• Energy Research

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.

Modifying bitumens to improve their characteristics is one of the ways to increase road pavement durability reducing maintenance costs and environmental issues. In this study the structural and mechanical characteristics of a 50/70 bitumen modified by two different char samples are presented. The choice of char as bitumen modifier fulfils the recent needs for environmental protection. The two char samples come from the pyrolysis of Refuse Derived Fuel (RDF) and waste tyres (WT), respectively. They differ in composition and morphology and their production took place with different yields. Char-modified bitumens revealed increased shear modulus and resistance to mechanical stress as found by rheometry. Artificial aging of these char-modified bitumens unveiled that the bitumen modified by char from WT (WT-char) possessed a certain resilience against aging, with a reduced increase in rigidity upon aging. The anti-aging effect showed by WT-char was attributed to its higher carbon content, which confers higher compatibility with the bitumen chemical nature and presumably a more uniform dispersion within the bituminous structure thanks to the establishment of more effective interactions.