Surface Micelles: Towards Controlling Morphology And Enhancing Stability

Amphiphilic molecules (including lipids, surfactants, and block copolymers,etc.) are a kind of self-organizing building blocks which have attracted increasinginterests from basic researches and various applications. Up to now, the researcheson amphiphilic molecules have developed from traditional colloid and interfacescience to many application fields such as mimicking biological membranes,catalysis, drug delivery, templating synthesis of mesoporous inorganic materialsand low-dimensional functional nanomaterials. However, the knowledge onsurfactant self-organization at solid/liquid interfaces is still limited and immature,including the structural characterization, morphology controlling, the stability andfunctionalization of surfactant aggregates at the interfaces. How to enhance thestability of surfactant self-assemblies at interfaces, especially how to stabilizesurface micelles and further control their morphologies, has become a criticalissue remaining unaddressed. In this thesis, we first designed and synthesized two kinds of amphiphiles: abolaamphiphile containing mesogenic groups, and a low-molecular-weightsurfactant with a polymerizable group at the end of its hydrophobic tail.Accordingly, we developed two methods to stabilize surface micelles through π-πstacking among mesogenic groups of the bolaamphiphile, and alternatively,through in situ polymerization of surface micelles.1. We proposed a novel method to stabilize surface micelles by introducing mesogenic groups into bolaamphiphiles, and thoroughly studied the supramolecular structures and self-organized behavior of the synthetic bolaamphiphile at interfaces using AFM as the main characterization tool. The π-π stacking among biphenyl mesogenic groups greatly enhanced intermolecular interaction within the bolaamphiphile micelles. As the result, 792004 吉林大学硕士学位论文 王明锋 we successfully obtained stable micellar structures both at the mica/water interface and in the dry state. We proposed and proved the cylindrical micelle model and the adsorption mechanism of the bolaamphiphile at the solid/liquid interface. Our results provided direct evidences for previous theoretical studies on formation, aggregate morphology and supramolecular structure of micelles.2. Using the synthetic polymerizable surfactant, we developed a unique and feasible method to stabilize surface micelles by in situ intra-micellar polymerization initiated by γ-irradiation. In situ AFM provided direct evidences that cylindrical surface micelles can remain their structures with enhanced stability after the polymerization. The enhanced stability of surface micelles is important for the detailedcharacterization of their supramolecular structures and interfacial self-organizedbehavior. Furthermore, since the robust surfactant self-assemblies with awell-defined domain size and shape on the nanometer scale at interfaces, it is apromising template for the synthesis of functional nanomaterials and thefabrication of nanopatterning architectures through an "engineering up" approach.