Circumventing Macroscopic Phase Separation in Immiscible Polymer Mixtures by Bottom-up Deposition

Achieving intimate mixing in immiscible polymer blend thin films is of paramount importance for maximizing their performance in numerous applications such as membranes, electronics, and energy devices. Here, we introduce a promising approach to confine and stabilize phase separation in an immiscible polymer mixture using a bottom-up technique termed matrix-assisted pulsed laser evaporation (MAPLE). Using polyethylene/poly(methyl methacrylate) as a model blend system, we demonstrate that the mechanism of thin-film growth by MAPLE, which geometrically confines a polymer into nanometer- to micrometer-size clusters during film formation, can act to kinetically trap strongly immiscible polymer mixtures, which in turn limits the extent of phase separation of the resulting film without the need for compatibilizers. Due to the unique morphology, the films exhibit distinct thermal properties in comparison to macroscopically phase-separated films. Our results present a promising technique for polymer thin-film fabrication and blending, which could inspire the design of thin films with exceptionally integrated properties.