Model Studies of Reversibly Interacting Surfaces

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The PI proposes to study interactions between surfaces and interfaces to which well-characterized distributions of adhesion molecules have been added. The molecules are based on block copolymers consisting of hydrophobic and hydrophilic portions that are localized at a solid/liquid or liquid/liquid interface. Experiments are designed to study a variety of attractive interactions between two such interfaces in aqueous media. These attractive interactions are reversible, and result from specific interactions between functional groups attached to the hydrophilic portions of the block copolymers. Proposed experiments include studies of hydrophobic interactions between functional groups that are attached to the ends of the polymer chains, hydrogen-bonding interactions between functional groups that are attached to the ends of the polymer chains, and strong hydrogen-bonding interactions between a model receptor/ligand pair that has been well-characterized by the biophysics community. The experiments will determine the ways that collective forces from individual adhesion molecules result in quantifiable attractive interactions between surfaces bearing multiple adhesive groups. The proposed research will define the role of the surface, the effects of spatial distribution of adhesive molecules (uniformly distributed or clustered) and the lateral mobility of the adhesive molecules in the plane interface. A series of contact experiments have been designed that are sensitive to interfacial interaction energies spanning several orders to magnitude.The research provides a necessary link between the molecular-level information that is becoming increasingly available as a result of recent advances in nanoscience and nanotechnology, and the information that is needed for the appropriate design of biomaterials or self-assembling systems, where the relevant length scales are often in the micron range. Development of experimental methods and theoretical models that can be utilized to make this connection between 'nanoscopic' and 'microscopic' properties will be an important outcome of this research. A micromechanics laboratory with enhanced capabilities for studies of 'soft' materials will also be available to scientists throughout Northwestern University and the their collaborators. In addition, graduate and undergraduate students will be trained in aspects of surface science and mechanics, and in both physical and chemical aspects of polymer science.