Macromolecular Spreading

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

TECHNICAL SUMMARY: The macroscopic behavior of polymer fluids during spreading on solid surfaces is well understood, yet our understanding of the molecular mechanism of spreading remains incomplete and controversial. This lack of microscopic knowledge is now an urgent problem limiting developments in various microtechnologies, whose characteristic time and length scales are approaching those of individual molecules. The goal of this program is to achieve a fundamental understanding of the wetting-induced changes in the dynamics, conformation, and chemical structure of surface-confined macromolecules. Specifically, the funded research will focus on (i) the flow-induced molecular diffusion with direct implications to ordering, mixing, and chemical reactions of macromolecules in flow; (ii) the development of molecular sensors for quantitative measurements of the pressure gradient and friction coefficient, which will lead to understanding of the lubrication effect of surface-condensed vapors on the spreading mechanism and flow rate; and finally (iii) the wetting-induced degradation of highly branched macromolecules. The final focus opens an entirely new avenue in the field of reactivity and functioning of adsorbed macromolecules. Preliminary, the Sheiko group has achieved a breakthrough in experimental studies of the flow structure on the molecular scale. Through molecular visualization, it was demonstrated that flowing macromolecules actively responded to variations in the interfacial properties through changes in both their secondary and primary structures. The previous work set the foundation for the development of a new methodology that will open a vast array of opportunities to both study and control the flow in thin films on the scale below 100 nm. NON-TECHNICAL SUMMARY: The flow properties of molecularly thin polymer films impact coatings, composites, microfluidics, and lubrication. This program will advance fundamental understanding of the conformation and dynamics of surface-confined polymer chains and lead to the development of new technologies for controlling flow on molecular length scales. This work will also lead to elucidation of the effect of the polymer architecture on the wetting kinetics. The program will provide interdisciplinary research training for graduate and undergraduate students, since it combines fine polymer chemistry and advanced experimental techniques. One of the strategic goals is to bring molecular visualization to university and high-school classrooms where the ability to see molecules would be invaluable for the teaching of reaction mechanisms and conformation of polymer molecules. Molecular visualization will be added to polymer courses as new laboratory module and also used as a demonstration tool during regular scientific seminars at the local high schools.