Isotropic Lifshitz Behavior in Block Copolymer-Homopolymer Blends

Abstract

A series of mixtures composed of a symmetric $A\ensuremath{-}B$ diblock copolymer and a symmetric blend of $A$ and $B$ homopolymers was investigated by small-angle neutron scattering. Mean-field theory predicts that a line of lamellar-disorder transitions with wave-vector instability ${q}^{*}>0$ will meet a line of critical points with ${q}^{*}=0$ in the three-component mixture at an isotropic Lifshitz point. Mean-field Lifshitz behavior ($\ensuremath{\gamma}=1$ and $\ensuremath{\nu}=\frac{1}{4}$) was observed in the disordered state at the anticipated composition to within 1 K of the phase transition.