Fundamental Investigation into 3-D Printed Liquid Crystalline Elastomers: Orientation, Rheology, and Stimulus-Response

Bauman, Grant E.

Graduate Thesis Or Dissertation

Fundamental Investigation into 3-D Printed Liquid Crystalline Elastomers: Orientation, Rheology, and Stimulus-Response Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/np193b65s

Abstract

Liquid crystalline elastomers (LCEs) are soft materials capable of undergoing large, anisotropic deformations in response to stimulus. The compelling stimulus-response of LCEs is due to order-disorder disruption of liquid crystallinity in the polymer network. Motivated by the potential use of LCEs as material actuators in robotics, health care, consumer goods, and aerospace, this thesis presents a series of interrelated fundamental studies that generally elucidate the association of orientation, material processing, and stimuli-response in LCEs.

Specifically, the effect of molecular orientation on actuation was isolated by preparing a series of elastomers with different liquid crystalline contents using mechanical alignment. The degree of molecular ordering, measured with X-ray scattering, increased with both increasing liquid crystalline content and increased mechanical strain during polymerization. Thermomechanical characterization of these materials confirmed the magnitude and rate of deformation are linearly correlated with the degree of orientation. As in prior reports, the actuation temperature is associated with the composition (e.g., the concentration of liquid crystalline groups) of the LCE.

Further, the conditions necessary to realize high degree of molecular ordering in 3-D printed LCEs were examined in fundamental rheological studies. Flow-induced alignment is accompanied by a significant decrease in viscosity. Rather than being instantaneous, the change in viscosity occurred over an appreciable time period. The alignment of inks was systematically examined in the nematic and isotropic states.

Informed by these fundamental studies, a series of LCEs were created through mechanical alignment and 3-D printing with unprecedented low-temperature response. Through incorporation of a monomer with decreased intermolecular interactions, LCEs were synthesized that change shape in response to body heat or cooling from ambient temperature. Shape transformation of 3-D printed LCEs were also explored as haptic surfaces. Uniquely, these elements were printed with multiple materials, to realize distinctive shape transformation into 3-D shapes with raised flat surfaces.

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