Embedding Pinhole Vertical Gold Nanowire Electronic Skins for Braille Recognition

Abstract

In this context, it is crucial to improve the interfacial adhesion in order to achieve durability of current e-skin devices for real-world applications. One approach is to introduce interfacial structuring by embedding gold nanopiles into PDMS substrate, which increased its adhesive strength to 2.6 MPa due to the interlocking surface. [19] Another strategy is to introduce chemical modification in order to promote interfacial chemical bonding. A binder polymer (e.g., poly(dopamine)) has been used to promote bonding interactions between silver nanowire and PDMS, which was found to enhance durability under repeating stretching. [20] We have recently also found (3-aminopropyl) trimethoxysilane (APTMS) can efficiently promote the bonding between standing gold nanowires with Ecoflex substrates, leading to exceptionally high stretchability. [21,22] Despite of encouraging progress made so far, interfacial adhesion remains a technical challenge particularly considering the complexity of various filler materials and type of substrates.Here, we report a robust strategy to obtain e-skin patches simply by embedding vertically aligned standing gold nanowires (v-AuNWs) into PDMS. Compared to the stretchable conductor that is typically percolation networks uniformly dispersed in 3D elastomeric matrix, our v-AuNWs are vertically embedded in PDMS surface, more like 2D system yet with efficient electron transport pathways. This may in principle save material usage to achieve comparable conductivity. Unlike lying-down mode percolation network of gold nanowires reported earlier, [5,[23][24][25] our v-AuNWs were vertically grown and closely packed, with each NW connecting its neighboring NWs. A more specific comparison table between lying-down gold nanowire and our v-AuNWs in terms of strain sensitivity, stretchability, conductivity, and adhesion energy were listed in Table S1 in the Supporting Information. Besides, the v-AuNWs allow for control of surface topology by controlling seed concentration and nanowire height. With self-assembled pinhole v-AuNWs films, we could reach a high adhesion of 2.41 MPa. This enables the demonstrations of our v-AuNW-based e-skin in braille recognition. Considering the advantages of using gold in biomedical applications including high chemical inertness, biocompatibility, bandgap matching with p-type semiconductor, and wide electrochemical sensing window, [26] our pinhole v-AuNW embedding strategy may find additional applications in next-generation soft electronics.Electronic skins (e-skins) have the potential to be conformally integrated with human body to revolutionize wearable electronics for a myriad of technical applications including healthcare, soft robotics, and the internet of things, to name a few. One of the challenges preventing the current proof of concept translating to real-world applications is the device durability, in which the strong adhesion between active materials and elastomeric substrate or human skin is required. Here, a new strategy is reported to embed vertically aligned stan...

Multiscale Soft–Hard Interface Design for Flexible Hybrid Electronics

“…By manipulating the density of the nanowire, an optically transparent pinhole V-AuNW thin film could be obtained with excellent stretchability (Figure 7f). [161] Similar to the bulk nanopile gold film, the embedded V-AuNWs showed superior adhesive strength when compared to V-AuNWs directly grown on PDMS (Figure 7g).…”

“…To embed the nanowires into the elastomer, liquid PDMS was poured onto V‐AuNWs and cured to obtain a V‐AuNWs/PDMS composite (Figure e). By manipulating the density of the nanowire, an optically transparent pinhole V‐AuNW thin film could be obtained with excellent stretchability (Figure f) . Similar to the bulk nanopile gold film, the embedded V‐AuNWs showed superior adhesive strength when compared to V‐AuNWs directly grown on PDMS (Figure g).…”

“…g) Comparison of the adhesive strength of the substrate‐grown V‐AuNWs and the pinhole V‐AuNW nanopile on PDMS substrate. f,g) Reproduced with permission . Copyright 2019, Wiley‐VCH.…”

Intrinsically Stretchable Fuel Cell Based on Enokitake‐Like Standing Gold Nanowires

“…The EASA of the two kinds of electrodes are calculated to be 3.45 cm 2 for head side exposed electrode and 4.30 cm 2 for tail side exposed electrode, respectively, with the roughness factor of 6.9 and 8.6, respectively. These values are much higher than that of the bare gold electrode (a roughness factor of 1.5), and such high EASA endows them with good catalytic properties.…”

“…[32][33][34] The two as-prepared types of stretchable electrodes were first pre-treated in H 2 SO 4 solution to obtain clean surfaces for the electro-oxidation application ( Figure S1D, Supporting Information). These values are much higher than that of the bare gold electrode (a roughness factor of 1.5), [38] and such high EASA endows them with good catalytic properties. [34] The EASA of the two kinds of electrodes are calculated to be 3.45 cm 2 for head side exposed electrode and 4.30 cm 2 for tail side exposed electrode, respectively, with the roughness factor of 6.9 and 8.6, respectively.…”