Additive Manufacturing of Liquid Crystal Elastomers
3D printing revolutionized manufacturing, and now researchers are setting their sights on four-dimensional (4D) printing, a term that describes the additive manufacturing of stimuli-responsive materials that morph into distinct 3D geometries over time. These commutable structures may enable an unprecedented variety of smart devices such as soft robots or morphing medical devices, but requires fine control over material microstructures in order to influence macroscopic deformations. For example, controlling the local coefficient of thermal expansion in printed structures can create objects with a negative global coefficient of thermal expansion that contract, rather than expand, while heating. However, this deformation is limited in size and is isotropic in nature. Direct-write printing (or extrusion printing) can be used to create hydrogels that locally swell in a single direction, which can be utilized to create structures that deform on a macro scale, but hydrogel shape change is limited by diffusion speed and the requisite aqueous environment. In order to truly achieve 4D smart systems, it would be necessary to create printable materials that can undergo large, anisotropic, rapid, and reversible deformations.
Description
Liquid crystal elastomers (LCEs) are mechanically-active, stimuli-responsive soft polymers that undergo large, reversible, anisotropic shape change in response to a variety of stimuli, including heat and light. These materials require neither an external load nor an aqueous environment to undergo this change. By controlling molecular orientation using shear forces, LCE shape change can be patterned spatially and hierarchically. Direct-write printing can then be used to print structures capable of being triggered to morph from one state to another. This is a scalable technique that produces 3D structures capable of reversible, untethered, and low-hysteresis shape change, enabling 4D printed materials to operate as autonomous morphing structures capable of reacting to stimuli.Applications
· Transducing thermal, chemical, magnetic, or light energy into mechanical work· Soft robots
· Morphing medical devices, such as artificial muscles
· Sensors
· Aerospace systems
Advantages
· Provides increased molecular control for better programming of desired outcome· Scalable technique can be implemented for applications at all scales
· Shape change is comparably large
· Rapid deformation is a significant improvement over 3D printed hydrogels; transitions can occur on the scale of milliseconds
· Deformations at the macroscale are reversible
· Shape change does not require a tethered power source or an aqueous environment