Generating Photonastic Work from Irradiated Dyes in Electrospun Nanofibrous Polymer Mats

Abstract

For solar-driven macroscopic motions, we assert that there is a local heating that facilitates large-scale deformations in anisotropic morphologic materials caused by thermal gradients. This report specifically identifies the fate of heat generation in photonastic materials and demonstrates how heat can perform work following excitation of a nonisomerizing dye. Utilizing the electrospinning technique, we have created a series of anisotropic nanofibrous polymer mats that comprise nonisomerizing dyes. Polymers are chosen because of their relative glass transition temperatures, elastic moduli, and melting temperatures. Light irradiation of these polymer mats with an excitation wavelength matching the absorption characteristics of the dye leads to macroscopic deformation of the mat. Analysis of still images extracted from digital videos provides plots of angular displacement vs power. The data were analyzed in terms of a photothermal model. Analyses of scanning electron microscopy micrographs for all samples are consistent to local melting in low T g polymers and softening in high T g polymers. Dynamic mechanical analysis allowed for quantification of the modulus change under a given light fluence. We employ these data to calculate a energy conversion efficiency. These efficiencies for the polymer mats are compared to other nonmuscular systems, including a few natural, biological samples.

Role of Material Composition in Photothermal Actuation of DASA-Based Polymers

“…To boost the actuation potential of the active layer, additives including carbon-based materials, , gold nanoparticles, , and organic dyes are often added to enhance the conversion of light energy into heat. Among additives, photoswitches offer particular benefits in energy conversion, tunability, and high compatibility in soft materials. , A visible-light-responsive bilayer actuator system driven by the photothermal properties of a unique molecular photoswitch: donor–acceptor Stenhouse adduct (DASA; Figure a) was recently developed by our groups.…”

Photothermal Nanomaterials: A Powerful Light-to-Heat Converter

“…Plasmonic nanoparticles, carbon nanomaterials, and organic photothermal agents have been incorporated into the matrices of shape-memory polymers, − liquid crystals, − hydrogels, ,− elastomers, , and biopolymers , to form photothermal actuators and robots. The photothermal conversion by light-absorbing materials leads to basic mechanical deformations, such as bending, twisting, rotating, and jumping, of thermally responsive components to function as grippers, mills, swimmers, and syringes. ,,− Light-absorbing materials also serve as thermally responsive components in some actuators. − Several metrics, including the generated stress and strain, Young’s modulus, durability, response time, and energy consumption, have been taken into account during the design of photothermal actuators and robots. − Two types of Au nanocrystals, nanospheres and nanorods have been selectively dispersed into thermoplastic polyurethane shape-memory polymer films with a transition temperature of 55 °C (Figure a) . The sizes of the Au nanospheres and nanorods are carefully adjusted so that their LSPR wavelengths are matched with those of two light-emitting diodes at 530 and 860 nm, respectively.…”

Exploring Differences in Lanthanide Excited State Reactivity Using a Simple Example: The Photophysics of La and Ce Thenoyltrifluoroacetone Complexes

“…One of the fundamental goals in the field of photochemistry is the utilization of photons (i.e., quanta of light) to perform chemical work. These chemical transformations have been applied to various applications ranging from chemical separations , to solar energy storage, , solar fuels, – photomechanical, – and photovoltaics. – The underlying mechanism that unites all of these concepts is the promotion of an electron from the thermodynamic ground state (GS) to the excited state (ES), generating a more reducing electron or oxidizing hole. In order to enhance the desired photochemical or electron transfer properties of the excited electron or hole, ligand or functional group substitutions can be performed that alter the gradients along the ES potential energy surface (PES).…”