Mechanism of Enhanced Adhesion Strength of Multi-layer Films via Multi-block Copolymer Compatibilizers: Coarse-Grained Simulation Study

Multi-layer films of immiscible polymers, such as poly(ethylene terephthalate) and poly(ethylene), have been realized by introducing multi-block copolymer (MBCP) compatibilizers leading to the enhancement of interfacial adhesion strength. However, the mechanism of the enhanced adhesion, while several candidates have been proposed, remains elusive. Here, we present a coarse-grained simulation study to investigate the mechanism of the enhanced adhesion due to the MBCP compatibilizers. Starting from a binary polymer blend of A (repulsive) and B (attractive) homopolymers mixed with MBCPs composed of A and B, we first form a bilayer where MBCPs are localized at the A-B interface. Then, the adhesion strength of the bilayer is quantified by applying uniaxial elongation to the bilayer and obtaining a stress-strain curve. We report how block length, number of blocks, concentration of MBCPs, etc. affect the adhesion strength and discuss the importance of having entanglements between the MBCP blocks and the homopolymers in each layer. This study, if the miscibility of MBCPs is simultaneously optimized, provides a way to design optimal multi-component materials with satisfactory adhesion strength from arbitrary combinations of raw materials.