Stimuli-responsive surfaces for switchable wettability and adhesion

Abstract

Diverse unique surfaces exist in nature, e.g. lotus leaf, rose petal and rice leaf. They show similar contact angles but different adhesion properties. According to the different wettability and adhesion characteristics, this review reclassifies different contact states of droplets on surfaces. Inspired by the biological surfaces, smart artificial surfaces have been developed which respond to external stimuli and consequently switch between different states. Responsive surfaces driven by various stimuli, e.g. stretching, magnetic, photo, electric, temperature, humidity and pH, are discussed. Studies reporting on either atmospheric or underwater environments are discussed. The application of tailoring surface wettability and adhesion includes microfluidics/droplet manipulation, liquid transport and harvesting, water energy harvesting and flexible smart devices. Particular attention is placed on the horizontal comparison of smart surfaces with the same stimuli. Finally, the current challenges and future prospects in this field are also identified.

Role of chemistry in bio-inspired liquid wettability

“…Thermosensitive chemical functionalities have the ability to change its surface topography or chemistry in response to temperature acting as an external stimuli. 239 Poly( N -isopropylacrylamide) (PNIPAAm) is a well-known thermoresponsive polymer. 240 At temperatures below the lower critical solution temperature (LCST), PNIPAAm polymer chains form intermolecular hydrogen bonds with water molecules, whereas at temperatures above LCST, PNIPAAm chains change their conformation to form intramolecular hydrogen bonds and the non-polar moieties are exposed toward the surface, which leads to a decrease in the surface energy.…”

A New Reversible Thermosensitive Liquid–Solid TENG Based on a P(NIPAM‐MMA) Copolymer for Triboelectricity Regulation and Temperature Monitoring

“…[32] The LCST phenomenon of PNIPAM is mainly caused by the conformational transition of hydrophilic amide group (CONH) and hydrophobic isopropyl group (CH(CH 3 ) 2 ) inside it. [33,34] Below the LCST, amide group of PNIPAM provides a hydrogen bond donor to form hydrogen bonds with the surrounding water molecules, resulting in a fully hydrated extended state. When the temperature rises above the LCST, the amide group tends to be enveloped by the nonpolar main chain, and PNIPAM is in its shrinking state.…”

Robust Underwater Oil-Repellent Biomimetic Ceramic Surfaces: Combining the Stability and Reproducibility of Functional Structures

“…In marine ecosystems, oil pollution caused by industrial accidental oil spills, manufacuturing, and scientific exploration has become increasingly serious. , Meanwhile, human activity in these oil-contaminated waters is increasingly frequent. Therefore, researchers and engineers are continuously looking for new tough, superoleophobic materials exhibiting low oil adhesion underwater. − In recent years, biomimetic surfaces with layered micro/nanoprotrusions and high surface energies have been proposed as a means to provide outstanding underwater superoleophobic performance. − Their designs are inspired by natural examples such as shark skin, shell nacre, − seaweed, etc. They are built with materials such as oxides, − polyelectrolytes, − or polymer hydrogels. , Although these surfaces have unique superoleophobic properties in water, many of the metal oxides (i.e.…”

“…or top-down (laser etching, chemical etching, etc. ), place the functionality of the material on the surface. , Once the structure of the surface layer wears down, the entire material loses its function. Therefore, we need to develop a new approach so that the surface structure can regenerate even if it is destroyed.…”