ETH Polymer Physics seminar


1999-12-15
16:15 at ML F 34

Mechanical Properties of Smart Ultrathin Polymer Films

Reto Luginbühl

University of Washington Engineered Biomaterials and Department for Bioengineering, University of Washington, Seattle, WA, 98195-1750

Modern biomaterial research proposes that recognition surfaces will trigger biological responses. Ideally, the material surfaces will present recognition elements directed to a specific biological function. Such surfaces may be engineered by imprinting different polymers. Smart polymers, which change their structural properties upon stimulation, are among the materials that are of highest interest for this application. In addition they might be used in biotechnology, medicine, and biomaterial settings. Progress in precision-engineered surfaces strongly depends on the development of appropriate techniques to analyze surfaces at the micro and nanometer level, as confinement effects of molecules at biomaterial interface may influence their biological response. Therefore, accessing contact mechanical properties at the interface may be as important as determination of the molecular structure. The SFM offers a unique combination of microscopy with spectroscopic analysis of surface interactions and local subsurface structural properties. Recently, considerable research effort has focused on the investigation of co-polymers and grafted polymers containing N-isopropylacrylamide (NIPAM). These polymers can be engineered to undergo thermally induced structural and mechanical phase transitions around 32 ºC. In contrast to the glass transition behavior observed in most polymeric materials, the structural phase transition of NIPAM is accompanied by a change in volume, and therefore a change in mechanical properties, as well as a change in the surface free energy. We carried out scanning force microscope (SFM) investigations on surface confined NIPAM films. Thin films (thickness << 10 nm) were obtained by plasma polymerization on selected substrates. Applications of novel SFM techniques permit the observation of the transition behavior at the nanometer scale as a function of temperature. Contact mechanical properties and interfacial energy were monitored as a function of the system temperature.


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