Characterization of vertically stratified films produced from binary polymer-colloid mixtures

This study investigates the use of stratification, a single-step evaporative drying technique, to create vertically structured multi-component polymer and colloid films. Films containing poly(acrylic acid) (PAA) and polystyrene (PS) colloids were analyzed using microbeam Small-Angle X-ray Scattering (SAXS) and Atomic Force Microscopy (AFM) under varied compositions and drying conditions. We aim to clarify the influence of evaporation rates and colloid sizes on stratification dynamics. Our findings show that under atmospheric drying conditions, particle-on-top stratification was observed, consistent with the Peclet number theory. Conversely, increased evaporation rates in medium evaporation systems led to non-stratified configurations for certain mixtures. Fast evaporation drying at elevated temperatures induced polymer-on-top stratification, aligning with theoretical predictions. AFM images supported these findings, with slow evaporation conditions revealing particle-on-top stratification and fast evaporation conditions validating polymer-on-top stratification. This work enhances our understanding of polymer-colloidal film stratification, emphasizing the significance of drying conditions, Peclet numbers, and colloid size. Overall, our study proposes a more efficient method for creating vertically structured films with implications for various industries.