Manoj K. Chaudhury

Professor of Chemical Engineering
Franklin J. Howes Jr. Distinguished Professor


Ph.D. State University of New York at Buffalo, 1984
M.S. State University of New York at Buffalo, 1980
B.S. Calcutta University, 1976

Contact Information:
phone: (610) 758-4471
personal webpage: http://www.Lehigh.EDU/~mkc4/
e-mail: mkc4@lehigh.edu

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Research Interests.
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Surface Modification of Organic and Inorganic Materials

Novel methods of modifying the surfaces of organic and inorganic materials are being developed to enhance their performance in such areas as adhesion, friction, wetting, and biocompatibility, without affecting their otherwise desirable bulk material properties. The technology of self-assembled organic monolayers has been used to modify the surfaces of a whole range of polymers, metals, and ceramics. Long-chain polymers have also been grafted onto inorganic surfaces to modulate their adhesive and tribological properties. Other approaches include graft polymerization and derivitization by electron beam. The techniques used to characterize the chemically modified surfaces include X-ray photoelectron spectroscopy, near edge X-ray absorption fine structure spectroscopy, ellipsometry, infrared spectroscopy, and wettability measurements.

Non-Equilibrium Processes at Interfaces

A method has been formulated for estimating the interaction energies between elastomeric surfaces in air and under liquid media that provides information about adhesion at the microscopic level. The major finding is that interactions between solid materials generally have a strong hysteritc component, indicating that the solid surfaces have no unique equilibrium energy states. The possible factors contributing to adhesion hysteresis are (1) interdigitation of the surface functional groups, (2) dipolar transitions at the surface, (3) pinning due to heterogeneities and defects of surface structure, and (4) charge exchange across the interface. We are seeking a molecular-level understanding of the hysteresis phenomena that occur at polymer surfaces, and a unified picture of its roles in such interfacial processes as adhesion, friction, wetting, and adsorption of macromolecules.

Adhesion of Cross-linked Networks

Adhesive fracture strength of cross-linked materials is generally attributed to two major mechanisms that absorb and dissipate energy. These contributions stem from the extension and breaking of polymer chains, chain deformation, and chain pulling. A simple experimental protocol is being developed to investigate some of these factors in a controllable fashion. Methods have been established to graft polydimethylsiloxanes of varying chain lengths onto a rigid support previously coated with self-assembled organic monolayer. Only one end of the chain end is bonded to the surface; the other end is free. By varying the concentration of the reactive groups of the monolayer surface, the density of the grafted chains can be controlled easily. These model surfaces, coupled with the ability to continuously vary the crosslinking density of rubbery polymers, form the basis of an ideal experimental system for examining some of the simpler concepts of adhesive fracture resistance in rubbery networks.

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