Development of poly(l-Lactic Acid)-based bending actuators

This work reports on the development of bending actuators based on poly(l-lactic acid) (PLLA)/ionic liquid (IL) blends, through the incorporation of 40% wt. of the 1-ethyl-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Emim][TFSI]) IL. The films, obtained by solvent casting at room temperature and 50 °C, were subjected to several post-thermal treatments at 70, 90, 120 and 140 °C, in order to modify the crystallinity of the films. The influence of the drying temperature and of [Emim][TFSI] blending on the morphological, structural, mechanical and electrical properties of the composite materials were studied. The IL induced the formation of a porous surface independently of the processing conditions. Moreover, the [Emim][TFSI] dopant and the post-thermal treatments at 70 °C promoted an increase of the degree of crystallinity of the samples. No significant changes were observed in the degree of crystallinity and Young Modulus for samples with thermal treatment between 70 and 140 °C. The viability of the developed high ionic conductive blends for applications as soft actuators was evaluated. A maximum displacement of 1.7 mm was achieved with the PLLA/[Emim][TFSI] composite prepared at 50 °C and thermally treated at 140 °C, for an applied voltage of 10 Vpp, at a frequency of 100 mHz. This work highlights interesting avenues for the use of PLLA in the field of actuators.The authors thank the FCT—Fundação para a Ciência e Tecnologia—for financial support under the Strategic Funding UID/FIS/04650/2020, and PEST-C/QUI/UIO686/2019, the Associated Laboratory Research Unit for Green Chemistry, Technologies and Clean Processes, LAQV (financed by national funds from FCT/MEC, UID/QUI/50006/2020 and ERDF under the PT2020, POCI-01-0145-FEDER-007265) and projects PTDC/BTM-MAT/28237/2017 and PTDC/EMD-EMD/28159/2017. DMC and LCF also thank the grants SFRH/BPD/121526/2016 and SFRH/BD/145345/2019, respectively