Abstract
The actuation of micro- and nanostructures controlled by external stimuli remains one of the exciting challenges in nanotechnology due to the wealth of fundamental questions and potential applications in energy harvesting, robotics, sensing, biomedicine, and tunable metamaterials. Photoactuation utilizes the conversion of light into motion through reversible chemical and physical processes and enables remote and spatiotemporal control of the actuation. Here, we report a fast light-to-motion conversion in few-nanometer thick bare polydopamine (PDA) membranes stimulated by visible light. Light-induced heating of PDA leads to desorption of water molecules and contraction of membranes in less than 140 μs. Switching off the light leads to a spontaneous expansion in less than 20 ms due to heat dissipation and water adsorption. Our findings demonstrate that pristine PDA membranes are multiresponsive materials that can be harnessed as robust building blocks for soft, micro-, and nanoscale actuators stimulated by light, temperature, and moisture level.
Highlights
A skeletal muscle tissue, which has been optimized over hundreds of millions of years of evolution, represents the role model for the design and synthesis of soft materials serving as artificial muscles and actuators
Movie of PDA membrane subjected to uniform heating (MP4)
Corresponding Authors Tanja Weil − Max Planck Institute for Polymer Research, we demonstrated for the first time fast photoactuation
Summary
A skeletal muscle tissue, which has been optimized over hundreds of millions of years of evolution, represents the role model for the design and synthesis of soft materials serving as artificial muscles and actuators. The membrane contracts and flattens when exposed to high-power laser irradiation (red laser ON, central panel of Figure 3a) This behavior results in specular reflection of the green laser light captured by the photodiode. Prior studies showed that the Young modulus of PDA significantly increases with heating.[45] the observed reduction of v in Figure 4c,d can be explained by membrane contraction, which corroborates with the results of optical microscopy. Additional information on the (i) preparation and characterization of the PDA membranes (cyclic voltammetry, grazing incidence angle FTIR, and atomic force microscopy), (ii) optical properties of the membranes, (iii) damage threshold for laser irradiation, (iv) processing of the time-resolved reflectivity data, and (v) sum-frequency-generation spectroscopy measurements and their analysis, (vi) reflectivity dynamics of larger membranes (PDF). The temperature at which the membranes become flat (i.e., 370 K in Figure 2b and 333−343 K in Figure 4a) match the temperature for desorption of surface-bound water from PDA (340−350 K).[28,51]
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