Stimuli-responsive phase behavior of block copolymers in ionic liquids

Block copolymers microphase separate into well-defined ordered morphologies as a function of temperature and composition. However, not all applications are amenable to changes in temperature or composition, but still require transitions between disorder and order, or between different ordered symmetries. We explore the light-mediated phase behavior of a diblock copolymer, poly(methyl methacrylate)-b-poly(benzyl methacrylate-s-4-phenylazophenyl methacrylate), in a selective ionic liquid solvent, 1-alkyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide. By adjusting the length of the alkyl chain on the imidazolium group, we can control the phase transition temperatures (order-disorder and order-order transitions). In this system, the solubility of the 4-phenylazophenyl methacrylate-containing block in the ionic liquid is altered by irradiation with UV light. The phase behavior is monitored by small amplitude oscillatory shear rheology under either UV or visible light, and the ordered phases identified by small angle X-ray scattering. Understanding the phase behavior of this model system allows us to work towards inducing morphology changes in a contactless manner.