Carbon Nanotube Composites with Bottlebrush Elastomers for Compliant Electrodes

Abstract

Wearable electronics and biointerfacing technology require materials that are both compliant and conductive. The typical design strategy exploits polymer composites containing conductive particles, but the addition of a hard filler generally leads to a substantial increase in modulus that is not well-matched to biological tissue. Here, we report a new class of supersoft, conductive composites comprising carbon nanotubes (CNT) embedded in bottlebrush polymer networks. By virtue of the bottlebrush polymer architecture, these materials are several orders of magnitude softer than comparable composites in the literature involving linear polymer networks. For example, a CNT content of 0.25 wt % yields a shear modulus of 66 kPa while maintaining a typical conductivity for a CNT composite (ca. 10–2 S/m). An added benefit of this bottlebrush matrix chemistry is the presence of dynamic polyester bonds that facilitate thermal (re)­processing. This unique strategy of designing soft composites provides new opportunities to tailor the structure and properties of sustainable advanced materials.

Conductive and elastic bottlebrush elastomers for ultrasoft electronics

“…Thus, we selected 0.6 wt% as the highest concentration in this work. Compared to the ultralow Young’s modulus (0.63 kPa) of the pure PDMS BBE, the addition of the SWCNT fillers into the elastomer matrix increased the material’s Young’s modulus because of the reinforcement effect of the SWCNT network; however, even the highest Young’s modulus (10.65 kPa) of our SWCNT/BBE is much lower than those of conductive dry elastomers and also five times lower than that of the only previously reported conductive BBE 42 (Fig. 3d , Supplementary Fig.…”

“…1c–e ), and explore the device fabrication methods and applications based on the SWCNT/BBE. The SWCNT/BBE reveals a Young’s modulus range of 2.98–10.65 kPa and a conductivity level of 2.06–17.84 S/m, five times softer than that of the only previously reported conductive BBE 42 . To the best of our knowledge, this is also the softest conductive solvent-free elastomers ever reported.…”

“…1 ). To this end, Self et al 42 recently reported the first conductive BBE based on poly(4-methylcaprolactone) mixed with carbon nanotube (CNT) fillers, which provides a relatively low modulus of 66 kPa and an improved electrical conductivity of 0.01 S/m. The BBE preparation in this work involves a multi-step chemical synthesis of monomers and crosslinkers, which is a sophisticated process for non-experts.…”

Thermoresponsive, Recyclable, Conductive, and Healable Polymer Nanocomposites with Three Distinct Dynamic Bonds

“…Unreinforced materials were not tested because they cannot reach electrical percolation and hence do not provide measurable electrical current . Generally, since electrical percolation is less impacted by chain bridging in polymer architecture, all DPNs in this study showed electrical conductivities in the order of 10 –5 –10 –4 S/m due to only less than 1 wt % MWCNT nanoreinforcement (Figure f), suggesting that these DPNs could potentially contribute to the rapidly growing fields of flexible compliant electrodes and strain sensors …”

Conductive and Self-Healing Carbon Nanotube–Polymer Composites for Mechanically Strong Smart Materials

“…These are extremely challenging to combine into one system. Tough materials have a high mechanical modulus and strong chemical interactions, allowing for integrity against external pressure, while soft materials contain fast and exchangeable weak interactions that help the autonomous self-healing process. − Several attempts have been made to overcome this difficulty by constructing multiple cross-linking interactions. − Although these designs provide good inspiration, most materials still failed to exhibit balanced functionalities − or resulted in structures that are hard to define. , The call to develop materials with comprehensive functionalities via a simple and well-characterized synthetic route remains largely unanswered, particularly regarding conductive structures. Efforts made in the past decade to achieve these structures have primarily been the addition of transition-metal oxides or carbon materials to polymers to form composites .…”