Effect of the Backbone Kuhn Length and Flory Parameter on Microphase Separation in Brush Copolymer

Brush copolymers with immiscible backbones and side chains microphase separate with increasing value of the Flory interaction parameter and decreasing grafting density of the side chains. We use coarse-grained molecular dynamics simulations to study how backbone rigidity (Kuhn length), side chain grafting density and strength of interactions between side chains and backbones influence order-disorder transition in a melt.  Simulations show that immiscible backbones and side chains microphase separate into: (i) “hairy” filaments, arranged into gyroid-like network of backbones coated by stretched side chains, and (ii) randomly oriented lamellae whose interfaces are covered by brushes of side chains. With increasing stiffness, backbones align along axes of the hairy filaments or adopt a preferred orientation parallel to lamellar interfaces. Such spatial organization of the backbones is dictated by optimization of the backbone bending energy and requirement of the expulsion of the side chain grafting points to the lamellar interface. Analysis of the structure factor S(q) quantifies how the copolymer brush architecture and backbone Kuhn length control location and sharpness of the observed peaks.