Optimization of PMP films’ production and mechanical properties based on ZnO nanoparticles addition

Abstract

In the last decade, smart materials have been developed in the fields of optical machines, sensors, motors, robots, and energy harvesting. This is due to their capability to respond to external stimuli or environmental changes. Among smart materials, photo-mobile polymers (PMPs) based on liquid crystals are the most promising in the field of photo-responsive actuators. These polymers are made with a mixture of liquid crystals containing azobenzene moieties that can undergo photoisomerization from trans to cis under UV light. This process leads to a macroscopic bending of the PMPs, which transforms light into mechanical energy. To enhance the PMPs' actuation, a novel liquid crystal nanocomposite is proposed. In our work, the nanocomposites are prepared with different concentrations of ZnO nanoparticles (NPs) embedded in the cross-linked polymer matrix. We have demonstrated that ZnO NPs improve the actuation and mechanical properties of the PMP, and the main aim of this assay is to optimize such effect as a function of the nanoparticles concentration. We also show the lowest and highest amounts of ZnO needed to enhance the bending behavior of the PMP. Optical, mechanical, and thermal analyses were performed to characterize the PMPs. Spectral characterization in UV/vis range of the bare and doped films, optical and atomic force microscopy, were used to comprehend the role of ZnO nanoparticles and their distribution among the liquid crystals. To study the dynamic response of the PMPs and their mechanical properties, lasers at different wavelengths were used.