Perspiring Soft Robotics Skin Constituted by Dynamic Polarity-Switching Porous Liquid Crystal Membrane.

Secretion of functional fluids is essential for affecting surface properties, such as lubrication, and transporting biochemical elements in ecosystems [ 2 ] . The existing synthetic polymer membranes that mimic human skin functions are primarily limited to secreting, either apolar or polar, liquid [ 4 ] . However, the development of membranes that grant exchange liquid with different polarities with the capability to subsequently eject it again remains a grand challenge. This process is fundamentally prohibited by the mismatch of the polarity between the carrier polymer and the loaded liquid. To conquer this physical limitation, we report an innovative strategy to dynamically switch the polarity of the porous membrane skin, thereby empowering exchange apolar liquid with polar liquid and vice versa. Our approach incorporates a benzoic acid derivative into the original apolar polymer network. The benzoic acid dimerizes and forms hydrogen bonds, which supports the processing procedure and molecular alignment, but can be broken into the ionic state when subjected to alkaline treatment, changing the polarity of the polymer membrane. Consequently, the apolar liquid can be replaced with a more polar one. This polar liquid is ejected upon safe-dose UV illumination from the polymer membrane. Reabsorption may occur on demand by illumination of visible light or, when left in contact with the membrane, spontaneously in the dark. Based on this, the consumed membrane is replenished with the same or different exchanging liquid. The membrane's ability to secrete, uptake, and exchange versatile liquids, even at two extremes of the spectrum, broadens the application fields of the membrane ranging from lubrication, anti-icing, to drug delivery. We envision that the polarity-switching active membrane skins will open up an avenue for, among others, soft robotics [ 6 ] , lithium-ion batteries [ 7 ] , environment-interactive surfaces [ 8 ] , and biomedical science and technology [ 9 ] . This article is protected by copyright. All rights reserved.