Department of Chemical Engineering University of Washington - Seattle
"Can We Use Thermodynamics to Predict Adhesion?"
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. The present report 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 new 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) 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.
"The Magic of Interfaces and Colloids: The Bridge of Nanoscience"
The importance of Interfacial and Colloid Science across the spectrum from industrial manufacturing to energy development to biomedical research to everyday activities from cooking to cleaning is beyond dispute, but the subject is found in relatively few curricula in science and engineering in our universities. A shift is underway, however, as more elective courses in it are emerging in Chemical Engineering programs. At the University of Washington, it has recently become a required course, where it is recognized as vital not only in its own right, but as a gateway topic to nanoscience and nanotechnology. This presentation is an introductory overview of the subject and where it fits into a modern Chemical Engineering curriculum.