Megha Emerse | Searcharxiv

arXiv2026

Resolving Light-Induced Structural Rearrangements in Responsive Microgels

Optically-responsive microgels offer a versatile platform for designing adaptive soft materials with coupled light and thermal responsiveness. Control over the crosslinking degree is particularly appealing as it can regulate not only particle size but also stiffness, thereby enabling remote tuning of key material functionalities. However, the internal structural changes that couple molecular photoresponsive mechanisms to mesoscopic properties remain poorly resolved. Here, we investigate different light-responsive microgels containing covalently incorporated coumarin moieties, which impart optical sensitivity through UV-induced cycloaddition, by combining dynamic light scattering, small-angle neutron scattering, and molecular dynamics simulations. We show that light irradiation alters not only particle size but also the internal polymer density distribution and subsequent thermal response. Before irradiation, the microgels exhibit a star-like architecture with a dense core and extended polymeric arms. After irradiation, the network evolves toward a markedly more compact structure. This transformation cannot be rationalized simply as an equivalent to an increase in crosslinking density during synthesis, as observed in the thermal response, revealing light as a powerful tool to regulate microgel architecture and multifunctional responsiveness.

cond-mat.soft↗

arXiv2024

Wrinkling and imaging of thin curved sheets

Thin films or sheets subjected to external forces often undergo mechanical instability, leading to regular patterns of wrinkles, folds, and creases. As can be anticipated from the difficulty of flattening a curved globe, any natural curvature of the sheet will have a strong influence on these instabilities. Here, we develop a non-invasive synthetic schlieren imaging technique to image and reconstruct the surface of wrinkling curved sheets, confined to float on water. Our method circumvents the small-amplitude limit of related imaging techniques, and we demonstrate robust means to estimate the reconstruction accuracy. We then evaluate how the sign and magnitude of Gaussian curvature affects the wrinkling of thin curved sheets, and compare observations of the wrinkle wavelength, amplitude and domain structure with recent theoretical predictions. While generally validating model predictions, we find that the assumption of a conserved surface area during wrinkling should be treated with some care. The control of wrinkling behavior demonstrated here can have application in the design of liquid lenses, microfluidics, active textured surfaces, and flexible electronic components.

nlin.PS↗