Conversion of light into macroscopic helical motion

Abstract

A key goal of nanotechnology is the development of artificial machines capable of converting molecular movement into macroscopic work. Although conversion of light into shape changes has been reported and compared to artificial muscles, real applications require work against an external load. Here, we describe the design, synthesis and operation of spring-like materials capable of converting light energy into mechanical work at the macroscopic scale. These versatile materials consist of molecular switches embedded in liquid-crystalline polymer springs. In these springs, molecular movement is converted and amplified into controlled and reversible twisting motions. The springs display complex motion, which includes winding, unwinding and helix inversion, as dictated by their initial shape. Importantly, they can produce work by moving a macroscopic object and mimicking mechanical movements, such as those used by plant tendrils to help the plant access sunlight. These functional materials have potential applications in micromechanical systems, soft robotics and artificial muscles.

High‐Power Actuation from Molecular Photoswitches in Enantiomerically Paired Soft Springs

“…The variety of movements seen in the plant and animal kingdoms have provided inspiration for the engineering of soft robots of all kinds,9, 10, 11, 12, 13, 14 and in particular, the realization that plant mechanics often rely on dynamic helical systems15, 16, 17, 18, 19 has motivated the development of a variety of chiral actuators where molecules were used either as active transducers of energy11, 13, 20, 21 or as relays for humidity or temperature changes 22, 23, 24, 25. These soft actuators have demonstrated reversible shape transformation, work, and motility,26 but the response speed and power produced remain moderate, mainly owing to the lack of mechanisms to drive non‐linear actuation 27.…”

“…Under illumination, the trans ‐azobenzene isomerizes and induces an anisotropic deformation of the liquid‐crystal network (Figure 1 c) 35. This photomechanical property has been used to switch surface roughness36, 37 and to transform twisted shapes before 13, 38, 39. In the artificial valves that we designed, the two sets of bars undergo different shape and size modifications upon activation of 1 .…”

A monolithic hydro/organo macro copolymer actuator synthesized via interfacial copolymerization

“…The shape transformations of biological organisms [1][2][3][4][5][6] have been the inspiration for many products in the field of artificial muscles, [7][8][9][10][11][12][13] soft robotics, [14][15][16][17][18][19] sensors 20 and complex shape engineering. 21,22 For example, the leaves of the Venus flytrap snap together to capture insects by virtue of the synergy between the hydroelastic instability and asymmetric expansion of the inner and outer surfaces at the cellular level.…”

“…24,31 However, the practical applications of these actuators were limited because of the low modulus and weak mechanical strength of the hydrogels. 32 Elastomer single layer films, such as azobenzene polymer films synthesized using an elaborate molecular design, 13,27 can achieve smart responsive curving. However, these films require a unidirectional stimulus to generate anisotropic contraction/expansion of their two sides; this factor limits the film thickness to the micrometer or sub-millimeter level.…”

Photoswitchable Nanomaterials Based on Hierarchically Organized Siloxane Oligomers

“…For example, expansion of chiral nematic LCs along the helical axis has been utilized to create polymer coatings with photoswitchable topologies [14][15][16][17] and polymer films with macroscopic helical motion. [18] Additionally, polymer films with splay-bend configuration, in which LC-mesogens gradually change orientation throughout the film cross-section, have shown to exhibit inherently anisotropic bending as well as achieve significantly faster and larger bending when compared to uniaxially aligned films. [19][20][21] The ability of azobenzene photoisomerization to generate anisotropic dimension change and motion in LC networks typically results from increased molecular disorder caused by bent cis-azobenzene relative to networks with rod-like transazobenzene.…”