Layered liquid crystal elastomer actuators

Abstract

Liquid crystalline elastomers (LCEs) are soft, anisotropic materials that exhibit large shape transformations when subjected to various stimuli. Here we demonstrate a facile approach to enhance the out-of-plane work capacity of these materials by an order of magnitude, to nearly 20 J/kg. The enhancement in force output is enabled by the development of a room temperature polymerizable composition used both to prepare individual films, organized via directed self-assembly to retain arrays of topological defect profiles, as well as act as an adhesive to combine the LCE layers. The material actuator is shown to displace a load >2500× heavier than its own weight nearly 0.5 mm.

Fig. 1

Unloaded deformation of LCE laminates. a Chemical structures of: (1) the liquid crystal monomers (RM257, RM82) and (2) the dithiol additive. A mixture of 7:2 wt:wt of RM257:RM82 formed the basis of the liquid crystal elastomers (LCEs). b A 4 layer LCE laminate is optically clear. Scale bar is 1 cm. c The deformation of one, two, and four layer LCE laminates was measured in homogeneously aligned LCE films. 50% strain is observed in all three samples. d The height profiles for the single layer, double layer, and four layer LCE laminates are nearly identical over the 12 mm diameter of the films. Horizontal scale bar is 12 mm, vertical scale bar is 3.4 mm. e Height profiles of LCE laminates in which the individual layers were subject to directed self-assembly to organize into radial +1 topological defects. The LCE laminates were heated to 140 °C and imaged with an optical profilometer to quantify the deformation to thermal stimuli

Fig. 2

Soft weightlifting. a Prescribed director profile, to prepare a LCE films with a 2 × 2 array of radial +1 defects. b Deformation of a four layer LCE laminate lifting 28.7 g >2 mm. Scale bar is 3 mm. The LCE laminate was heated to 180 °C. c Stroke of LCE laminates under load. d The specific work of the LCE laminates is contrasted against normalized weight. Error bars represent statistical experimental error. e Three 1 × 1 cm LCE films are stacked with interfacing glass sheets, emulating a piezoelectric stack. A total of 1 g was lifted over 6 mm. Scale bar is 1 cm

Fig. 3

Actuation cycles. Four layer LCE laminate composed of layers with 2 × 2 array of +1 defects. Scale bar is 1 cm. Deformation of the four layer LCE laminate under 960 mg load was monitored a after 1 cycle, b 10 cycles (heating step), and c 10 cycles (cooling to 35 °C). d Stroke vs thermal cycle for 11 actuation cycles. Error bar is statistical accuracy of measurement

Fig. 4

Force enhancement. a Stroke as a function of load for 1 × 1 cm films patterned with 2 × 2 or 3 × 3 +1 defect arrays. b Specific work of the 2 × 2 and 3 × 3 arrays. Errors bars represent tilt of the lifted weight and range of three experiments. c Illustration of the deformation of a 1 × 1 cm, four layer LCE laminate (26 mg) lifting over 56 g of load over 0.4 mm. Scale bar is 1 cm

Fig. 5

Shape deformation under positive pressure. LCE films and laminates (10 mm diameter) patterned with +1 topological defects subsumed in the center were  heated to 100 °C in a pressure chamber (top right). Air pressure is applied on one side of the films, and the deformation measured via optical profilometry. The horizontal scale bar is 1 cm, while the height scale is 2.4 mm. The scale bar of the pressure chamber is 5 cm