Hybrid Materials With Actuatable, Hierarchical Topography for Multifunctional Surface Design

Abstract

We rely on engineered surfaces for robust adhesion, protection and sealing, efficient heating and cooling, and control over the growth of biological species. Both in our daily lives and in industry, surfaces often serve multiple purposes simultaneously and our requirements for them can change over time, creating the need for multifunctional surfaces that can be dynamically optimized for different environments. Surfaces that can be actuated to exhibit microscale textures are a particularly interesting approach toward achieving multifunctionality as topography plays a key role in interfacial phenomena across several length scales. In fact, our understanding of the importance of surface texture in different fields has prompted a surge in the past decade in approaches for engineering surfaces with an impressive array of curvatures and hierarchical structure. However, strategies for programming surfaces that can transition from one hierarchical surface texture to another are still lacking, thus limiting the range of surface functionalities that can potentially be introduced into a single material. In this thesis, we develop novel principles for designing materials with actuatable, hierarchical topography through harnessing non-equilibrium phenomena in hybrid material systems, where stimuli-responsive soft components, which respond directly to the environment, are combined with rigid components, which modulate their response. In Chapter 2 through Chapter 5, we develop a stimuli-responsive gel-based hybrid system by covalently bonding thermoresponsive gels to a structured surface with large, rigid bumps, and show how it can be programmed to exhibit evolving, and hierarchical features that create new possibilities for colloidal and biological assembly, wetting and adhesion, and heat transfer applications. In Chapter 6, we develop a ferrofluid-hybrid system by confining magnetic ferrofluid onto a porous, microstructured surface through capillarity and show how it can be triggered to exhibit hierarchical morphologies that exhibit a wide range of switchable functionality. Throughout this thesis, we use a combination of experimental and time-resolved numerical techniques to gain deeper insight into microscale phenomena, while providing a path for determining how to program the dynamics of the systems. Moving forward, we envision that this work will provide insight into the development of more versatile and multifunctional surfaces that can truly match the sophistication of our demands.