ME Seminar Series: Super-Soft and Super-Elastic Networks
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Wednesday, September 12, 2012 - 8:30am to 10:00am
Topological entanglements between polymer chains determine a lower limit of ~105 Pa for elastic modulus of conventional elastomers. Much softer materials are needed for a number of applications ranging from implants for reconstructive surgeries and tissue growth scaffolds to antibacterial and antifouling surfaces. The traditional way of reducing the modulus is to swell polymer networks with a solvent, which, however, can diffuse out of these gels making them unacceptable for many applications. We propose several alternative routes for preparing super-soft dry networks with elastic moduli many orders of magnitude below that of conventional elastomers. These methods are based on (i) significant reduction of plateau modulus in molecular brushes with densely grafted side chains effectively acting as chemically attached solvent species and spacers between brush backbones and (ii) the absence of rubbery plateau in melts of non-concatenated entangled cyclic polymers. We predict elastic modulus (that can be much lower than kPa), maximum stretch ratio (that can be ~of the order of 100), and other mechanical properties of these super-soft and super-elastic networks in good agreement with experiment.