Self-Assembly of Ultrahigh Molecular Weight Block Copolymers under Dissipative Solvent Vapor Annealing

Ultrahigh molecular weight block copolymer (UHMW BCP) (M_n > 500 kg/mol) is dictated by desire to create the material with the larger features size and interdomain spacing above 150 nm to gain the flexibility in further tuning the block architecture across the film. High chain entanglement of UHMW BCP usually results in extremely slow ordering kinetics. Solvent vapor annealing has been used to facilitate the polymer chain mobility by selective solvent swelling and lowering the effective value of T_g. In addition to conventional self-assembly to reach the thermodynamic equilibrium, dissipative self-assembly (DSA) is the out-of-equilibrium process driven by input energy dissipation. However, DSA hasn't been applied to BCP due to temporal control over assembled structures under energy unfavorable conditions. Here, benefiting from the slow molecular dynamics and large domain size from UHMW BCP, the system can be pushed out of equilibrium in a controllable manner. We use Polystyrene-b-poly(2-vinylpyridine) to study how the oscillating manner of the mixture solvent vapors will prevent the system from reaching equilibrium state. The dense packed and ordered micelle structure can be achieved only by dissipating solvent vapor annealing, and the structure varies with the thickness of film.