Abstract:

Objective Ionic conductive elastomers have excellent stretchability and ion transport properties, which show great application prospects in flexible transparent electronic devices, medical monitoring, soft robots and other fields. However, ionic conductive elastomers suffer from the dehydration or deliquescence issues impeding their further development in extreme environment. Inspired by the “brick-and-mortar” structure derived from nacre, this research targets on the innovative design of a new type of liquid-free intrinsically ionic conductive elastomer to overcome the dehydration or deliquescence issues caused by the sensitivity of traditional ionic conductive elastomers to humidity. This breakthrough development was aimed to expand the range of materials available for applications such as wearable sensors, foldable displays, wearable optics, and more.

Method A binary polymerizable deep eutectic solvent was prepared with choline chloride and acrylic acid as raw materials in different proportions, and a ternary polymerizable deep eutectic solvent was prepared with choline chloride, acrylic acid and oxalic acid as raw materials in different proportions. The ternary polymerizable deep eutectic solvent has the fiunction of uniformly dispersing different carboxylated nanocellulose(CCNC) fibers. The three were polymerized by in situ polymerization method under 365 nm ultraviolet irradiation, obtaining D-ICE, T-ICE and T-C-ICE. The structure and properties of each material were characterized.

Results In this research, samples with different ratios of raw materials were prepared. A variety of samples with different raw material proportions were prepared, and the microstructure, electrical and mechanical properties of the related materials were measured. When the proportion of acrylic acid was too little, it was found difficult to form a stable and transparent polymerizable eutectic solvent, highlighting the necessity of introducing a new hydrogen bond donor to maintain a stable polymerizable eutectic solvent. In addition, the introduction of carboxylate nanocellulose changed the proportion of chemical bonds in the raw material. The introduction of nanocellulose also reduces the transmittance of ultraviolet light because nanocellulose itself is a solid that is opaque to light. Under these conditions, the conductivity of the material reached 5.94 mS/m. The introduction of carboxylated nanocellulose significantly improved the ionic conductivity, while the acrylic acid content decreased which has little hindrance to ionic migration after polymerization. Under these conditions, the maximum stress of the material was 0.06 MPa and the maximum strain was 130%. Carboxylated nanocellulose, with a high aspect ratio, improved the mechanical properties of the ICE. ICE became electricity conductive and a LED light was lit during the stretching process, and was recoverable to the initial state after bending and twisting, with good fatigue resistance. The results proved that the material is functional ionic conductor which is sustainable, and also indicated broad application prospects in flexible transparent electronic products and other fields.

Conclusion The flexible transparent conductive elastomers reinforced by carboxylated nanocellulose were quickly prepared by in-situ polymerization. CCNC is directly derived from natural plants, and the components of PDES are low-cost and easy to obtain, so the manufacturing process of ICE is simple, green and environmentally friendly, without harsh reaction conditions and low cost. CCNC-based ionic conductors have microscopically and macroscopically enhanced multi-stage structures, which not only provide an effective strategy for the preparation of both sustainable and functional ionic conductors, but also show broad application prospects in flexible transparent electronic products and other fields.

Key words: intrinsically ionic conductive elastomer, ternary polymerizable deep eutectic solvent, carboxylated nanocellulose, flexibility, optical transparency