Block Copolymer Response to Photothermal Stress Fields
Majewski, P.W.; Yager, K.G. "Block Copolymer Response to Photothermal Stress Fields" Macromolecules 2015
We use photo-thermal methods to generate extreme shear fields, and study the response of block-copolymer materials to these conditions. Photo-thermal shearing allows soft self-assembled morphologies to be rapidly aligned, with response depending on material properties.
Block copolymer materials can be aligned using shear forces; in order to fully exploit this phenomenon for controlling nanoscale order, the coupling between applied forces and molecular properties must be elucidated. We use a photothermal method to generate extreme and controllable thermal and stress fields in thin films of cylinder-forming block copolymers. By studying morphological ordering as a function of time, shear rate, polymer material, molecular weight, and film thickness, we elucidate the critical parameters with respect to efficient ordering. We find that ordering efficiency depends weakly on the block copolymer interaction parameter and strongly on the difference in mechanical response of the two phases. Morphologies can be aligned only when the inverse shear rate is smaller than the material’s relaxation time. Overall, photothermal shear alignment provides an efficient means of ordering and aligning nanoscale morphologies over macroscopic areas, using a surprisingly short (subsecond) shear pulse.