Abstract
Fibrous liquid crystalline elastomers (LCE) are an attractive variant of LCE-based actuators due to their small thickness, leading to faster response times to stimuli, as well as the increased mechanical strength. Fabrication of LCE fibers has been attempted by various research groups using electro-spinning or micro-fluidic techniques, without much success. Here we propose an alternative way to achieve single-step continuous spinning LCE fibers in a more scalable and robust way, based on a liquid-ink 3D printer. We demonstrate this technique in our home-made device by dynamically extruding/stretching liquid crystalline oligomer mixed with photo-reactive cross-linker, to fix the aligned network under UV light after extrusion. The report also describes a protocol for material synthesis and identifies optimal conditions for the stable fiber spinning process. Microns-thick LCE fibers with two different compositions have been successfully spun, and demonstrated enhanced mechanical properties with the inherited thermal-actuation capability. This technique also demonstrates the potential to fine-tune the mechanical properties of fibers to enable further development in fiber-based LCE applications.
Highlights
Liquid crystalline elastomers (LCE) represent a unique type of soft material
After the fiber spinning process, the thiolcapped nematic oligomers were radically crosslinked with vinyl siloxane crosslinker, (TVCS) and vinyl siloxane spacer, (DVS) by photo-initiated reaction to produce xLCE fiber with the dynamic polymer network topology
We described the detailed steps in the synthesis and the fiber spinning process, and highlighted key precautions
Summary
Liquid crystalline elastomers (LCE) represent a unique type of soft material One of their key features is that when manufactured in an aligned mono-domain state, they are capable of achieving large, reversible length changes, reflecting the equilibrium relation between the macroscopic shape of the soft solid and the internal degree of orientational order.[1] Since the first development of LCEs in laboratory over 30 years ago,[2] the two-step cross-linking process remains a standard fabrication scheme to produce mono-domain, aligned ‘single-crystal’ LCE.[3] This process typically requires manual mechanical stretching of the initially loosely cross-linked LC gel, followed by the secondary cross-linking that fixes the induced orientational order, as well as sample shape. Currently most known methods apart from mechanical stretching, such as electromagnetic field[4] and surface alignment[5,6] are yet to solve the problem
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