题  目：Dynamics and mechanical properties of gels with physical and chemical crosslinks
报告人：Prof. Creton Costantino, (Laboratory of Soft Matter Science and Engineering, ESPCI, Paris
时  间：2014年1月14日 下午 13:00
地  点：beat365A楼会议室
邀请人：周永丰 教授

报告摘要：

    We studied the stress strain relation and the fracture properties of model polyvinyl alcohol dual cross-link hydrogels having permanent (glutaraldehyde) cross-links and transient (Borax solution) cross-links. Depending on the relative concentration of the physical and chemical crosslinks, the mechanical properties are significantly changed. We investigated the stress strain relation over an unusually wide range of extension ratios and strain rates and combined these experiments with fracture toughness experiments on notched samples carried out over three decades of strain rates. These results are interpreted with the help of dynamic experiments carried out at small strain by light scattering and rheology. We proposed a new analysis method to separate the stress into strain and time dependent terms. The strain dependent term is derived from rubber elasticity while the time dependent term is due to the failure of transient cross-links and can be represented as a time dependent shear modulus which shows the same relaxation as in small strain. This new analysis method should have a wide applicability not only for hydrogels but also for other highly viscoelastic soft solids such as soft adhesives or living tissues and stresses the need to investigate the strain rate dependence of the mechanical behavior in soft materials.