Stratification and phase separation in block copolymer coatings

Abstract

Stratification, i.e. spontaneous formation of separate layers from a liquid coating containing inherently incompatible resinous components, provides a means of improving the adhesion of coatings. For mixtures of conventional homogeneous resins, surface and interface tensions are considered to be the driving forces for self-stratification, leading to films with separation patterns somewhere between purely spinodal decomposition textures and neatly separated A/B double layers. Inherently domain-forming block copolymers mixed with partly compatible resins give various different separation patterns ranging from ABA-sandwich structures to physically interpenetrating networks of co-continuous phases with homogeneous layers — sometimes monomolecular ones — at film surfaces. Besides tailoring adhesion to difficult substrates, block copolymer binders offer chances to achieve new interesting mechanical property profiles as required, e.g. for coatings for plastics or for stone chip-resistant surfacers useful in the automotive industry. The temperature-dependence of mechanical properties is significantly reduced in comparison with conventional homogeneous coating binders.