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Wednesday, May 17, 2017 at 4 p.m.
Johnson Hall Auditorium 102 [Directions]
It is widely recognized that the mechanical properties of particle-filled polymeric composites depend critically on the strength of adhesion between the particle surfaces and the matrix polymer. What is less widely agreed upon is the prospect for quantitatively predicting or ranking practical adhesion in terms of the energetics of the adhesive and adherend surfaces and the presence of possible acid-base interactions across the interface. This talk deals with these issues.
Silica particle surfaces are systematically modified using silane coupling agents, and their surface energy and acid- base properties are determined using inverse gas chromatography. Adhesion properties are determined directly by a method in which a single spherical filler particle is embedded in the matrix. The single particle composite specimen is subjected to uni-axial tension until interfacial failure occurs at one of the poles, detected both optically and acoustically, and yielding the stress at failure, without edge effects.
From such measurements, interfacial strengths associated with the different coupling agents are determined analytically. They are found to correlate on the one hand with the yield stress for highly filled composites and on the other hand with a new thermodynamic parameter computed using UNIFAC (a group contribution method) or COSMO-SAC (a DFT method) for the interaction between the polymer and the silane coupling agent. The database developed thus far suggests the prospect of ab initio prediction of the relative effectiveness of coupling agents for promoting adhesion.
John C. Berg is Rehnberg Professor of Chemical Engineering at the University of Washington. He is author or co-author of 215 refereed articles and book chapters in a wide variety of problems in the area of interfacial and colloid science. His bestselling 2010 textbook, An Introduction to Interfaces and Colloids: The Bridge to Nanoscience, has been adopted at more than 50 colleges and universities worldwide.