Dynamic self-stiffening in liquid crystal elastomers

Abstract

Biological tissues have the remarkable ability to remodel and repair in response to disease, injury, and mechanical stresses. Synthetic materials lack the complexity of biological tissues, and man-made materials which respond to external stresses through a permanent increase in stiffness are uncommon. Here, we report that polydomain nematic liquid crystal elastomers increase in stiffness by up to 90% when subjected to a low-amplitude (5%), repetitive (dynamic) compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Through rheological and X-ray diffraction measurements, stiffening can be attributed to a nematic director which rotates in response to dynamic compression. Stiffening under dynamic compression has not been previously observed in liquid crystal elastomers and may be useful for the development of self-healing materials or for the development of biocompatible, adaptive materials for tissue replacement.

Stepped Moduli in Layered Composites

“…[20,21] Mechanical stress can also serve as a stimulus to change mechanical properties of materials. Liquid crystals [22] or carbon nanotubes [23] embedded in elastomers show a permanent self-stiffening response when subjected to recurring elastic stress; this response is superficially similar (although based on an entirely different mechanism) to the adaptive strengthening of bones that improves their strength due to repeated mechanical loading. [24] A few crystalline solids (Fe 3 C and Al 3 BC 3 ) [25] and physically-associating synthetic polymer networks [26,27] also change their mechanical strength in response to mechanical stimuli.…”

Liquid crystals: applications and industry

“…The effect is somewhat analogous to the adaptive material behaviours found in biology, and indeed the researchers hope this could be useful in producing bionic materials [5,6].…”

Thermally and Optically Fixable Shape Memory in Azobenzene-Functionalized Glassy Liquid Crystalline Polymer Networks

“…The mechanical adaptivity of LCNs has garnered considerable recent attention for potential relevance in microfluidics [18], optics [19,20], structural mechanics [17,21,22], and medicine [23,24]. One of the salient features of LCN materials versus other stimuliresponsive polymers [25][26][27][28][29][30] is the ability to easily control the local director [2,[31][32][33][34] or defect [35][36][37][38][39] pattern within the film.…”