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Electro-Responsive Polymer Boundary Lubricants

Directeur de thèse : Carlos Drummond

Anchoring of polymer or polyelectrolyte chains at solid-surfaces is an efficient way to modify their interfacial properties in an aqueous environment. Polymer layers Immobilized at the interface affect the stability and rheology of colloidal dispersions, the lubrication properties and the biocompatibility of artificial surfaces. By manipulating the chain conformations by external stimuli one can control the effective interactions and thus efficiently tune viscoelastic properties of dispersions, lubrication, etc. The main objective of the proposed project is to explore experimentally novel design strategies of smart surfaces operating in contact with aqueous media. We search for systems where structure and properties can be reversibly switched by applied external physical and chemical fields. The manipulation of the conformations of grafted polyelectrolyte chains by an applied electrical field, although very attractive for application purposes, still remains a challenging experimental task.

The possibility of triggering conformational transitions in surface-attached polymeric layers by external physical (temperature, electrical voltage, light, etc.) or chemical (pH, salinity, solvent composition, etc.) fields opens new perspectives for design of stimuli-responsive (“smart”) interfaces. Polymers for responsive coatings operating in contact with aqueous environment should have sensitive moieties. Polyelectrolytes, and in particular pH sensitive (weak) polyelectrolytes are attractive candidates for this task : their conformations can be modified by such stimuli as pH, salinity or electrical fields.

The interaction between two surfaces immersed in 10mM NaNO3 is modified by the application of an alternating electric field. The electric field induced force is initially attractive, as a consequence of the opposite electric charge of the electrodes, and then repulsive, as a consequence of the slow redistribution of ions between the surfaces.

Self Assembled films of polylysine on gold. The morphology of the SAM depends on the voltage applied to the tip in the Scanning Tunnelling Microscopy Imaging. The properties of the SAM coated surface will depend on the morphology of the adsorbed layer.