DESIGN AND HIERARCHICAL ASSEMBLY OF AMPHIPHILIC SUPRACOLLOIDS THAT MIMIC BIMOLECULAR COMPOUNDS

Abstract

Self-assembly of nanoparticles (NPs) into desired structures with precisely controlled NP organization is crucial to the property discovery and application of inorganic NPs. Despite tremendous efforts made in the past decades, little progress has been achieved in controlled hierarchical assembly of NPs. My dissertation is focused on the multi-level assembly of inorganic NPs into various hierarchical structures by tethering NPs with functional block copolymers (BCPs).

First, one versatile strategy was developed to design monodisperse amphiphilic supracolloids with defined valence and chemical patches by co-assembly of binary disparate hybrid building blocks composed of BCP-functionalized NPs. The binary BCP is composed of a hydrophilic/hydrophobic block and a Lewis base-containing/Lewis acid-containing block. The resulting supracolloids consist of two different types of inorganic NPs precisely arranged in space, which mimics the geometric shape and valence of bimolecular compounds containing two elements. By varying the size, chemical composition and feeding ratio of NPs, as well as the length of BCP combinations, supracolloids with different valences, compositions and localized chemical patches (which are determined by the BCP tethers) were produced in high yield.

Second, the amphiphilic supracolloids were demonstrated to assemble into a range of two-dimensional (2D) hierarchical structures at the liquid/liquid interface. Depending on the quality of solvent, amphiphilic dimers were found to assemble into petal-like structures with different numbers of dimers. Moreover, amphiphilic trimers underwent side-by-side or end-to-end association to form ribbon or chain structures, depending on the arrangement of hydrophilic and hydrophobic domains (chemical patches).

Third, the effect of polymer length of BCP tethers within supracolloids was systematically studied on the ribbon formation of trimer-like supracolloids with hydrophobic center and hydrophilic ends. It was found that longer hydrophobic block and shorter hydrophilic BCP tethers facilitate the formation of ribbon. The results were summarized in a product diagram.

Finally, the pH effect on the assembly of amphiphilic supracolloidal trimers was investigated. A transition of assembly morphologies from ribbons to chains was observed, with changing pH of the water phase. This can be attributed to the change on the amphiphilicity of supracolloidal trimers upon the addition of acid or base.