Order-to-Disorder Transition of Cylinder-Forming Block Copolymer Films Confined within Neutral Interfaces

Abstract

We present the phase behavior of cylinder-forming block copolymer (BCP) films confined within neutral interfaces through theory and experiment. The Langevin field-theoretic simulation (L-FTS) is utilized to account for the compositional fluctuation effect on the order-to-disorder transition (ODT), and the ultraviolet divergence in the L-FTS result is eliminated by renormalization of the Flory-Huggins parameter chi, allowing accurate comparison of thickness-dependent (chi N)(ODT), where N is the polymerization index. The L-FTS is accelerated by utilizing a deep learning method, and we managed to achieve a 50-60% reduction in simulation time. The L-FTS results show that (chi N)(O)(DT) decreases as the film thickness decreases at a very large value of the invariant polymerization index ( N) over bar, and BCPs undergo a phase transition from disordered to cylindrical phases through a spherical phase as predicted by the self-consistent field theory calculation. By performing the L-FTS at experimentally relevant low (N) over bar, we show that the BCPs undergo a direct transition from disordered to cylindrical phases, and the (chi N)(O)(DT) value of cylinder-forming BCPs confined within neutral interfaces increases as the film thickness decreases. To verify and complement the theoretical results, we investigate the ODT temperature (T-ODT) of cylinder-forming polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) films supported on a neutral mat of P(S-r-2VP) random copolymers using grazing-incidence small-angle X-ray scattering. Our film experiments with low-(N) over bar PS-b-P2VP confirm the direct transition from disordered to cylindrical phases and the decrease in T-ODT with decreasing thickness below the onset thickness above which the T-ODT levels off.