Using Small Molecule Absorbers to Create a Photothermal Wax Motor

Abstract

Organic phase change materials are used in actuators like wax motors. The solid→liquid phase transition that drives expansion is commonly induced by resistive heating that requires an electrical connection. The use of light to generate a phase change provides a non‐contact way to power wax motors. Here, it is demonstrated that small molecules can act as absorbers to enable a photoinduced solid→liquid melting transition in eicosane, a low molecular weight phase change material. Three different small molecule absorbers are utilized: (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO), azobenzene (AZOB), and guaiazulene (GAZ). The GAZ/eicosane mixture is characterized in detail because its absorption extends out to 750 nm, opening up the possibility of using near‐infrared diodes as the photon source. The GAZ/eicosane composite is incorporated into a commercial wax motor assembly and 532 nm laser light is used to lift up to 400 g. The temporal response, work and force output, and efficiency are measured, and no loss of lifting capability or degradation is observed after ten cycles of irradiation. The incorporation of small aromatic molecules with low‐energy absorption features into phase change materials can provide a general way to make light powered wax motors.

Optically Controlled Solid-to-Liquid Phase Transition Materials Based on Azo Compounds

“…Due to the synergistic effect between molecules, the photoisomerization of azo compounds not only can regulate their own phase change behaviors but also act as a photoswitch to control the phase states of photoinactive materials. Following this principle, the combination of azo compounds with conventional organic PCMs 61,62 or biomaterials 114 has also afforded the photochemical solid−liquid transition properties. Conventional organic PCMs are excellent for latent heat energy storage, but it is a pity that they do not respond directly to photons.…”

“…They have successfully realized photocontrollable adhesion, , coining, self-healing, and other functions. It has been proven that this material system can provide both the benefits of photomanipulation of light responsive materials and the functional advantages of PCMs. , In addition, the molecular length and energy level differences between the cis and trans isomers of azo compounds continue to play an important role in OPTMs, enabling them to possess more advantages than non-phase transition azo materials in the fields of photoactuators and solar thermal fuels (STFs). , …”

“…It has been proven that this material system can provide both the benefits of photomanipulation of light responsive materials and the functional advantages of PCMs. 61,62 In addition, the molecular length and energy level differences between the cis and trans isomers of azo compounds continue to play an important role in OPTMs, enabling them to possess more advantages than nonphase transition azo materials in the fields of photoactuators 63 and solar thermal fuels (STFs). 64,65 Because OPTMs have demonstrated their great potential in practical applications, it is necessary to study such materials comprehensively.…”

Azobenzene Based Photo-Responsive Hydrogel: Synthesis, Self-Assembly, and Antimicrobial Activity

“…In recent years, LMWG-responsive hydrogels have been developed due to the integration of more controllable properties and functions. Generally, LMWGs are formed by various supramolecular forces, such as π-π stacking, hydrogen bonding, hydrophobic forces, and electrostatic interaction [ 4 , 5 ]. Typical LMWGs include amino-acid derivatives, carbohydrates, and peptides.…”

Analysis of molecular photomechanical performance using a one-dimensional harmonic model

“…Photomechanical materials have the property that their constituent nuclei change position after photon absorption, generating a force and displacement that can be harnessed to perform mechanical work [1][2][3]. This change in atomic coordinates could result from heating (photothermal) [4][5][6], a change in electronic state (photostrictive) [7], or a chemical reaction (photochemical) [8].…”