Influence of cellulose nanocrystal surface functionalization on the bending response of cellulose nanocrystal/ionic liquid soft actuators.

This work reports the development of renewable cellulose nanocrystal (CNC) and ionic liquid (IL) hybrid materials for bending actuator applications. For this purpose, cellulose nanocrystals with different surface charges (neutral, positive and negative) were prepared and increasing amounts of the IL 2-hydroxy-ethyl-trimethylammonium dihydrogen phosphate ([Ch][DHP]) (10 and 25 wt%) were incorporated into the CNC hosting matrix. The morphology of the samples was evaluated, proving that both surface charge and IL incorporation do not affect the characteristic layered structure of the CNC. Atomic force microscopy results reveal a sea-island morphology in the hybrid films, where CNC bundles are surrounded by [Ch][DHP]-rich regions. An increase in the electrical conductivity is observed upon IL incorporation into the CNC matrix, regardless of the CNC surface charge. The highest electrical conductivity values are observed for IL/CNC (+) 25 wt% with an electrical conductivity of 3.18 × 10-5± 2.75 × 10-7 S cm-1 and IL/CNC (-) 10 wt% (1.26 × 10-5± 5.92 × 10-6 S cm-1). The highest bending displacement of 2.1 mm for an applied voltage of 4.0 Vpp at a frequency of 100 mHz was obtained for the IL/CNC (+) 25 wt% composite, demonstrating the suitability of cellulose to develop soft actuators.

Multifunctional Magnetoelectric Sensing and Bending Actuator Response of Polymer-Based Hybrid Materials with Magnetic Ionic Liquids.

With the evolution of the digital society, the demand for miniaturized multifunctional devices has been increasing, particularly for sensors and actuators. These technological translators allow successful interaction between the physical and digital worlds. In particular, the development of smart materials with magnetoelectric (ME) properties, capable of wirelessly generating electrical signals in response to external magnetic fields, represents a suitable approach for the development of magnetic field sensors and actuators due to their ME coupling, flexibility, robustness and easy fabrication, compatible with additive manufacturing technologies. This work demonstrates the suitability of magnetoelectric (ME) responsive materials based on the magnetic ionic liquid (MIL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]) and the polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) for magnetic sensing and actuation device development. The developed sensor works in the AC magnetic field and has frequency-dependent sensitivity. The materials show voltage responses in the mV range, suitable for the development of magnetic field sensors with a highest sensitivity (s) of 76 mV·Oe-1. The high ME response (maximum ME voltage coefficient of 15 V·cm-1·Oe-1) and magnetic bending actuation (2.1 mm) capability are explained by the magnetoionic (MI) interaction and the morphology of the composites.

Electrospun Magnetic Ionic Liquid Based Electroactive Materials for Tissue Engineering Applications.

Functional electrospun fibers incorporating ionic liquids (ILs) present a novel approach in the development of active microenviroments due to their ability to respond to external magnetic fields without the addition of magnetic particles. In this context, this work reports on the development of magnetically responsive magneto-ionic fibers based on the electroactive polymer poly(vinylidene fluoride) and the magnetic IL (MIL), bis(1-butyl-3-methylimidazolium) tetrathiocyanatocobaltate ([Bmim]2[(SCN)4Co]). The PVDF/MIL electrospun fibers were prepared incorporating 5, 10 and 15 wt.% of the MIL, showing that the inclusion of the MIL increases the polar ß-phase content of the polymer from 79% to 94% and decreases the crystallinity of the fibers from 47% to 36%. Furthermore, the thermal stability of the fibers decreases with the incorporation of the MIL. The magnetization of the PVDF/MIL composite fibers is proportional to the MIL content and decreases with temperature. Finally, cytotoxicity assays show a decrease in cell viability with increasing the MIL content.

Design of Ionic-Liquid-Based Hybrid Polymer Materials with a Magnetoactive and Electroactive Multifunctional Response.

Multifunctional materials with sensor and actuator capabilities play an increasing role in modern technology. In this scope, hybrid materials with magnetic sensing and an electromechanical actuator response based on magnetic ionic liquids (MILs) and the polymer poly(vinylidene fluoride) (PVDF) have been developed. MILs comprising different cation alkyl chain lengths [Cnmim]+ and sharing the same anion [FeCl4]- were incorporated at 20 wt % into the PVDF matrix and the morphological, physical, chemical, and functional properties of the materials were evaluated. An increasing IL alkyl chain length leads to the formation of a porous structure, together with an increase in the electroactive PVDF ß-phase content of the polymer and a decrease in the crystallinity degree and thermal stability. The magnetic susceptibility of the [Cnmim][FeCl4]/PVDF films reveals a paramagnetic behavior. The multifunctional response is characterized by a magnetoionic response that decreases with increasing IL alkyl chain length, the highest magnetoionic coefficient (1.06 ± 0.015 V cm-1 Oe-1) being observed for [C2mim][FeCl4]/PVDF. The electromechanical actuator response is characterized by a highest displacement of 1.1 mm for the [C4mim][FeCl4]/PVDF film by applying a voltage of 4 V at a frequency of 100 mHz. Further, their solution processing makes these multiresponsive materials compatible with additive manufacturing technologies.

Erratum: Development of Poly(l-Lactic Acid)-Based Bending Actuators. Polymers 2020, 12, 1187.

The authors wish to make a change to their published paper [...].

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.

Ionic-Liquid-Based Printable Materials for Thermochromic and Thermoresistive Applications.

Smart materials exhibiting thermochromic and themoresistive properties based on the electroactive polymer poly(vinylidene fluoride) (PVDF) and the ionic liquid (IL) bis(1-butyl-3-methylimidazolium) tetrachloronickelate ([Bmim]2[NiCl4]) have been developed with different contents of [Bmim]2[NiCl4] (10, 20, and 40 wt %) within the polymer matrix. The morphology of the composites is studied, and the thermochromic and thermoresistive properties are evaluated. Independently of the IL content, the PVDF/[Bmim]2[NiCl4] composites present a porous morphology and thermochromic response, revealed by the color change of the composites from transparent to dark blue, attributed to the tetrahedral complex NiCl42- formed after a dehydration process. Further, the electrical conductivity increases with increasing IL content and decreases with increasing temperature. It is also shown that the incorporation of the IL into the PVDF matrix leads to an increase in the electroactive ß phase and a decrease in the degree of crystallinity and thermal stability with increasing [Bmim]2[NiCl4] content. The printability and applicability of the developed materials as sensors are also demonstrated.