Theoretical Modeling of the Phase Separation Dynamics in Blends of Reactive Monomers

Abstract

AbstractSummary: Experimental observations of the dynamics of phase behavior for blends of reactive constituents, i.e. diglycidyl ether of bisphenol A (DGEBA), curing agent methylene dianiline (MDA), and a reactive liquid rubber (R45EPI), have been theoretically modeled by coupling system thermodynamics governed by a summation of the free energies of mixing and network elasticity with reaction kinetics and diffusion equations. Snap‐shots of the temporal evolution of ternary phase diagrams have been established based on the self‐condensation reactions of DGEBA‐MDA and R45EPI as well as a cross‐reaction between the two constituents forming a copolymer. Numerical solution of the proposed mean‐field model provides good qualitative agreement with experimental results, namely, the observance of phase separation followed by a phase dissolution and subsequent secondary segregation in a 50/25.4/50 DGEBA/MDA/R45EPI mixture, as well as a single gradual phase separation in a 70/25.4/30 mixture. The phase separation dynamics are explained by a competition between the growth in molecular weights of the reactive species rendering the systems towards instability, and the formation of copolymer acting to compatibilize the mixtures.Theoretical phase diagram for a DGEBA/MDA/R45EPI system.magnified imageTheoretical phase diagram for a DGEBA/MDA/R45EPI system.