It is a challenge to synthesize all-in-one molecular networks that are autonomously self-healable over a wide temperature range (from subzero to high), transparent, stretchable, and conductive. Here we demonstrate the fabrication of selfhealing, transparent, conductive, and highly stretchable elastomers by a photoinitiated copolymerization of two polymerizable deep eutectic solvent (PDES) monomers, acrylic amide (AAm)/choline chloride (ChCl) and maleic acid (MA)/ChCl type PDESs. Hydrogen bonds between binary building blocks of the poly-(AAm/ChCl-co-MA/ChCl) system can readily break and reform, allowing such all organic designed elastomers to self-heal over a wide temperature ranging from −23 to 60 °C while keep a highly transparent appearance. The hypermolecular network elastomers showed a fast self-healing property (within 2 s) without any other external stimuli and excellent self-healing efficiency (up to 94%). The elastomers were highly transparent (an average transmittance of 95.1%), intrinsically conductive (an ionic conductivity of 4.0 × 10 −4 S cm −1 ), and stretchable (strains up to 450%) at room temperature. We hypothesize that this behavior will find their potential use in display and/or optically related fields of stretchable electronics in harsh environments.

Stretchable and compressible hydrogels based on natural polymers have received immense considerations for electronics. The feasibility of using pure natural polymer-based hydrogels could be improved if their mechanical behaviors satisfy the requirements of practical applications. Herein, we report highly stretchable (tensile strain ∼126%) and compressible (compression strain ∼80%) cellulose ionic hydrogels (CIHs) among pure natural polymer-based hydrogels including cellulose, chitin, and chitosan via chemical cross-linking based on free radical polymerization of allyl cellulose in NaOH/urea aqueous solution. In addition, the hydrogels have good transparency (transmittance of ∼89% at 550 nm) and ionic conductivity (∼0.16 mS cm–1) and can be worked at −20 °C without freezing and visual loss of transparency. Moreover, the CIHs can serve as reliable and stable strain sensors and have been successfully used to monitor human activities. Significantly, the various properties of hydrogel can be controlled through rationally adjusting the chemically cross-linked density. Our methodology will prove useful in developing the satisfied mechanical and transparent CIHs for a myriad of applications in flexible electronics.

3D patternable, transparent, stretchable, and conductive elastomers based on the photopolymerization of the acrylic-acid/choline-chloride deep eutectic solvent were prepared, which can serve as flexible tactile/strain sensors.

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Stretchable and antifreezing conductive hydrogels, especially prepared from natural polymers, are beneficial for important and rapidly growing stretchable electronic devices. Unfortunately, the potential value of the pure natural polymer-based hydrogel in such applications is very limited because of its poor mechanical behavior and inevitable freeze of water-based hydrogels at subzero temperatures. Herein, we report the ultrastretchable and antifreezing double-cross-linked cellulose ionic hydrogels (DCIHs) prepared by ammonium persulfate initiating free radical polymerization of allyl cellulose and by NaCl inducing physical cross-linking. The acquired hydrogels display ultrastretchability (∼236% of tensile strain) and high compressibility (∼82% of compression strain) among pure polysaccharide-based hydrogels including cellulose, chitosan, and chitin. Simultaneously the soaking strategy in saturated NaCl solution also endows the DCIHs with excellent antifreezing properties that not only have good stretchability (strain up to ∼100%) at −24 °C but also surprisingly transform into high visual transparency under a wide range of low temperature (−30 to −16 °C). In addition, the DCIH with high reliability, response speed, as well as wide range strain sensor is also demonstrated by investigating the output electrical signals, showing the potential for applications in flexible electronics under a broad range of temperature.

Macromolecular polymers with high mechanical strength usually have high crystallinity and tightly entangled segments, hindering the self-healing of fracture interfaces. In this work, we report stiff, self-healable, transparent polymer (SSHTP) materials made of hard and strong poly­(acrylamide/choline chloride) and soft and reversible poly­(acrylic acid/choline chloride) segments. SSHTPs can be easily fabricated in 1 min by photoinitiated copolymerization of two kinds of polymerizable deep eutectic solvent monomers, simultaneously obtaining high optical transmittance, superior mechanical strength, and self-healing capability. Due to the synergetic interactions of the high-density hydrogen bonds in the microphase-separated polymer matrix, damaged SSHTPs can autonomously self-heal fractures under moderate conditions, and healed SSHTPs can withstand greater than 500× their own weight without breakage. Our investigation provides a simple, feasible, and green methodology for the design of transparent healable stiff polymers which have promising applications in various industrial and technological fields.

The rational design of high-performance, flexible, transparent, electrically conducting sensor attracts considerable attention. However, these designed devices predominantly utilize glass and plastic substrates, which are expensive and not environmentally friendly. Here, novel transparent and conductive woods (TCWs) were fabricated by using renewable wood substrates and low-cost conductive polymers. Polymerizable deep eutectic solvents (PDES), acrylic-acid (AA)/choline chloride (ChCl), were used as backfilling agents and in situ photopolymerized in the delignified wood, which endowed the materials with high transparency (transmittance of 90%), good stretchability (strain up to 80%), and high electrical conductivity (0.16 S m −1 ). The retained cellulose orientation and strong interactions between the cellulose-rich template and poly(PDES) endow TCWs with excellent mechanical properties. Moreover, TCWs exhibited excellent sensing behaviors to strain/touch, even at low strain. Therefore, these materials can be used to detect weak pressure such as human being's subtle bending-release activities. This work provides a new route to fabricate functional composite materials and devices which have promising potential for electronics applications in flexible displays, tactile skin sensors, and other fields.

Ionic conductors are normally prepared from water-based materials in the solid form and feature a combination of intrinsic transparency and stretchability. The sensitivity toward humidity inevitably leads to dehydration or deliquescence issues, which will limit the long-term use of ionic conductors. Here, a novel ionic conductor based on natural bacterial cellulose (BC) and polymerizable deep eutectic solvents (PDESs) is developed for addressing the abovementioned drawbacks. The superstrong three-dimensional nanofiber network and strong interfacial interaction endow the BC−PDES ionic conductor with significantly enhanced mechanical properties (tensile strength of 8 × 10 5 Pa and compressive strength of 6.68 × 10 6 Pa). Furthermore, compared to deliquescent PDESs, BC−PDES composites showed obvious mechanical stability, which maintain good mechanical properties even when exposed to high humidity for 120 days. These materials were demonstrated to possess multiple sensitivity to external stimulus, such as strain, pressure, bend, and temperature. Thus, they can easily serve as supersensitive sensors to recognize physical activity of humans such as limb movements, throat vibrations, and handwriting. Moreover, the BC−PDES ionic conductors can be used in flexible, patterned electroluminescent devices. This work provides an efficient strategy for making cellulose-based sustainable and functional ionic conductors which have broad application in artificial flexible electronics and other products.