Development of Model Elastomeric Photomechanical Systems and Their Characterization

Photomechanical liquid crystalline (LC) polymers have blossomed into an exciting field of innovation in recent years due to their potential for large, wireless actuation. It has been demonstrated that photochromic monomers can be integrated into a variety of these systems in a programmed way that allows for control over the material response. Many research groups have demonstrated significant photomechanical deformation of azobenzene functionalized LC polymers. However, these materials often require complicated syntheses that are difficult to scale and normally only produce movement in thin samples, restricting their usefulness for mechanical actuation. Another evident drawback to current systems is the almost exclusive use of azobenzene derivatives that absorb light primarily in the ultraviolet to blue range. At these wavelengths azobenzene experiences competitive absorption with the surrounding organic polymer network. In addition UV light has adverse effects for living tissue, and causes photo decay in polymers over time. Recently, a thiol acrylate Michael addition reaction was introduced as a simple and scalable procedure for producing liquid crystal elastomers (LCEs). The goal of the present work is to functionalize these LCEs with red to NIR absorbing dyes or dopants. To build up capability with this material, commercial azobenzene monomers and gold nanoparticles were incorporated into the LCE. Samples were characterized through photomechanical cantilever bending tests and via dynamic mechanical analysis. Future work will involve characterization of LCEs that incorporate a red-NIR azobenzene derivative that is currently under development. If successful, these light responsive systems hold great potential for utilization in biomedical systems and for the development of morphing surfaces, artificial muscle actuators, and microvalves.