Redefining the limits of actuating fibers via mesophase control: From contraction to elongation.

The development of fibrous actuators with diverse actuation modes is expected to accelerate progress in active textiles, robotics, wearable electronics, and haptics. Despite the advances in responsive polymer-based actuating fibers, the available actuation modes are limited by the exclusive reliance of current technologies on thermotropic contraction along the fiber axis. To address this gap, the present study describes a reversible and spontaneous thermotropic elongation (~30%) in liquid crystal elastomer fibers produced via ultraviolet-assisted melt spinning. This elongation arises from the orthogonal alignment of smectogenic mesogens relative to the fiber axis, which contrasts the parallel alignment typically observed in nematic liquid crystal elastomer fibers and is achieved through mesophase control during extrusion. The fibers exhibiting thermotropic elongation enable active textiles increase pore size in response to temperature increase. The integration of contracting and elongating fibers within a single textile enables spatially distinct actuation, paving the way for innovations in smart clothing and fiber/textile actuators.