Two Methods to Synthesize Photo-Responsive Liquid Crystal Elastomer Thin films
Discipline: Chemistry and Chemical Sciences
Subcategory: Biochemistry (not Cell and Molecular Biology and Genetics)
Session: 1
Room: Exhibit Hall A
Nicholas Rubio - Saint Mary's College of California
Co-Author(s): Bojun Zhou, Washington State University, WA, Zoya Ghorbanishiadeh, Washington State University, WA, Ankita Bhuyan, Washington State University, WA, Mark G. Kuzyk, Washington State University, WA, Zuleikha Kurji, Saint Mary?s College of California, CA
Liquid crystal elastomers (LCEs) can serve as micro-actuators that respond to light: potentially performing work or exerting force remotely with their only source of stimulation being light. A successful photo-responsive LCE has been synthesized in our lab by covalently binding an azobenzene-containing monomer to an LCE platform designed by Chris Yakacki from the University of Colorado, Denver. However, as designed, this procedure produces thick samples (typically 1 to 2 mm) which do not have a repeatable, uniform thickness across batches. If we can synthesize thin films (0.1 to 0.2 mm), then we may be able to produce a more uniform and reliable LCE. Thin films were successfully produced using two different methods: by sandwiching the sample between two glass slides with a spacer of a known thickness (press films) and by spin coating (spin films). The use of silicone spray, teflon, parchment paper, and increased evaporation of solvent helped to create press films that were easily removable from the substrate. The press film method produced uniform films with thicknesses corresponding to the desired thickness: for example two representative films made with 0.15 mm spacers were measured to be on average, 0.133 ? 0.064 mm and 0.16 – 0.0872 mm thick, respectively. Surface treatment of spin films, on the other hand, proved difficult – each method caused the polymer to spin off the substrate. However, uniform spin films have been demonstrated (using 10 drops of LCE solution, spinning at 1000 rpm for 10-15 seconds, about 10-25 minutes after addition of catalyst). Under these conditions, relatively uniform spin films have been made with average thicknesses of 0.1036 – 0.0652 mm and 0.0947 – 0.0329 mm. Thin Films have been qualitatively shown to be photo-responsive when exposed to 450 nm (<5 W) laser light. The force output of the photoresponse was measured using a system created by Mark G. Kuzyk and his lab at Washington State University. It was found that the force of the photoresponse for a 0.25 mol % azobenzene, 0.112 mm film varied from 14 to 20 grams of force. The force output for a 0.0925 mm control thin film, without azobenzene, varied from 0 to 1 gram of force. These results show that the liquid crystal elastomer containing azobenzene has a much greater force output than a LCE without azobenzene. LCEs thus have the potential to do work since they exert a measurable amount of force. Future research will analyze the effect of film thickness on the force of the photoresponse and attempt to optimize the force to display the largest output.
Funder Acknowledgement(s): This study was supported by a grant supplement from the NSF (NSF EFRI REM 1332271) awarded to Mark G. Kuzyk of Washington State University (sub-award awarded to Zuleikha Kurji of Saint Mary's College).
Faculty Advisor: Dr. Zuleikha Kurji, zk4@stmarys-ca.edu
Role: My contribution to this research is that I optimized and refined the procedure of making liquid crystal elastomers and press films. I created the technique for synthesizing thin films through the use of a spin coater and tested different parameters until an optimal set was found. I created the thin films whose photo-response was quantitatively measured and analyzed the photoresponses of azobenzene containing thin films and films without azobenzene.