Smart materials including liquid crystal elastomers (LCE) and shape memory polymers (SMP) have long been used as the primary components of multifunctional composites because of their shape and property changes in response to external stimuli. However, LCEs can generate rapid and reversible shape changes but are soft and require a constant temperature to retain their deformed shape; SMPs have favorable mechanical properties but few can achieve reversible actuations. Moreover, both LCEs and SMPs have limited capability for tunable shape morphing. In this work, Qi and his collaborators develop a 4D printed composite comprised of an LCE and an SMP which can achieve not only large, rapid, reversible shape changes but also tunable shape changes while maintaining a mechanical stiffness of ~1GPa in the actuated state. To achieve tunability, the authors harness the distinct time-dependent thermo-mechanical properties of the LCE and SMP, whose shape-changing characteristics are highly dependent on the cooling rate, to control the overall shape-changing behavior of the composite, i.e. with different cooling rates, the composite can morph into different shapes with high stiffness at low temperatures. A multi-material 4D printing approach is then utilized to fabricate an LCE-SMP bilayer composite wherein the SMP and the LCE are printed by digital light processing (DLP) and DIW printing, respectively. Multiple LCE-SMP composites are then designed and fabricated to demonstrate the unique advantages of high mechanical stiffness and tunable shape morphing behaviors. Using this new approach, novel applications for 4D printed multifunctional composites may be discovered for future use in space, biomedicine, and energy technologies.
This work was conducted by Prof. H. Jerry Qi’s group at Georgia Tech in collaboration with Prof. Frédéric Demoly of University Bourgogne Franche-Comté, and Prof. Kun Zhou of Nanyang Technological University. Dr. Devin Roach, Dr. Xiaohao Sun, and Mr. Xirui Peng contributed equally to this work.
Further information on this work could be found in the recently published article in the following link:
https://doi.org/10.1002/adfm.202203236
Roach, Devin J., Xiaohao Sun, Xirui Peng, Frédéric Demoly, Kun Zhou, and Hang Jerry Qi. “4D Printed Multifunctional Composites with Cooling‐Rate Mediated Tunable Shape Morphing.” Advanced Functional Materials (2022): 2203236.