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Exploiting the interplay of anisotropic diamagnetic susceptibility of liquid crystalline monomers and site selective photopolymerization enables the fabrication of 3D freeforms with highly refined microstructures. 

Contactless actuation powered using light is shown to generate torque densities approaching 10 N.m/kg at angular velocities ~10 2 rad/s: metrics that compare favorably against tethered electromechanical systems. This is possible even though the extinction of actinic light limits the characteristic thickness of photoresponse in polymers to tens of μm. Confinement of molecularly patterned developable shells fabricated from azobenzene-functionalized liquid crystalline polymers encodes torque-dense photoactuation. Photostrain gradients from unstructured irradiation segment this geometry into two oppositely curved regions connected by a curved crease. A monolithic curved shell spontaneously bifurcates into a jointed, arm-like mechanism that generates flexure over sweep angles exceeding a radian. Strain focusing at the crease is hierarchical: an integral crease nucleates at smaller magnitudes of the prebiased curvature, while a crease decorated with point-like defects emerges at larger curvatures. The phase-space of morphogenesis is traceable to the competition between stretch and bending energies and is parameterizable as a function of the geometry. The framework for generating repetitive torque-dense actuation from slender light-powered actuators holds broader implications for the design of soft, remotely operated machines. Here, it is harnessed in illustrative mechanisms including levers, lifters and grabbers that are powered and regulated exclusively using light. 

The effect of chain extender structure and composition on the thermomechanical properties of liquid crystal elastomers (LCE) synthesized using thiol-acrylate Michael addition is presented. The intrinsic molecular stiffness of the thiol chain extender and its relative molar ratio to acrylate-based host mesogens determine the magnitudes of the thermomechanical strains, temperatures at which they are realized and the mechanical work-content. A non-linear structure-property relationship emerges, wherein higher concentrations of flexible extenders first magnify the thermomechanical sensitivity, but a continued increase leads to weaker actuation. Understanding this interplay leads to a composite material platform, enabling a peak specific work production of ~2 J/kg using ~115 mW of electrical power supplied at 2 V. Composites of LCE with eGaIn liquid metal (LM) are prepared, which act as heaters, while being capable of actuation themselves. The thermomechanically active electrodes convert the electrical power into Joule heat, which they efficiently couple with the neat LCE to which they are bound. This system harnesses the nascent responsiveness of the LCE using electrodes that work with them, instead of fighting against them (or passively standing in the way). Specific work generated increases when subjected to increasing levels of load, reaching a peak at loads 260x the actuator weight. These ideas are extended to tri-layered actuators, where LCE films with orthogonal molecular orientations sandwich LCE-LM composite heaters. Torsional actuation modes are harnessed to twist under load. 

A central question for teachers is how to engage students in active reasoning while still aiming for substantial content goals. Asking students to generate and evaluate imagistic models can support both content learning and scientific thinking goals. Recent research indicates that imagery is a central component of scientific modeling (Schwartz and Heiser 2009). When discussing scientific models, teachers and students often lean heavily on words alone and overlook how modeling uses mental pictures and “mental movies.” Metaphorically, modeling processes can be thought of as occurring on a “sketch pad or video screen” of mental imagery in the student’s head. The set of strategies described here are intended to help teachers promote the kind of imagery that is used in scientific models. 

Abstract: This study investigates strategies teachers use to support mental imagery during modelbased science class discussions. A microanalysis of videos of classroom discussions was conducted in order to (1) identify and describe teaching strategies for supporting imagery; and (2) identify evidence that the students were engaging in the use of imagery as they constructed models and reasoned about competing models. This study starts from prior work on experts’ use of imagery, as well as from prior analyses of imagistic characteristics of concrete exemplars used successfully in a curriculum. Sixteen teacher support strategies for imagery are identified, along with thirteen student imagery process indicators. As the list of descriptors stabilizes, we are also identifying larger categories of descriptors—that is, structured categories of imagistic practices and categories of support. We present examples from a case study based on a transcript of a middle school discussion that served as one of the sources for our new organized set of imagery descriptors. 

Harnessing light to achieve manipulation and motility in meso and mm-scale systems offers the ability to remotely trigger actuation without requiring on-board power. Central to achieving macroscopic photomotility is the generation of asymmetric interaction between the light-responsive actuator and a substrate. Here, we demonstrate a facile route for achieving indexable, stepped translation of structures fabricated from azobenzene-functionalize liquid crystalline polymers (ALCP). The symmetry breaking in the dynamics of coiling (during irradiation) and uncoiling (when the light is turned off) as a function of the director orientation in splayed ALCP strips leads to asymmetric reaction forces in the interaction with a surface. The broken symmetry leads to directional translation of the center of mass in discrete steps for each on/off cycle of irradiation. Creating composite structures offers a route for hard-coding the trajectories of motility across a range of trajectories that are either rectilinear or curvilinear. Expanding this approach can offer a framework for achieving steerable light-powered microrobots that can translate on arbitrary surface topographies.