Modeling the circular shear in light activated shape memory polymers with three networks

Shape memory polymers (SMP's) are polymers that have the ability to retain a temporary shape, which can revert back to the original shape on exposure to specific triggers such as increase in temperature or exposure to light at specific wavelengths. A new type of shape memory polymer, light activated shape memory polymers (LASMP's) have been developed in the past few years. In these polymers the temporary shapes are fixed by exposure to light at a specific wavelength. Exposure to light at this wavelength causes the photosensitive molecules, which are grafted on to the polymer chains, to form covalent bonds. These covalent bonds are responsible for the temporary shape and act as crosslinks. On exposure to light at a different wavelength these bonds are cleaved and the material can revert back to its original shape. A constitutive model of LASMP's which based on the notion of multiple natural configurations has been developed (see Sodhi and Rao [1]). It has been applied to model the circular shear of light activated shape memory polymer with two networks. In this work we use this model to analyze the mechanical behavior of LASMP's with three different networks undergoing a circular shear deformation cycle. This involves study of the behavior of the LASMP's when two temporary configurations are formed by exposing the polymer to light at different time during the deformation process. In addition, we show that these materials are able to undergo complex cycles of deformation due to the flexibility with which these temporary configurations can be formed and removed by exposure to light.