Hierarchical surface structures are abundant in nature, from beetle carapace to plant leaves. This multi-level patterning enhances the surface, resulting in unique wettability, adhesion, and self-cleaning behavior. The interactions between hierarchically structured surfaces and water continue to inspire researchers and motivate new strategies to mimic these designs to harness their extraordinary performance. Here, photoinduced phase separation (PIPS) is utilized as a single-step process to generate hierarchical topographical features on polymer surfaces. PIPS holds promise as it is capable of leveraging both classic surface wrinkling phenomenon as well as associated patterning from phase separation to achieve structures on multiple scales. This work investigates the in situ phase separation and surface roughening during polymerization of resins consisting of acrylonitrile, 1,6-hexanediol diacrylate, and poly(methyl methacrylate). Real-time kinetic analyses were conducted in non-phase separating controls to determine the kinetic rate constants associated with propagation and termination events. This provided information regarding the evolution of diffusional constraints during polymerization and thus the assumed limitations to phase diffusion with simultaneously occurring phase separation. Most notably, a significant decrease (several orders of magnitude) in the termination kinetic rate constant was observed from data collected over a step period of 5% conversion. This indicates that limitations to diffusion evolve abruptly, due to autoacceleration phenomena. Furthermore, our analysis highlights how constraints evolve differently as a function of cross-link density, mainly, reduced crosslinker loading delaying the onset of severe diffusional limitations. Translating this kinetic information to large-area cure samples (26cm<sup>2</sup> disks), we highlight how varying experimental parameters including crosslinking fraction, sample thickness, inert polymer loading, and oxygen content provides insight to trends responsible for the different levels of wrinkling. From this work, we demonstrate how these parameters can be utilized in tandem to tailor scale and quality of final hierarchical surface morphologies evolved from PIPS and their associated surface properties.

Single-step, kinetically driven hierarchical wrinkle formation in photoinduced phase separating free radical polymer systems

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.