External Stimuli Responsive Liquid‐Infused Surfaces Switching between Slippery and Nonslippery States: Fabrications and Applications

Abstract

Surfaces with controllable liquid wettability and related functions have gained increasing attention from interfacial scientists due to the high demand of fundamental research and practical applications. Inspired by pitch plant's excellent liquid repellency, external stimuli responsive lubricant‐infused surfaces switching between slippery state and nonslippery state under external stimuli (E‐LIS) have been developed by introducing external stimuli responsive materials as substrates, lubricants, or repellent liquids. This progress report is focused on recent development of E‐LIS. First, design strategy and fabrication of E‐LIS upon external stimuli exposure, including stress, electrical field, magnetic field, and temperature, is summarized. Then, emerging interfacial applications of E‐LIS, such as microreactors, pipetting devices, fog collection devices, and so on, are highlighted. In addition, remaining challenges and future prospects are provided.

Factors controlling the pinning force of liquid droplets on liquid infused surfaces

“…This is due to the fact that increasing g lg generally makes a droplet on LIS to be more hydrophilic-like, while increasing g ld makes it more hydrophobic-like, and thus the change of the contact angles follow accordingly. 33,34 Finally, we have argued in eqn (15) and (16) that the pinning force of a droplet on LIS does not depend on the droplet-gas interfacial tension g dg . Indeed, while the magnitudes of the advancing and receding angles are influenced by g dg , see Fig.…”

“…One important observation from eqn (15) or eqn (16) is that the magnitude of the pinning force does not actually depend on the droplet-gas surface tension, g dg , which distinguishes the case of pinning on LIS to pinning on other solid surfaces. Additionally, eqn (16) highlights that there is no pinning for the complete lubricant wetting case (y lg = y ld = 01).…”

“…Additionally, eqn (16) highlights that there is no pinning for the complete lubricant wetting case (y lg = y ld = 01). Nonetheless, to allow comparisons with other solid surfaces, it is useful to write eqn (15) in the following form…”

“…[10][11][12][13][14] On the other hand, LIS with partially wetting lubricant have increasingly attracted interest, especially with a number of external stimuli shown to allow reversible change of wetting states from slippery to sticky (see for example the recent review ref. 15). Such surfaces have substantially expanded functionality compared to the purely slippery surfaces, with the ability to locally change a droplets' mobility leading to the demonstration of fog capture even in high winds, 16 to introduce bidirectional motion under texture gradients, 17 and recently the unprecedented manipulation of both droplets and colloids.…”

Bioinspired superwetting surfaces for biosensing

“…Three principles have been put forward to designing SLIPS. [80][81] The first one is that the selected lubricating liquid must wick into, wet, and stably adhere to the substrate. In regard to the second one, the lubricating liquid should wet the solid surface to form a stable liquid layer.…”