Self-Healing and Electrical Properties of Viscoelastic Polymer-Carbon Blends.

Self-healing polymer-carbon composites are seen as promising materials for future electronic devices, which must be able to restore not only their structural integrity but also electrical performance after cracking and wear. Despite multiple reports about self-healing conductive elements, there is a lack of a broad fundamental understanding of correlation between viscoelasticity of such composites, their electrical properties, and self-healing of their mechanical as well as electrical properties. Here, it is reported thorough investigation of electromechanical properties of blends of carbon black (CB) as conductive filler and viscoelastic polymers (polydimethylsiloxanes (PDMS) and polyborosiloxane (PBS)) with different relaxation times as matrices. It is shown that behavior of composites depends strongly on the viscoelastic properties of polymers. Low molecular polymer composite possesses high conductivity due to strong filler network formation, quick electrical, and mechanical properties restoration, but for this the ability is sacrificed to flow and ductility at large deformation (material is brittle). In contrary, high relaxation time polymer composite behaves elastically on small time and flows at large time scale due to weak filler network and can heal. However, the electrical properties are worse than that of carbon and viscous polymer and degrade with time.

High-Performance Liquid Metal/Polyborosiloxane Elastomer toward Thermally Conductive Applications.

With the combination of high flexibility and thermal property, thermally conductive elastomers have played an important role in daily life. However, traditional thermally conductive elastomers display limited stretchability and toughness, seriously restricting their further development in practical applications. Herein, a high-performance composite is fabricated by dispersing room-temperature liquid metal microdroplets (LM) into a polyborosiloxane elastomer (PBSE). Due to the unique solid-liquid coupling mechanism, the LM can deform with the PBSE matrix, achieving higher fracture strain (401%) and fracture toughness (2164 J/m2). Meanwhile, the existence of LM microdroplets improves the thermal conductivity of the composite. Interestingly, the LM/PBSE also exhibits remarkable anti-impact, adhesion capacities under complex loading environments. As a novel stretchable elastomer with enhanced mechanical and thermal behavior, the LM/PBSE shows good application prospects in the fields of thermal camouflages, stretchable heat-dissipation matrixes, and multifunctional shells for electronic devices.

A Highly Stretchable, Self-Healing Elastomer with Rate Sensing Capability Based on a Dynamic Dual Network.

Flexible sensing materials have attracted tremendous attention in recent years because of their potential applications in the fields of health monitoring, artificial intelligence, and so on. However, the preparation of rate sensing materials with self-healing performance is always a huge challenge. Herein, we first report the design and synthesis of a highly stretchable, recyclable, self-healing polysiloxane elastomer with rate sensing capability. The elastomer is composed of a dynamic dual network with boron/oxygen dative bonds and hydrogen bonds, which overcomes the structural instability of conventional solid-liquid materials. It exhibits certain adhesion, satisfactory mechanical robustness, and superior elongation at break (up to 1171%). After heating treatment at 80 °C for 2-4 h, the mechanical properties of damaged materials can be almost completely restored. Because of the "solid-liquid" property of the elastomer, it has irreplaceable functions which can sense different rates by resistance change after blending with multiwalled carbon nanotubes, principally in the range of 10 mm/min-150 mm/min. Especially, this rate sensing elastomer can be personalized by 3D printing at room temperature. This rate sensing strategy coupled with the introduction of dynamic dual-network structure is expected to help design advanced wearable devices for human rhythmic movement.

Synthesis of Multiwalled Carbon Nanotube-Reinforced Polyborosiloxane Nanocomposites with Mechanically Adaptive and Self-Healing Capabilities for Flexible Conductors.

Intrinsic self-healing polyborosiloxane (PBS) and its multiwalled carbon nanotube (MWCNT)-reinforced nanocomposites were synthesized from hydroxyl terminated poly(dimethylsiloxane) (PDMS) and boric acid at room temperature. The formation of Si-O-B moiety in PBS was confirmed by Fourier transform infrared spectroscopy. PBS and its MWCNT-reinforced nanocomposites were found possessing water- or methanol-activated mechanically adaptive behaviors; the compressive modulus decreased substantially when exposed to water or methanol vapor and recovered their high value after the stimulus was removed. The compressive modulus was reduced by 76%, 86%, 90%, and 83% for neat PBS and its nanocomposites containing 3.0, 6.2, and 13.3 wt % MWCNTs, respectively, in water vapor, and the modulus reduction activated by methanol vapor was greater than by water vapor. MWCNTs at higher contents acted as a continuous electrical channel in PBS offering electrical conductivity, which was up to 1.21 S/cm for the nanocomposite containing 13.3 wt % MWCNTs. The MWCNT-reinforced PBS nanocomposites also showed excellent mechanically and electrically self-healing properties, moldability, and adhesion to PDMS elastomer substrate. These properties enabled a straightforward fabrication of self-repairing MWCNT/PBS electronic circuits on PDMS elastomer substrates.