Optical Alignment of Si-Containing Nanodomains Formed by Photoresponsive Amorphous Block Copolymer Thin Films

A series of amorphous block copolymers (BCPs), consisting of a low-glass-transition polydimethylsiloxane (PDMS) block associated with a photoresponsive azobenzene-containing poly(disperse red 1 methacrylate-co-alkyl methacrylate) (P(DR1MA-co-RMA)) block, were prepared from a PDMS macro-chain transfer agent used for the reversible addition–fragmentation chain-transfer (RAFT) copolymerization of binary mixtures of methacrylate monomers of various compositions. The resulting BCPs containing up to 40 wt % of azo dye exhibited low dispersity demonstrating a good control of the RAFT polymerization through the copolymerization of the DR1MA and RMA units. Long-range-ordered in-plane PDMS cylinders were produced by exposing the (as-cast) disordered BCP thin films to a p-polarized laser beam, to orthogonally align the azo groups with the polarization direction, prior to promoting the microphase separation of the BCP domains with a solvent vapor annealing treatment. Conversely, the photoinduced alignment of the azo chromophores was not effective within microphase-separated BCP thin films since randomly oriented PDMS features were observed after exposure to a p-polarized laser light.

M. C. Spiridon, N. Demazy, C. Brochon, E. Cloutet, G. Hadziioannou, K. Aissou, G. Fleury

Macromolecules 53, 1, 68-77, https://doi.org/10.1021/acs.macromol.9b01551 2020