Confined Polymer Crystallization in Vapor-Deposited PE/PMMA Blend Films*

Polymer blends are widely applied in technologies because they can join features from individual components to optimize performance. However, for thin films comprising immiscible polymers, it is challenging to precisely control the film structure because of the spontaneous phase separation, which can influence the resulting properties in an undesirable way. In this work, we utilize a vapor deposition technique termed matrix-assisted pulsed laser evaporation (MAPLE) to process thin films of PE/PMMA and illustrate that the technique can effectively control the size of phase separation. During MAPLE, thin films are formed atop a temperature-controlled substrate by the addition of separate nanoscale polymer droplets at an ultra-slow rate, thereby confining the phase separation within a much smaller scale relative to films processed via other means. Employing a fast scanning calorimeter, we demonstrate the ability to shift the crystallization temperatures of PE by ~20°C as a result of confinement and temperature during deposition. We also show the preservation of film structures beyond melting.