Wearable and Stretchable Soft Electronics Based on Ultrathin Gold Nanowires

Wearable and highly flexible or stretchable electronics, including sensing devices, electrode components and energy storage devices are essential component for future human machine interfaces and bio monitoring. However, such electronics meet difficulties on current rigid and brittle wafer-based electric circuitry system. An alternative solution is to integrate the attributes of flexibility and stretchability of novel materials or novel structures to realize soft electronics. Nanotechnology offers new opportunities in designing soft electronics. <br>    Despite impressive recent advances, it remains challenging to achieve high conductivity, high stretchability and ultrathin device dimension into a single type of soft electronic device. Ultrathin gold nanowires (Au NWs) are mechanically flexible yet robust, which exhibited serpentine structure at nanoscale behaving like ‘polymer chains’ due to their ultrathin nature (2 nm in width, with an aspect ratio of >10,000). Hence, the Au NWs is intrinsically stretchable thus showing great potential in constructing novel soft electronics. <br>    To address the existing challenges, this thesis introduces a bunch of novel soft and wearable electronics based on ultrathin Au NWs. In details, we designed and fabricated highly sensitive pressure sensor, highly stretchable strain gauge sensor, flexible and transparent electrode, stretchable and transparent supercapacitor for the application of wearable biomedical monitoring, sports tracking, human machine interfacing and wearable energy supplier. In addition, ultrathin Au NWs possess several unique feature to soft electronics: 1) high sensitivity: a piezoresistive pressure sensor with sensitivity of 1.14/kPa can be achieved, which allowed real-time monitoring of human wrist pulse and tiny acoustic vibration. 2) High stretchability: a strain gauge sensor based on Au NWs thin film with thickness of only 1.64 μm could be working at strains exceeding 350%, >100 times larger than its metal counterparts. 3) High transparency and conductivity: we explored a simple yet efficient solution-based bottom-up strategy to fabricate Au NWs mesh film which could achieve both high transparency (>92%) and conductivity. 4) Ultrathin device dimensions: due to soft and serpentine-like geometry of ultrathin Au NWs, well-aligned Au NWs thin film (8 nm in thickness) could achieve high transparency (>90% at 550 nm) and excellent stretchability (>50%) simultaneously. <br>    Thus, the aim of this project is to develop a general and inexpensive strategy to construct wearable electronic devices based on ultrathin gold nanowires. We believed our strategies opened a new route to future wearable electronics. <br> <br

Manufacturable Conducting Rubber Ambers and Stretchable Conductors from Copper Nanowire Aerogel Monoliths

We report on a low-cost, simple yet efficient strategy to fabricate ultralightweight aerogel monoliths and conducting rubber ambers from copper nanowires (CuNWs). A trace amount of poly(vinyl alcohol) (PVA) substantially improved the mechanical robustness and elasticity of the CuNW aerogel while maintaining a high electrical conductivity. The resistivity was highly responsive to strains manifesting two distinct domains, and both followed a power law function consistent with pressure-controlled percolation theory. However, the values of the exponents were much less than the predicted value for 3D systems, which may be due to highly porous structures. Remarkably, the CuNW-PVA aerogels could be further embedded into PDMS resin, forming conducting rubber ambers. The ambers could be further manufactured simply by cutting into any arbitrary 1D, 2D, and 3D shapes, which were all intrinsically conductive without the need of external prewiring, a condition required in the previous aerogel-based conductors. The outstanding electrical conductivity in conjunction with high mechanical compliance enabled prototypes of the elastic piezoresistivity switches and stretchable conductors

Unconventional Janus Properties of Enokitake-like Gold Nanowire Films

We report on unconventional Janus material properties of vertically aligned gold nanowire films that conduct electricity and interact with light and water in drastically different ways on its two opposing sides. These Janus-like properties originate from enokitake-like nanowire structures, causing the nanoparticle side (“head”) to behave like bulk gold, yet the opposing nanowire side (“tail”) behaves as discontinuous nanophases. Due to this Janus film structure, its head side is hydrophilic but its tail side is hydrophobic; its head side reflects light like bulk gold, yet its tail side is a broadband superabsorber; its tail side is less conductive but with tunable resistance. More importantly, the elastomer-bonded Janus film exhibits unusual mechatronic properties when being stretched, bent, and pressed. The tail-bonded elastomeric sheet can be stretched up to ∼800% strain while remaining conductive, which is about 10-fold that of head-bonded film. In addition, it is also more sensitive to bending forces and point loads than the corresponding tail-bonded film. We further demonstrate the versatility of nanowire-based Janus films for pressure sensors using bilayer structures in three different assembly layouts

Unconventional Janus Properties of Enokitake-like Gold Nanowire Films

We report on unconventional Janus material properties of vertically aligned gold nanowire films that conduct electricity and interact with light and water in drastically different ways on its two opposing sides. These Janus-like properties originate from enokitake-like nanowire structures, causing the nanoparticle side (“head”) to behave like bulk gold, yet the opposing nanowire side (“tail”) behaves as discontinuous nanophases. Due to this Janus film structure, its head side is hydrophilic but its tail side is hydrophobic; its head side reflects light like bulk gold, yet its tail side is a broadband superabsorber; its tail side is less conductive but with tunable resistance. More importantly, the elastomer-bonded Janus film exhibits unusual mechatronic properties when being stretched, bent, and pressed. The tail-bonded elastomeric sheet can be stretched up to ∼800% strain while remaining conductive, which is about 10-fold that of head-bonded film. In addition, it is also more sensitive to bending forces and point loads than the corresponding tail-bonded film. We further demonstrate the versatility of nanowire-based Janus films for pressure sensors using bilayer structures in three different assembly layouts