Photo-Responsivity Improvement of Photo-Mobile Polymers Actuators Based on a Novel LCs/Azobenzene Copolymer and ZnO Nanoparticles Network

Abstract

The efficiency of photomobile polymers (PMP) in the conversion of light into mechanical work plays a fundamental role in achieving cutting-edge innovation in the development of novel applications ranging from energy harvesting to sensor approaches. Because of their photochromic properties, azobenzene monomers have been shown to be an efficient material for the preparation of PMPs with appropriate photoresponsivity. Upon integration of the azobenzene molecules as moieties into a polymer, they act as an engine, allowing fast movements of up to 50 Hz. In this work we show a promising approach for integrating ZnO nanoparticles into a liquid crystalline polymer network. The addition of such nanoparticles allows the trapping of incoming light, which acts as diffusive points in the polymer matrix. We characterized the achieved nanocomposite material in terms of thermomechanical and optical properties and finally demonstrated that the doped PMP was better performing that the undoped PMP film.

Development of LCEs with 100% Azobenzene Moieties: Thermo-Mechanical Phenomena and Behaviors

“…To evaluate the orientational order of the mixture of LC monomers, we estimated the order parameter using linear dichroism measurements by transmission of light through the sample, with a set-up composed of: polarized laser (wavelength 633 or 457 nm), a heater chamber with an optical window (Mettler Toledo FP82HT), and a power detector (Coherent Model M-2). To evaluate the order parameter from polarized transmitted light, we used the dichroic ratio as reported in Equation (1) [ 10 ], with a transition moment parallel to the principal axis of the molecules: where A⊥ and AII are the absorbances of the cell containing the molten monomers mix, which have a director (defined as the mean value of the directions of the molecular long axes) n perpendicular or parallel, respectively, to the direction of the laser polarization. The absorbance was calculated as: , where T represents the cell transmittance.…”

“…One of the most investigated photo-responsive liquid crystalline molecules is the azobenzene [ 5 , 8 , 9 , 10 , 11 ] that isomerizes between trans (E) and cis (Z) configurations [ 12 , 13 ] when stimulated by polarized light. This isomerization can be exploited to use azobenzene as an engine to impart phototropic properties to materials.…”

Visible photomobile response of azobenzene-based polymer/carbon black films

“…This opens the way across innovative applications in several fields: soft robotics, microfluidic devices, energy harvesting, etc.. For these reasons in recent years several scientific works have been focused on the possibility to use light as energy source to drive movements for microscale devices based on polymeric materials [1][2][3][4][5][6][7][8][9]. The most common way to obtain the direct conversion of light into mechanical work is based on the use of a kind of liquid crystalline polymer bounded with azobenzene moieties [9][10][11][12]. The mechanism responsible for the light-induced bending of azobenzene-based liquid crystal PMP films (azo-LC-PMP) is the cis-trans photo-isomerizations leading to the film deformation up to a macroscopic level [10][11][12].…”

“…The most common way to obtain the direct conversion of light into mechanical work is based on the use of a kind of liquid crystalline polymer bounded with azobenzene moieties [9][10][11][12]. The mechanism responsible for the light-induced bending of azobenzene-based liquid crystal PMP films (azo-LC-PMP) is the cis-trans photo-isomerizations leading to the film deformation up to a macroscopic level [10][11][12]. This is a cooperative process that can be obtained by UV light irradiation that converts the more stable trans isomer of azobenzene in cis one.…”

“…The process is reversible because cis azobenzenes isomerize back to their trans forms upon irradiation with visible light or heating and the sample returns to the initial state. Different azo-LC-PMPs have been produced and among them, polyacrylates that bear azobenzene moieties in side chains have also been extensively studied [10,[14][15]. A very interesting challenge is to expand the spectra of absorption of azo-LC-PMP films from the UV range to the visible wavelengths because it could allow in the future to trigger different microdevices with the most important, green, renewable and low-cost radiation, the solar light.…”