Crystallization-Programmed Isotactic Polystyrene Towards Membrane Architecture: Quantitative Optical-Thermal Kinetics

Crystallization can be exploited as an architecture-forming step for polymer membranes because it builds a load-bearing semicrystalline scaffold while simultaneously defining amorphous regions that later become transport pathways. Herein, we quantify how thermal history programs isotactic polystyrene (iPS) crystallization and translate the resulting microstructures into membrane-relevant design rules. Lux-calibrated digitally extracted pixel intensity (DPI) from polarized optical microscopy provides a quantitative, spatially resolved crystallinity proxy; benchmarking against differential scanning calorimetry confirms that the DPI proxy exhibits the same onset, peak, and completion signatures under matched temperature programs. The DPI-DSC agreement yielded R² = 0.98 under matched programs. We compared crystallization initiated from molten and glassy states across a wide range of melt pretreatments and crystallization temperatures. Molten-state pathways display pronounced melt-memory behavior: modest changes in melt pretreatment shift induction time and half-time and drive textures from dense, fine spherulitic fields to sparse, coarser morphologies. In contrast, glassy-state crystallization largely suppresses melt history, yielding overlapping sigmoidal crystallinity curves and stable kinetic parameters consistent with relaxation-mediated nucleation. Avrami analyses indicate three-dimensional growth in both routes but highlight the strong melt-history sensitivity of apparent rate constants in the molten state. The crystallization rate and half-life show bell-shaped temperature dependence. Finally, saturated nucleation density correlates with the melting response, providing a practical link between kinetic observables and morphology. The processing-morphology map provides membrane-relevant design rules by linking thermal history to nucleation density and scaffold texture, which are expected to influence transport and mechanical stability in downstream membrane fabrication. In this study, "membrane architecture" is used in a pre-fabrication sense to denote the crystallization-programmed semicrystalline scaffold expected to govern subsequent pore-generation behavior and mechanical stability. Accordingly, the present work establishes a quantitative process-structure map for iPS scaffold design.