Photo-induced Block Copolymer Transitions in Ionic Liquids

Photo-stimuli are widely used to induce changes in polymer systems, from crosslinking to curing. However, the ability to influence the phase behavior of a block copolymer with light remains underexplored. Our group has previously shown that the order-disorder transition (OD) of poly(methyl methacrylate)-b-poly(benzyl methacrylate) in imidazolium-based ionic liquids, a lower critical ordering transition behavior system, can be controlled with light by incorporating an azobenzene-based monomer into the poly(benzyl methacrylate) block. Our studies also demonstrated the ability to tune the OD by changing the solvent quality through the alkyl chain length on the ionic liquid cation. To explore this behavior further, we use small-angle X-ray scattering to identify the ordered states formed by the system and UV-irradiated small-amplitude oscillatory shear rheology (UV-SAOS) to observe the photo-response. The UV-SAOS involves a lower plate attachment to our rheometer where a light source can be guided into a channel and reflected on a mirror up through a quartz lower plate onto the sample. This allows for the sample to be irradiated in operando. We will discuss how the phase behavior of this system is influenced by varying the ratio of responsive to inert block in the polymer, as well as the relative azobenzene monomer content in the responsive block.

 

Funding: NSF Polymers Program, DMR-2103630