Taylor H. Ware

Voxelated liquid crystal elastomers

Making small actuators more effective Liquid-crystal molecules orient locally in response to external fields. When long-chain liquid-crystalline molecules are crosslinked together, changes in local orientation can lead to significant volume changes. Ware et al. made efficient microactuators that can change their shape from flat to three-dimensional structures (see the Perspective by Verduzco). By patterning volume elements so that each has a different preferred alignment for the liquid-crystalline molecules, they could fine-tune the volume changes. Science, this issue p. 982; see also p. 949 Liquid crystal elastomers are spatially patterned to create microactuators with controlled local volume changes. [Also see Perspective by Verduzco] Dynamic control of shape can bring multifunctionality to devices. Soft materials capable of programmable shape change require localized control of the magnitude and directionality of a mechanical response. We report the preparation of soft, ordered materials referred to as liquid crystal elastomers. The direction of molecular order, known as the director, is written within local volume elements (voxels) as small as 0.0005 cubic millimeters. Locally, the director controls the inherent mechanical response (55% strain) within the material. In monoliths with spatially patterned director, thermal or chemical stimuli transform flat sheets into three-dimensional objects through controlled bending and stretching. The programmable mechanical response of these materials could yield monolithic multifunctional devices or serve as reconfigurable substrates for flexible devices in aerospace, medicine, or consumer goods.

Programmed liquid crystal elastomers with tunable actuation strain

The ability to program the local mechanical response of liquid crystalline polymer networks has been shown to generate complex mechanical responses. A facile two-step method to synthesize these anisotropic materials to realize either reversible or irreversible shape change behavior is reported. The first reaction is the addition of a nematic diacrylate to a primary amine to build macromers within a liquid crystal alignment cell. Subsequently, these macromers are crosslinked to trap the order of the liquid crystal into a crosslinked film. In unaligned samples, mechanical reorientation of the nematic director is used to isothermally program shapes at room temperature that can be recovered on heating. Under a load, the mechanically aligned materials exhibit tensile actuation behavior comparable to human skeletal muscle in stroke and specific work capacity. We also report spatially aligned films that reversibly morph from flat to a complex 3D shape with tunable strain from 3% to 55%.

Encoding Gaussian curvature in glassy and elastomeric liquid crystal solids

We describe shape transitions of thin, solid nematic sheets with smooth, preprogrammed, in-plane director fields patterned across the surface causing spatially inhomogeneous local deformations. A metric description of the local deformations is used to study the intrinsic geometry of the resulting surfaces upon exposure to stimuli such as light and heat. We highlight specific patterns that encode constant Gaussian curvature of prescribed sign and magnitude. We present the first experimental results for such programmed solids, and they qualitatively support theory for both positive and negative Gaussian curvature morphing from flat sheets on stimulation by light or heat. We review logarithmic spiral patterns that generate cone/anti-cone surfaces, and introduce spiral director fields that encode non-localized positive and negative Gaussian curvature on punctured discs, including spherical caps and spherical spindles. Conditions are derived where these cap-like, photomechanically responsive regions can be anchored in inert substrates by designing solutions that ensure compatibility with the geometric constraints imposed by the surrounding media. This integration of such materials is a precondition for their exploitation in new devices. Finally, we consider the radial extension of such director fields to larger sheets using nematic textures defined on annular domains.

Inverse Design of LCN Films for Origami Applications Using Topology Optimization

Liquid crystal polymer networks (LCNs) have unique advantages as potential constituents of origami-based smart materials due to their reversible actuations and availability of fabrication techniques to create complex strain fields. Although identifying functional designs is crucial in making use of this technology, conventional approaches have largely consisted of trial-and-error experimentation. We introduce an inverse design procedure based on a topology optimization method to map out an LCN pattern with a desired spontaneous strain field to achieve prescribed shapes. In this study, we focus on a target deformation of a film to create an improved hinge to be integrated into an origami structure. Our preliminary results indicate the potential of using computational tools to determine what designs yield desired functionalities and how to best pattern LCN films to achieve them.Copyright

Novel reconfigurable antennas using Liquid Crystals Elastomers

In this paper, normal and axial mode reconfigurable antennas are considered. Shape memory polymer actuators called Liquid Crystal Elastomers (LCEs) are used to dynamically change antennas. Specifically, a controlled heat source is utilized to the geometry of antennas. The proposed antennas were fabricated to fixed states to allow measurements to be performed and illustrate the antenna reconfigurability between normal and axial mode. Measurements are compared with simulations.