Discipline: Chemistry and Chemical Sciences
Subcategory: Materials Science
Katherine Knox - California Institute of Technology
Liquid-crystal elastomers (LCEs) are a class of soft solids which exhibit a combination of the elastic behavior of rubber with the orientational order of liquid crystals. LCEs have found use as actuators due to their ability to reversibly respond to stimuli such as changes in temperature or incidence of light. The reversible nature of the shape change depends on LCEs ability to return to an ordered state after removal of the stimulus, which, in addition to their flexibility, low weight, and low power needs for actuation makes them ideal for biomedical applications.
We synthesized a main chain LCE using a two-stage thiol Michael addition, followed by additional cross-linking by exposure to UV light, based on work by Chris Yakacki’s group at the University of Colorado, Denver. The azobenzene-containing dye, disperse red 1 acrylate (DR-1A), was added as a monomer to induce a photoresponse in the LCE. DR-1A responds to green light (peak absorbtion at 492 nm) by undergoing a conformation change from the trans- isomer to the cis-isomer, and has been shown to induce bending LCE materials.
Because the DR-1A can act as a plasticizing agent, this thiol-Michael system needed to be re-optimized after after its inclusion. Monomer ratio (thiol croslinker to polymer extender) , catalyst amount concentration, UV light exposure time, and amount of DR-1A added were optimized to result in reliable and repeatable LCEs that were flexible, non-sticky, elastic and stretchy.
Photoactuation of LCEs with 0.01 mol% to 15 mol% DR-1A will be confirmed by visual observation and quantified by image analysis of video and direct measurement using a force sensor.
Resources: Chandrasekhar, S. Liquid Crystals (2nd ed.).1992. Cambridge: Cambridge University Press. ISBN 0-521-41747-3.
Yakacki, C.M. & Saed, M, & Nair, D.P, & Gong, T, & Reed, S.M, & Bowman, C.N. ?Tailorable and programmable liquid-crystalline elastomers using a two-stage thiol-acrylate reaction.?, 2015, RSC Adv. 5. 189997-190001.
Kondo, M., Yu, Y. and Ikeda, T. (2006), How Does the Initial Alignment of Mesogens Affect the Photoinduced Bending Behavior of Liquid-Crystalline Elastomers?. Angewandte Chemie International Edition, 45: 1378?1382. doi:10.1002/anie.200503684
Funder Acknowledgement(s): This work was funded by NSF EFRI ODISSEI Award 1332271, awarded to Peter Palffy-Muhoray, Ryan Hayward, Julie A. Kornfield, and Mark G. Kuzyk.
Faculty Advisor: Julie Kornfield, firstname.lastname@example.org
Role: All of it.