Abstract
AbstractSmart surfaces that reversibly change the interfacial friction coefficients in response to external stimuli enable a wide range of applications, such as grips, seals, brake pads, packaging films, and fabrics. Here, a new concept of such a smart frictional system is reported: a composite film of a plain‐weave polyester textile sheet and a thermoresponsive nematic liquid crystalline elastomer (LCE). The composite is deployed with retractable microundulations of the elastomer inside each weave mesh, enabling dramatic changes of the contact interface with the opposing surface on LCE actuation, which is induced, e.g., by a change in temperature (T). At room T, the protruding viscoelastic parts of LCE in the nematic phase make contact with the opposing flat surface, resulting in a very high friction. At an elevated T (≈50 °C, isotropic phase), the undulations of LCE surface are retracted within the thickness of the textile, and the contacts are limited to small regions around overlapping textile fibers, lowering the friction dramatically. This effect is fully reversible on heating/cooling cycles. The surface undulations are spontaneous, i.e., fabricated without any lithographic or alignment techniques. The present composite opens a new way for the application of sheets/films with switchable friction enabled by stimuli‐responsive LCEs.
Highlights
The parameters controlling friction can be reviewed by considering a model for the dry friction in polymers and elastomers, which is known as the ‘adhesive friction model’[2,3,12]
The friction force arises from the shear strength to open the contact interface
Liquid crystal elastomers (LCEs) are very promising systems to induce very large topographical changes via phase transitions[17,18,19,20,21,22,23,24,25] that can be triggered by multiple stimuli, such as temperature, light, and chemicals
Summary
The parameters controlling friction can be reviewed by considering a model for the dry friction in polymers and elastomers, which is known as the ‘adhesive friction model’[2,3,12]. The proposed changes become possible through a fine geometrical design of thermally retractable micro-undulations of LCE ‘pockets’ formed in each opening of the textile mesh. At room temperature (RT), the buckled viscoelastic LCE parts in the nematic phase protrude out of the composite film and make contact with the opposing surface over a large area, resulting in high friction.
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