EAGER/RUI: One-Step, Programed Alignment of Liquid Crystal Elastomers by Guest Host Interactions

Hope College, Holland MI

Investigators

Abstract

This EArly-concept Grant for Exploratory Research (EAGER) project will demonstrate feasibility for a novel one-step printing and polymerization process for liquid crystal material. Liquid crystals are rod-like, rigid molecules that have both liquid-like (free diffusion of molecules) and solid-like properties (ordered molecular arrangements). Liquid crystal elastomers are rubbery materials made from liquid crystal repeat units connected together in long chains forming a true solid. It has been observed that when all the liquid crystal units line up in the same direction that material size changes of 300-400 percent can be produced by heating. These large, reversible deformations could be extremely useful for a variety of applications such as soft, synthetic muscle actuators or rewriteable braille displays. Unfortunately, alignment is difficult to attain while forming the material into the complex structural shapes typically required for practical devices. This award supports fundamental research to demonstrate the feasibility of a new process for aligning these materials during manufacture. This new process will enable advancement toward 3D printing of aligned elastomer materials which will empower new applications in the biomedical, aerospace, chemical, and energy industries. As a result, this work will enhance the U.S. economy, society, and global competitiveness. Additionally, this research will directly benefit the STEM workforce by enhancing engineering education and persistence to graduation among undergraduate participants at a primarily undergraduate institution. Current approaches to fabricating responsive liquid crystal elastomers rely on elaborate procedures to align the liquid crystal units that represent a serious impediment to the widespread development of these materials for practical applications. The objective of this research is to generate a one-step, facile technique for orienting liquid crystal moieties in the material bulk while simultaneously fixing the alignment through network cross-linking. The alignment will be obtained using guest host interactions between the liquid crystals and photo-responsive dopants. To produce robust alignment of the liquid crystal elastomer the various reaction processes must proceed simultaneously, but with distinct time scales. The approach for this work will involve a systematic exploration of the combined reaction kinetics in order to clarify their role in liquid crystal alignment. Kinetics will be characterized by in situ infrared spectroscopy. Aligned elastomers will be characterized by several techniques including, polarized ultraviolet-visible spectroscopy, differential scanning calorimetry, and dynamic mechanical analysis. The contribution of this research to the greater body of knowledge will be significant because it will advance understanding of how material anisotropies can be controlled in situ during manufacturing processes such as 3D printing, enabling the design of adaptive, shape-programmable structures and devices by a broad range of engineers and applied scientists.