Hydrochannel-Containing Hydrophobic Polymers by Inverse Emulsion Polymerization for Moisture-Driven Actuators

Superhydrophobic and highly moisture-resistant PVA@EC composite membrane for air purification

Electrospun fiber membranes have great potential in the field of air filtration because of their high porosity and small pore size. Conventional air filtration membranes are hydrophilic, leading to weak moisture-barrier properties, which hinders their application in high-humidity environments. In this study, eugenol was added to polyvinyl alcohol and ethyl cellulose (EC) for electrospinning and electrospraying, respectively, of superhydrophobic bilayer composite fiber membranes to efficiently filter particulate matter (PM) in air. Owing to its surface microstructure, electrosprayed EC increased the water contact angle of the PVA membrane from 142.8 to 151.1°. More importantly, the composite air-filter membrane showed a low filtration pressure drop (168.1 Pa) and exhibited high filtration efficiencies of 99.74 and 99.77% for PM1.0 and PM2.5, respectively, and their respective quality factors were 0.0351 and 0.0358 Pa-1. At the same time, the filtration performance of the air filtration membrane remained above 99% at high air humidity. This work reports composite membranes that can effectively capture PM of various sizes and thus may provide a reference for the manufacturing of green air filters for high-humidity environments.

Robust Hydrophobic Materials by Surface Modification in Transition-Metal Diborides

Exploring the hydrophobicity of robust conductors is significant for electronic devices to simultaneously be used in a wet environment and extreme conditions. However, a combination of conductivity, strong mechanical properties, and hydrophobicity in one material is hindered by the inherent features of the materials. A new kind of robust hydrophobic conductor is designed in transition-metal diborides (TMdBs: TiB₂, ZrB₂, and HfB₂) to break through this challenge. The results calculated by density functional theory indicate that high hardness comes from high shear and bulk modulus, which is consistent with experimental results (TiB₂, 25.0 GPa; ZrB₂, 17.5 GPa; HfB₂, 21.5 GPa). The theoretical calculated results reveal that edge sides have a lower surface energy than basal plane (001) in TMdBs. Hence, the edge sides are exposed with a needle-like morphology in TMdBs. Moreover, needle-like surfaces exhibiting hydrophobicity have water contact angles of 132.0° (TiB₂), 116.8° (ZrB₂), and 114.0° (HfB₂). The hydrophobicity arises from a lower surface free energy of edge sides in TMdBs and a rough surface that reduces the contact area of water and a solid. This work develops a new kind of robust functional material in TMdBs.

Highly Sunlight Reflective and Infrared Semi-Transparent Nanomesh Textiles

Radiative cooling in textiles is one of the important factors enabling cooling of the human body for thermal comfort. In particular, under an intense sunlight environment such as that experienced with outdoor exercise and sports activities, high near-infrared (NIR) reflectance to block sunlight energy influx along with high IR transmittance in textiles for substantial thermal emission from the human body would be highly desirable. This investigation demonstrates that a nanoscale geometric control of textile structure alone, instead of complicated introduction of specialty polymer materials and composites, can enable such desirable NIR and IR optical properties in textiles. A diameter-dependent Mie scattering event in fibers and associated optical and thermal behavior were simulated in relation to a nonwoven, nanomesh textile. As an example, a nanomesh structure made of PVDF (polyvinylidene fluoride) electrospun fibers with ∼600 nm average diameter was examined, which exhibited a significant radiative cooling performance with over 90% solar and NIR reflectance to profoundly block the sunlight energy influx as well as ∼50% IR transmittance for human body radiative heat dissipation. An extraordinary cooling effect, as much as 12 °C, was obtained on a simulated skin compared to the normal textile fabric materials. Such a powerful radiative cooling performance together with IR transmitting capability by the nanomesh textile offers a way to efficiently manage sunlight radiation energy to make persons, devices, and transport vehicles cooler and help to save energy in an outdoor sunlight environment as well as indoor conditions.