Understanding how asymmetric confinement modulates the self-assembly of block copolymers (BCPs) is crucial for expanding accessible morphologies beyond equilibrium phase boundaries. Here, we demonstrate that rigid conical confinement, with a gradient design providing varying degrees of confinement in a single experiment, can modulate the phase behavior of lamellae-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS). Combined results of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) reveal marked leftward shifts of phase boundaries, yielding inverted hexagonally packed phases (HEX′) and double-gyroid morphologies from lamella-forming PS-b-PDMS. Under rapid solvent evaporation, a rarely observed tetragonally packed cylindrical (TPC) phase, typically inaccessible in coil–coil BCPs, emerges and remains thermally stable. Using quartz crystal microbalance with dissipation (QCM-D), we quantitatively analyze the evolution of the effective PS volume fraction (fPSeff) in a rigid confined environment. The results indicate that fPSeff decreases because of confinement-enhanced interfacial adsorption and restricted chain conformations of PS during solvent evaporation, leading to systematic shifts in the accessible morphologies relative to solution-casting processing. These findings establish a physical framework in which geometric asymmetry and interfacial adsorption synergistically modulate morphologies, providing a general strategy for controlling the phase behaviors of BCPs without the need to alter molecular composition.
Zhan et al. (Thu,) studied this question.