Highly Conductive Strong Healable Nanocomposites via Diels–Alder Reaction and Filler‐Polymer Covalent Bifunctionalization

Abstract

The covalent bonding typically provided greater mechanical strength, [12,16,[24][25][26][27][28] while weaker non-covalent bonding has been extensively investigated for healable materials. [1][2][3][4][5]18,[20][21][22][29][30][31][32][33] Different healing mechanisms were also employed together in the polymer framework, achieving high mechanical strength and efficient healing. [12] On the other hand, electrically conductive nanoparticulate fillers were physically embedded in the polymer matrix in most healable nanocomposites, without covalently bonding with the polymer matrix and actively participating in the healing process. [1][2][3][4][5]15,16,18,[30][31][32][34][35][36][37][38][39] The uniform distribution of fine nanoparticles in the polymer matrix is also challenging to achieve high σ and filler-polymer interaction. Various nanoparticles, such as silver flakes (AgFLs), [34] Ag nanowires, [16,37] Ag nanoparticles, [4,33,40] carbon nanotubes, [32,38] graphene, [35,36] and Mxene, [39] have been investigated. The conductive nanocomposites should have high electrical conductivity (σ) and mechanical strength. However, there has been a trade-off between filler-induced σ and polymer-driven mechanical strength in healable conductive nanocomposites in literature. These nanocomposites were synthesized using diverse matrix polymers such as polydimethylsiloxane, silicone rubber, polypyrrole, polyurethane, polyacrylic acid, and polyethylene glycol. [1,4,5,16,26,33] Here we report significant enhancement in both σ and mechanical strength of healable, stretchable, and conductive nanocomposites by designing covalent bonding between fillers and polymer matrix. A polystyrene-block-poly(ethyleneran-butylene)-block-polystyrene grafted with maleic anhydride (SEBSM) is designed to form reversible covalent bonding with furfuryl alcohol through the Diels-Alder (DA) reaction, resulting in an excellent healable polymer matrix (SEBSMF) with a strong mechanical strength (9.6 MPa). It is also important to uniformly disperse fine conductive nanoparticles to achieve high σ. The in-situ etching and reduction reaction of AgFLs is carried out in the SEBSMF matrix to synthesize uniformly dispersed small (7.5 nm) and medium (117 nm) silver nanosatellite (AgNS) particles with an interparticle distance of 4.3 nm. The AgNS-AgFL-SEBSMF nanocomposite has a tensile strength (14.4 MPa). It also shows a high σ (98 800 S m −1 ) Healable stretchable conductive nanocomposites have received considerable attention. However, there has been a trade-off between the filler-induced electrical conductivity (σ) and polymer-driven mechanical strength. Here significant enhancements in both σ and mechanical strength by designing reversible covalent bonding of the polymer matrix and filler-matrix covalent bifunctionalization are reported. A polystyrene-block-poly(ethylene-ranbutylene)-block-polystyrene grafted with maleic anhydride forms the strong reversible covalent bonding with furfuryl alcohol through the Diels-Alder reaction. Small (7.5 nm) and medium (117 nm) ...

In Situ Regeneration of Oxidized Copper Flakes Forming Nanosatellite Particles for Non‐Oxidized Highly Conductive Copper Nanocomposites

“…[ 26–30 ] The CuNS particles work as electrodes separated by a thin polymer (barrier width = d ) in the electrical transport through the CuNS‐SE‐CuNS arrangement (Figure 3c), similar with the recently reported electrical transport through silver nanosatellite particles embedded in polymer. [ 26–28 ] The theoretical tunneling barrier height ( λ B ) is determined by the difference between the Fermi level of CuNS particles and the electron affinity of SE (χ SE ) in case of a perfect polymer insulator with no density of states within the energy gap. [ 27,30,31 ] The work function of the regenerated non‐oxidized CuFL ( φ Cu ) is measured by Kelvin probe force microscopy (KPFM) using a gold‐coated silicon tip (Figure 3c inset).…”

“…[26][27][28][29][30] The CuNS particles work as electrodes separated by a thin polymer (barrier width = d) in the electrical transport through the CuNS-SE-CuNS arrangement (Figure 3c), similar with the recently reported electrical transport through silver nanosatellite particles embedded in polymer. [26][27][28] The theoretical tunneling barrier height (𝜆 B ) is determined by the difference between the Fermi level of CuNS particles and the electron affinity of SE (𝜒 SE ) in case of a perfect polymer insulator with no density of states within the energy gap. [27,30,31] The work function of the regenerated non-oxidized CuFL (𝜑 Cu ) is measured by Kelvin probe force microscopy (KPFM) using a gold-coated silicon tip (Figure 3c inset).…”

“…The electrical conductivity (𝜎) was measured by a laboratorybuilt four-point probe device. [26,28,45] The surface potential was measured by KPFM (Nanonavi, E-sweep) using a gold coated silicon tip. [27,28,46] The formic acid-treated CuFLs dispersed in ethanol were drop casted on a silicon wafer and dried under vacuum.…”