Modeling Photoresponsive Liquid Crystal Polymer Networks: Auto

Modeling Photoresponsive Liquid Crystal Polymer Networks:
Auto-origami with Blueprinted Director Gradients and Defects
Andrew Konya, Vianney Gimenez-Pinto, and Robin Selinger*
Liquid Crystal Institute, Kent State University, Kent, OH 44236 USA
Photoresponsive liquid crystal polymer networks (LCN) are soft nematic solids that, under illumination,
shrink along the material’s local nematic director and expand in orthogonal directions. A non-uniform
director field may be imposed when the material is cross-linked, a process known as “blueprinting,” by
forming the sample between substrates decorated with surface anchoring domains. Illuminating the
polymerized sample (or any other stimulus that reduces nematic order, such as heating) induces nonuniform mechanical strain, causing the sample to buckle, twist, curl, or fold. The 3-D blueprinted
director field, together with the sample’s initial shape and aspect ratio, thus encode a deformation
trajectory, a form of programmed auto-origami.
One key theoretical goal is to discover design principles to create blueprinted LCN structures that
function as actuators, pumps, apertures, or other simple devices. With this goal in mind, we use 3-d
finite element elastodynamics simulation to explore actuation mechanisms induced by a wide variety of
blueprinted director fields. Topological defects in the director field induce an initially flat sample to
buckle out-of-plane, forming structures with Gaussian curvature. We model LCN with high order
topological defects (from +10 to -10) and defect arrays, and compare to recent experiments by
McConney et al [1]. We also model blueprinted structures with patterned twisted domains which form
tear-drop shaped accordion folds, and compare to experiments by de Haan et al [2]. We also examine
auto-origami structures proposed by Modes and Warner [3].
Simulation studies of LCN actuation—Left:
Thin film with a single +4 topological defect
buckles out of plane. Right: Checkerboard
director field with a pattern of +/- 1 defects
and simulation of resulting actuation.
We demonstrate creation of bas relief actuator by blueprinting between non-identical substrates, and
open/close of iris-like apertures. Our finite element code, developed in-house, is implemented in CUDA
for execution on a GPU enabled computer. These results show promise for future LCN applications.
Simulation studies of LCN actuation—Left: Bas relief actuator, formed by blueprinting between
substrates with planar/homeotropic domains. Right: Chiral iris closes under illumination or heating.
References:
[1] M. E. McConney, A. Martinez, V. P. Tondiglia, K. M. Lee, D. Langley, I. I. Smalyukh, and T. J.
White, Adv. Mater. 25 (41): 5880-5885 (2013).
[2] L.T. de Haan, V. Gimenez-Pinto, A. Konya, T.S. Nguyen, J.M.N. Verjans, C. Sánchez Somolinos,
J.V. Selinger, R.L.B. Selinger, D.J. Broer, and A.P.H.J. Schenning, Adv. Funct. Mater. (2014, in press.)
[3] C. D. Modes and M. Warner, Phys. Rev. E 84 021711 (2011).
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* presenting author; E-mail: [email protected] . Work supported by NSF-DMR 1106014

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