Light activated shape memory polymers: Some inhomogeneous deformation examples

Shape memory polymers (SMP's) belong to a large family of shape memory materials, which are defined by their capacity to store a deformed (temporary) shape and recover an original (parent) shape. SMP's have the ability to change size and shape when activated through a suitable trigger. This trigger, which can be heating the polymer or exposing it to light of a specific frequency, is responsible for the new temporary shape. Return to the original shape can be achieved by a suitable reverse trigger. Light Activated Shape Memory Polymers (LASMP) are recently developed smart materials which are synthesized with special photosensitive molecules. These molecules when exposed to Ultraviolet (UV) light at specific wavelengths, form covalent crosslinks that are responsible for providing LASMP with their temporary shape. Light activation removes temperature constraints faced by thermoresponsive SMP for medical applications and also brings the added advantage of remote activation. Thus LASMP find use in a variety of applications ranging from MEMS devices to widespread usage for biomedical devices such as intravenous needles and stents. Furthermore, the aerospace industry has found use for these materials for applications ranging from easily deployable space structures to morphing wing aircraft. The authors have introduced a constitutive model to model the mechanics of these LASMP [1]. The modeling is done using a framework based on the theory of multiple natural configurations. A few homogenous and inhomogeneous examples were solved in [1], but with tacit understanding that the intensity of light and hence the extent of reaction is homogenous throughout the polymer sample. In this paper we use the developed model to solve the cases of inhomogeneous deformation with inhomogeneous exposure to light.