Kinetics of Domain Alignment in Block Polymer Thin Films during Solvent Vapor Annealing with Soft Shear: An in Situ Small-Angle Neutron Scattering Investigation

We employed small-angle neutron scattering (SANS) to identify the kinetic pathways between disordered and ordered states in block polymer (BP) thin films subjected to solvent vapor annealing with soft shear (SVA-SS), which enabled the optimization of large-scale nanostructure ordering and alignment. The judicious incorporation of deuteration in poly(deuterated styrene-b-isoprene-b-deuterated styrene) (dSIdS) films (approximate to 200 nm thick) provided sufficient contrast in the SANS experiments to overcome the diffuse scattering contribution from thicker (nondeuterated) polydimethylsiloxane (PDMS) pads (approximate to 500 mu m thick) and permit the in situ tracking of BP nanostructure responses to swelling, deswelling, and shear forces. We determined that as the dSIdS and PDMS swelled during SVA-SS, the lateral expansion of the PDMS across the pinned film induced a shear force that promoted chain mixing and nanostructure disordering in our solvent swollen systems. As solvent was removed from the films (deswelling), smaller grains began to form that had lower energetic barriers to alignment in the direction of the drying front(s), which facilitated nanostructure alignment. Changing SVA-SS parameters such as swelling ratio, PDMS elasticity, and deswell rate altered the ordering kinetics and affected domain directionality Over a length scale that was readily captured through SANS studies. By exploiting SVA-SS parameters that create large and controllable shear forces, we also developed a robust and "hands-off" approach to direct BP thin film self-assembly using gradient thickness PDMS pads in SVA-SS. This proposed technique can be applied to quickly and reliably generate cost-effective microscopic patterns over macroscopic areas for both nanotechnology research and industrial applications.