Component compatibility study of poly(dimethyl siloxane) with poly(vinyl acetate) of varying hydrolysis content: An atomistic and mesoscale simulation approach

Molecular simulations are very promising computational methods to understand miscibility of polymers, surface behavior and bulk properties of materials. In this investigation, such useful computations have been carried out on blends of hydrophobic poly(dimethyl siloxane) (PDMS) with commercially available hydrolyzed grades (0%, 86% and 100% hydrolysis) of poly(vinyl acetate) (PVAc) present in varying weight fractions. The material properties like Flory-Huggins interaction parameter (χ), blend compatibility and thermal transitions have been estimated by atomistic molecular dynamics (MD). The glass transition temperature (Tg) has been estimated for pristine polymers and their blend systems as well, which are found in line with previously reported values. However, some blend systems displayed occurrences of multiple Tg's, thereby, signifying phase separation. χ values have been estimated from atomistic simulations and compared with critical χC. Among different potential energy components, torsional energy plotted against a range of temperature (~90-350 K) showed distinct inflection points near Tg. In addition, morphology has also been predicted using Dissipative Particle Dynamics (DPD) and Mesoscopic dynamics (Mesodyn) simulations in order to visualize phase segregation and results found in accord with χ and Tg studies. Interestingly, while the atomistic MD and mesoscale simulations of short-chain systems (Mw ~2000) predicted limited miscibility, the mesoscale simulations of large chain lengths (Mw ~1,00,000) depict complete immiscibility at all blend contents and all hydrolyzed PVAc grades. The blend compatibility study using atomistic and mesoscale simulations indicates that incompatibility increases with increasing degree of hydrolysis, chain length and PVAc content. Further, simulations help screen 20 wt% PVAc (0% hydrolysis and 86% hydrolysis) or 10 wt% of PVOH (100% hydrolysis) in PDMS as an optimal formulation with improved miscibility characteristics.