Amphiphilic Assemblies at Liquid Crystal Interfaces

Abstract

The research described in this thesis shows how nematic liquid crystals (LCs), which amplify molecular events at their interfaces, can be exploited to create responsive smart materials. This is accomplished through a series of studies aimed at developing fundamental insight into the response of LCs to amphiphilic assemblies at their interfaces. Accordingly, the research is organized into two parts. The first part of this thesis describes the equilibrium response of LCs to amphiphilic assemblies at their interfaces. We begin by showing how solvent pre-treatment reversibly induces a wide range of organizations of polypeptide brushes comprising poly(benzyl-L-glutamate) (PBLG). Subsequently, we demonstrate how LCs can be used to characterize the PBLG chain orientations within those brushes. In our second study, we show that LCs can optically report protein specific binding events to amphiphilic ligands in the presence of non-specific proteins. This was accomplished through use of modular synthetic oligomers comprising alkyl chains to anchor the oligomers to the LC interface, oligoethylene glycol to minimize interactions with nonspecific proteins, and sulfonamide moieties to specifically bind to carbonic anhydrase II. The second part of this thesis describes how non-equilibrium behaviors of LCs can provide the basis of new classes of responsive soft matter. First, we show that LCs can selectively report the assembly of amyloid oligomers over larger fibrils at aqueous-LC interfaces. Additionally, we advance our understanding of how protein phase states (i.e., solid-like vs. liquid-like) dictate the morphology of their assemblies at LC interfaces. Next, we explore the interactions of individual amphiphilic assemblies at aqueous-LC interfaces. Specifically, we describe how the collision and spreading of assemblies at aqueous-LC interfaces triggers spatially localized and transient flashes of light to be transmitted through the LC. Finally, we investigate how polyelectrolyte adsorption at aqueous-LC interfaces can trigger the ejection of microdroplets decorated with oppositely-charged surfactants, consistent with an attractive electrical double layer interaction between the elastically-trapped microdroplets and the LC interface. During microdroplet release, polyelectrolyte-surfactant complexes form at the LC interface to regulate interfacial charge at rates that reflect the dynamics of complex assembly and disassembly. Overall, these studies reveal fundamental insights that underlie new opportunities for engineering responsive smart materials based on amphiphilic assemblies at LC interfaces.