Developing a General Interaction Potential for Hydrophobic and Hydrophilic Interactions in Self-Assembled Systems.

摘要

In self-assembled systems such as micelles, vesicles, lipid bilayers, biological membranes, and proteins, the intermolecular interactions between aggregates and within individual aggregates determine the structures, properties, and functions of such systems. These interactions can include long range interactions, such as van der Waals, electrostatic double layer, polymeric (steric), hydration, and hydrophobic interactions, or shorter-ranged specific interactions such as hydrogen bonding, coordination bonds, and ligand-receptor binding. Understanding of the range and magnitude of such forces, which can be understood in terms of inter-particle or intermolecular interaction potentials, is important for controlling and engineering desired system properties.;Two of the most important interactions in aqueous solutions, hydrophobic and hydrophilic interactions, do not have widely accepted, simple, analytical interaction potentials. Hydrophobic interactions are attractive forces that arise between hydrophobic surfaces due to the inability of water to form a hydrogen bond network near an extended hydrophobic interface. Conversely, hydrophilic interactions (also known as hydration forces) are repulsive forces that occur upon confining hydrated surfaces. In this thesis, direct force measurements between hydrophobic and hydrophilic surfaces in several different self-assembled systems are used to empirically derive and describe a general interaction potential that can account for the attractive forces due to hydrophobic surfaces as well as the repulsive forces due to hydrated surfaces. The generality of the interaction potential is illustrated by quantitative analysis of several systems, including light-responsive surfactant bilayers, self-assembled nanoparticle aggregates, and silicone coated surfaces. These systems all have a complicated combination of hydrophobic and/or hydrophilic interactions in the presence of other conventional interactions such as van der Waals, electrostatic, polymeric, or hydrogen bonding interactions. It is demonstrated herein that both hydrophobic and hydrophilic interactions can be quantified with the same general form of interaction potential: an exponentially decaying interaction with pre-exponential factor depending on the hydrophobicity or hydrophilicity of the surfaces. The hydrophobic/hydrophilic interaction potential allows for a quantitative description of interaction forces between surfaces at all distances that can describe complex structural transformations, unique aggregation behaviors, and adhesion phenomena in aqueous self-assembled systems.