A stability analysis of polymerization fronts.

摘要

Frontal Polymerization (FP) is a process of converting monomer into polymer via a localized zone that propagates through the monomer. It bears a strong resemblance to self-propagating high-temperature synthesis (SHS), which uses combustion waves to synthesize desired inorganic materials. The reaction front propagates through the coupling of thermal diffusion and the Arrhenius reaction kinetics of the exothermic polymerization process. This thesis utilizes a moving free-boundary model to describe free-radical FP. The focus of attention here is the self-sustaining wave which travels through the reaction vessel as polymer molecules are being formed. Numerical and analytical techniques are used to determine one-dimensional traveling waves, and stability analysis (linear and weakly nonlinear) of the reaction front is performed. It is then possible to suggest ways to curb instabilities in the propagating reaction front. After our initial analysis, we account for autoacceleration and determine its effect on frontal stability. In an effort to facilitate the propagation of weakly exothermic fronts, we consider a one-dimensional polymerization wave in a sandwich-type two-layer setting. First one layer is reactive while the other is considered to be inert. Heat exchange between layers is possible, and the effect this has on frontal stability is investigated. Next, we allow both layers to be reactive, thus further enhancing inter-layer heat exchange. We comment on the effect that the second reactive layer has on the basic state of the system. Finally, two future research directions are presented in detail. One of our goals is to determine how the propagating front is affected by bulk polymerization at the far end of the reaction vessel. This is an important aspect to be studied in greater depth and incorporated into existing FP models, since bulk reactions can influence the speed and long-term stability of the reaction front. We end with a theoretical discussion for the manufacture of polymer-dispersed liquid crystal films via FP.