Dewdrop Metasurfaces and Dynamic Control Based on Condensation and Evaporation.

Dewdrops, the droplets of water naturally occurring on leaves and carapaces of insects, are a fascinating phenomenon in nature. Here, a man-made array of dewdrops with arbitrary shapes and arrangements, which can function as an electromagnetic metasurface, is demonstrated. The realization of the dewdrop array is enabled by a surface covered by a tailored pattern of hydrophilic and hydrophobic coatings, where tiny droplets of water can aggregate and form dewdrops on the former. Interestingly, this metasurface made of dewdrops can be modulated by the condensation and evaporation process. By increasing relative humidity and decreasing temperature, the dewdrop metasurface is gradually formed with increasing amounts of water. While the reverse operation can make it completely disappear. This idea is demonstrated through two examples with different functions of dynamically controllable microwave absorption and scattering. The work shows a principle to construct functional electromagnetic devices with dewdrops, as well as a mechanism of dynamic control based on condensation and evaporation, promising unprecedented applications.

Ascorbic acid-mediated reduction of arabinoxylan viscosity through free radical reactions.

Arabinoxylan (AX) is a potential natural food additive that can enhance the textural properties of food. However, the addition of ascorbic acid (AA) can easily lead to a decrease in the viscosity of AX, which poses a challenge in the development of AX-rich foods. Therefore, the purpose of this study is to elucidate the mechanisms behind the reduction in AX viscosity in the presence of AA. The results indicated that AA could reduce the apparent viscosity and molecular weight of AX without significantly affecting the monosaccharide composition, suggesting a potential mechanism related to the cleavage of AX glycosidic bonds. Interestingly, free radicals were present in the reaction system, and the generation of free radicals under different conditions was consistent with the reduction in apparent viscosity of AX. Furthermore, the reduction in AX apparent viscosity by AA was influenced by various factors including AA concentration, reaction time, temperature, pH, and metal ions. These findings suggested that the mechanism of AX degradation may be due to AA-induced free radical generation, leading to non-selective attacks on glycosidic bonds. Therefore, this study revealed that the potential mechanism behind the reduction in AX viscosity induced by AA involved the generation of ascorbic acid radicals.

Matte surfaces with broadband transparency enabled by highly asymmetric diffusion of white light.

The long-standing paradox between matte appearance and transparency has deprived traditional matte materials of optical transparency. Here, we present a solution to this centuries-old optical conundrum by harnessing the potential of disordered optical metasurfaces. Through the construction of a random array of meta-atoms tailored in asymmetric backgrounds, we have created transparent matte surfaces that maintain clear transparency regardless of the strength of disordered light scattering or their matte appearances. This remarkable property originates in the achievement of highly asymmetric light diffusion, exhibiting substantial diffusion in reflection and negligible diffusion in transmission across the entire visible spectrum. By fabricating macroscopic samples of such metasurfaces through industrial lithography, we have experimentally demonstrated transparent windows camouflaged as traditional matte materials, as well as transparent displays with high clarity, full color, and one-way visibility. Our work introduces an unprecedented frontier of transparent matte materials in optics, offering unprecedented opportunities and applications.