(45d) Designing Biomimetic Polymeric Interfaces: Using Photopolymerization Techniques to Simultaneously Control Surface Chemistry, Topography and Functionality

There exist numerous examples of natural surfaces with unusual interfacial behaviors, such as the lotus leaf, which strongly repels water, to the shell of the Namib desert beetle which facilitates water capture and collection in arid climates. These interfacial designs are useful for engineering applications such coating development, water purification, and beyond. Through observations of natural surfaces, it has been established that both surface chemistry as well as topological features ranging in scale from nanometers to microns play an equally significant role in interfacial interactions. However, knowing the importance of these combined influences, the current challenge is identifying versatile and efficient methods for materials development that afford control over both surface chemistry and topography. Here we explore the use of photopolymerization-based approaches to engineer surfaces that address the need for both topological features and chemical patterning. To create rough, topographical features, we show how polymerization-induced shrinkage can be exploited to create patterned structures across an interface, without the need of a template nor additional processing. Furthermore, we show how this mechanism alone can significantly alter macroscopic surface/fluid interactions, at times transforming an intrinsically hydrophilic polymeric material (water contact angle <90°) to an interface that is strongly hydrophobic (water contact angle ~ 130°). To manipulate surface chemistry and the patterning thereof, we designed multi(acrylate)/prepolymer resins that undergo thermodynamically driven de-mixing across an interface, allowing for local variations in composition of the surface material. Furthermore, we show how polymer/substrate interactions as well as polymer macromolecular structure can be engineered to manipulate the segregation of certain moieties towards the air/polymer interface, further demonstrating control over the surface chemistry. While segmental diffusion to the air/polymer interface is typical for low-surface energy materials (fluorinated compounds, etc.) we show how precise design of polymer chain ends can promote the diffusion of higher surface energy materials with hydrophilic nature towards this interface. These combined studies are particularly relevant as photopolymerizations are an attractive approach to address the need for robust and complex interfaces with easily tunable properties. Photopolymerizations offer both spatial and temporal control over surface fabrication and are an energy efficient methodology, particularly when compared to thermal-based processes. These advantages, along with the fact that both the need for specific chemistries and three-dimensional features can be addressed with this technique, make photopolymerizations a viable alternative when addressing large scale needs for interfacial materials.