The Studies of Polymer Adhesion Using Segmental Dynamics Model

Abstract

157 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1997.Polymer adhesives play a very important role in many applications. However, because it is very hard to observe an amorphous polymer at the molecular level, there are many questions about adhesion and failure mechanisms. Several computer simulation techniques have been of great success in describing the dynamics of generic polymers, but are unable to reliably simulate the mechanical deformation of polymer adhesives. Therefore, it was necessary to develop improved coarse-grained potentials for a method we call Segmental Dynamics. Segmental Dynamics employs extensive atomistic Monte Carlo simulations to develop the interaction potentials custom-made for a specific polymer. This makes it possible to study the dynamics of larger scale polymer systems, which is not possible with conventional molecular dynamics techniques. The method was first applied to bulk polybutadiene, and the model was found to describe the density, bulk modulus, and cohesive energy fairly well. The model was further verified by investigating the structure and dynamics of bulk polybutadiene. Also, the effects of high density and high pressure on the dynamic properties of bulk polymers were investigated. Both of these effects significantly increase internal friction coefficients and thus slow down the diffusion of the polymer. Then, the model was applied to dynamic mechanical simulations of an adhesive film between two surfaces at a constant temperature. The equilibrated structure of the polymer revealed that the loop and tail structures are randomly distributed, but are very sensitive to the anchor group density. A series of simulated tensile tests were carried out with varying anchor group densities, and the effects of the bond strength of anchor groups, strain rate, chain length, plasticizers, and surface roughness were identified.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD