small molecules. However, the connectivity of a polymer chain introduces additional scales of "local motion," which can range from side-group rotations to cooperative movements involving segment sizes with tens of repeat units. It is these localized segmental motions