A stretchable, compressible and anti‐freezing ionic gel based on a natural deep eutectic solvent applied as a strain sensor

Abstract

Glycerin (Gly), a common by-product in petrochemical industry, is used as hydrogen bond donor. Green organic choline chloride (ChCl) as hydrogen bond acceptor. Natural deep eutectic solvent (NDES) can be prepared with Gly and ChCl. Subsequently, a starch/NDES ionic gel is prepared by in situ free radical polymerization of acrylamide monomer in NDES with starch as the reinforcement. The effects of amylose content in starch and starch addition amount on mechanical properties of ionic gel are analyzed. The results show that starch could be partially dissolved and dispersed in NDES. Compared with the tensile strength of pure NDES gel (about 15 kPa), the tensile strength of starch/NDES ionic gel is increased by 6 times to 90 kPa. It shows good selfrecovery performance after 20 compression cycles. Starch/NDES ionic gel has good thermal stability and frost resistance. In addition, CS4 starch/NDES ionic gel has the highest conductivity. At the same time, starch/NDES ionic gel has been successfully applied to monitor grasping motion of hand, which has the potential of strain sensor. It provides a new green method for the design of electronic products such as electronic skin.

Simultaneously Stretchable and Compressible Flexible Strain Sensors Based on Carbon Nanotube Composites for Motion Monitoring and Human–Computer Interactions

“…Strictly speaking, only a sensor that can be stretched and compressed simultaneously using the same single sample could be defined as a real stretchable and compressible sensor. However, in some of the open literature, − the sensors prepared by one material with different sizes were also called as “stretchable and compressible” sensors. For example, Hao et al fabricated cubic and film CNT/PDMS foam sensors using the same material for compression and stretch sensing, respectively, and obtained strain sensing ranges of −50 to 50%.…”

Deep eutectic solvents as an emerging green platform for the synthesis of functional materials

“…But all of the foregoing have their own flaws, so deep eutectic solvent preparation gels offers various benefits. First, because of the low toxicity and degradability of DESs, they can replace organic solvents and reduce the impact on the environment and health; second, they are renewable, so DESs can be used in combination with renewable raw materials (starch, 70 cellulose 71 ) to reduce the use of other resources; third, the use of DESs is an energy-saving low-temperature preparation method and the adjustable nature of DESs as a wider solvent system can achieve gelation at a lower temperature; fourth, DESs can be recycled and reused due to good solubility and reversibility, and through recycling, the effective use of resources can be achieved in line with the concepts of green chemistry. Most of all, there are interactions in DES gels, and the ionic conductivity is excellent, so they are also gradually becoming the material of choice for a new generation of conductive gels.…”

“…To improve this situation, it is often necessary to add other reinforcing materials, such as starch and cellulose, when adding a polymer matrix. Therefore, Yan et al 70 designed starch dispersion in NDES to form a starch/NDES mixture (Fig. 8h) and placed the hydrogel and CS4 at −26° for 24 h to observe the freeze resistance of the CS4 gel.…”