Viscoelasticity of lamellae-forming block copolymers

NICOLÁS A GARCÍA; BARRAT, JEAN-LOUIS

Buenos Aires

Conferencia; StatPhys 27; 2019

Unraveling the underlying physics in the viscoelastic behavior of polymers is of fundamental interest but also is relevant to consider their technological applications. It is well-known that the mechanical properties of polymers in melts and concentrated solutions depend fundamentally on the molecular weight of the chains. Indeed, the natural inability of the chains to cross each other comes into play when the chain-length increases inducing mobility constraints for them; thus the so-called entanglements appear. At present, we know the entanglements are a universal aspect of the polymer physics which happen in any flexible polymer if the chain is sufficiently long and the concentration is high enough.Entanglements in homogenous systems in bulk conditions have been extensively studied through simulations and experiments, and some elegant theories provide the conceptual frameworks to interpret their behavior. Furthermore, similar studies were recently reported on inhomogeneous systems like confined environments: thin films, nanocylinders, etc. However little is known about those topological constraints on heterogeneous systems and multicomponent polymers like block copolymers (BCPs), a fascinating system which in the proper conditions of temperature and composition tends to self-assembly in periodic nanopatterns of high technological interest.In this work, we investigate the viscoelastic properties of BCPs when segregating in a lamellar morphology. We have performed a thorough analysis to characterize their statics and dynamics.We found the entanglements are not distributed homogeneously in the space but instead adopt a to the underlying pattern as a direct consequence of the periodic location of the segregated domains. Moreover, the interface separating nearby domains induces a surface effect decreasing locally the density of entanglement. This effect seems to depend on the segregation regime being more extended in space in the regime of strong segregation (sharp interfaces).Regarding the dynamics, we found the entanglements play a crucial role in the kinetic pathway to the equilibrium of the self-assembly process and seem to favor the stability of the topological defects of the pattern, an undesired effect when their technological applications are considered.