Transparent PDMS Surfaces with Covalently Attached Lubricants for Enhanced Anti-adhesion Performance

Liquid-like surfaces featuring slippery, omniphobic, covalently attached liquids (SOCALs) reduce unwanted adhesion by providing a molecularly smooth and slippery surface arising from the high mobility of the liquid chains. Such SOCALs are commonly prepared on hard substrates, such as glass, wafers, or metal oxides, despite the importance of nonpolar elastomeric substrates, such as polydimethylsiloxane (PDMS) in anti-fouling or nonstick applications. Compared to polar elastomers, hydrophobic PDMS elastomer activation and covalent functionalization are significantly more challenging, as PDMS tends to display fast hydrophobic recovery upon activation as well as superficial cracking. Through the extraction of excess PDMS oligomers and fine-tuning of plasma activation parameters, homogeneously functionalized PDMS with fluorinated polysiloxane brushes could be obtained while at the same time reducing crack formation. Polymer brush mobility was increased through the addition of a smaller molecular silane linker to exhibit enhanced dewetting properties and reduced substrate swelling compared to functionalizations featuring hydrocarbon functionalities. Linear polymer brushes were verified by thermogravimetric analysis. The optical properties of PDMS remained unaffected by the activation in high-frequency plasma but were impacted by low-frequency plasma. Drastic decreases in solid adhesion of not just complex contaminants but even ice could be shown in horizontal push tests, demonstrating the potential of SOCAL-functionalized PDMS surfaces for improved nonstick applications.

Mini-Review on Bioinspired Superwetting Microlens Array and Compound Eye

Microlens arrays (MLAs) and MLA-based artificial compound eyes (ACEs) are the important miniaturized optical components in modern micro-optical systems. However, their optical performance will seriously decline once they are wetted by water droplets (such as fog, dew, and rain droplets) or are polluted by contaminations in a humid environment. In this mini-review, we summarize the research works related to the fabrication of superwetting MLAs and ACEs and show how to integrate superhydrophobic and superoleophobic microstructures with an MLA. The fabrication strategy can be split into two categories. One is the hybrid pattern composed of the MLA domain and the superwetting domain. Another is the direct formation of superwetting nanostructures on the surface of the microlenses. The superhydrophobicity or superoleophobicity endows the MLAs and ACEs with liquid repellence and self-cleaning function besides excellent optical performance. We believe that the superwetting MLAs and ACEs will have significant applications in various optical systems that are often used in the humid or liquid environment.

An Aqueous Composition for Lubricant-Free, Robust, Slippery, Transparent Coatings on Diverse Substrates

Transparent, durable coating materials that show excellent liquid repellency, both water and oil, have multiple applications in science and technology. In this perspective, herein, a simple aqueous chemical formulation is developed that provides a transparent slippery coating without any lubricating fluids, on various substrates extended over large areas. The coatings repel liquids having a range of polarity (solvents) as well as viscosity (oils and emulsions) and withstand mechanical strains. Exceptional optical transparency of 99% in the range of 350-900 nm along with high stability even after cyclic temperature, frost, exposure to sunlight, and corrosive liquids like aqua regia treatments, makes this material unique and widens its applicability in different fields. Besides, being a liquid, it can be coated on an array of substrates independent of their underlying topography, by various easily available techniques. Aside from these interesting properties, the coating is demonstrated as a potential solution contributing to the remediation of one of the biggest global issues of tomorrow: affordable drinking water. The coated surface can capture 5 L of water per day per m2 at 27 °C when exposed to an atmosphere of 63% relative humidity.