Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

Highly conductive and stretchy fibers are crucial components for smart fabrics and wearable electronics. However, most of the existing fiber conductors are strain sensitive with deteriorated conductance upon stretching, and thus, a compromised strategy via introducing merely geometric distortion of conductive path is often used for stable conductance. Here, we report a coaxial wet-spinning process for continuously fabricating intrinsically stretchable, highly conductive yet conductance-stable, liquid metal sheath-core microfibers. The microfiber can be stretched up to 1170%, and upon fully activating the conductive path, a very high conductivity of 4.35 × 104 S/m and resistance change of only 4% at 200% strain are realized, arising from both stretch-induced channel opening and stretching out of tortuous serpentine conductive path of the percolating liquid metal network. Moreover, the microfibers can be easily woven into an everyday glove or fabric, acting as excellent joule heaters, electrothermochromic displays, and self-powered wearable sensors to monitor human activities.

Resistive Switching and Charge Transport in Laser-Fabricated Graphene Oxide Memristors: A Time Series and Quantum Point Contact Modeling Approach

This work investigates the sources of resistive switching (RS) in recently reported laser-fabricated graphene oxide memristors by means of two numerical analysis tools linked to the Time Series Statistical Analysis and the use of the Quantum Point Contact Conduction model. The application of both numerical procedures points to the existence of a filament connecting the electrodes that may be interrupted at a precise point within the conductive path, resulting in resistive switching phenomena. These results support the existing model attributing the memristance of laser-fabricated graphene oxide memristors to the modification of a conductive path stoichiometry inside the graphene oxide.

Development of Thermally Conductive Polymer/CNF Nanocomposite Materials via PolyJet Additive Manufacturing by Improvement of Digital Material Design

PolyJet printing technology allows building polymeric materials with complex multi-material structures in the resolution of tens of microns layer thickness providing high control over the entire 3-D part. On the other hand, thermally conductive polymer/CNF nanocomposite materials offer new opportunities for replacing metals in industry and applications that require heat dissipation to avoid degradation of materials prematurely. CNFs are one of the best promising filler types to enhance thermal conductance of polymers. However, experimental thermal conductivities of polymer/CNF nanocomposites are significantly low compared to the intrinsic thermal conductivity of CNFs. Present work focused on selectively addition CNF fillers to form a thermally conductive path which helps to control dispersion and alignment. PolyJet printing forms the material and the structure simultaneously which allows the control over the material distribution and morphology on entire 3-D parts while providing possibilities to manipulate the design and create a conductive path. In the present research, improvement of thermal conductivity of Polymer/CNF nanocomposites via PolyJet printing using voxel digital printing method was investigated. Samples were designed as VeroClear material, VeroClear with CNFs, VeroCyan material, VeroCyan with CNFs. DSC and TPS were used to perform the thermal characterization of the samples.

Methodology for the additive manufacture of embedded conductive paths connecting microelectromechanical sensors using conductive and flexible filaments with extrusion devices

Purpose The purpose of this study is to explore a methodology for connecting microelectromechanical system sensors – i.e. inertial measurement unit (IMU) – to an Arduino-based microcontroller, using graphene-based conductive filament and flexible thermoplastic polyurethane (FTPU) filament and low-cost dual material extrusion technology. Design/methodology/approach A series of electrical tests were carried out to determine the maximum resistance the conductive paths may take to connect printed circuit boards (PCB). To select the most suitable printing material, three types of conductive filaments were examined. Then an experiment was carried out to find the best printing parameters in terms of printing speed, printing temperature and layer height to minimise resistivity. The size of the conductive path was also analysed. A final prototype was designed and printed according to optimised printing settings and maximum allowable resistances for each line and considering different geometries and printing strategies to reduce cross-contamination among paths. Findings For the Black Magic 3D conductive filament, the printing speed and layer height played a significant role regarding resistivity, while the printing temperature was not very important. The infill pattern of the conductive paths had to be aligned with the expected current path, while using air gaps between two adjacent paths resulted in the best approach to reducing cross-contamination. Moreover, the cross-section size of the conductive path did not affect the volume resistivity. When combined with FTPU filament constraints, the prototype yielded suitable electrical performance and printing quality when printed at a temperature of 220°C, speed of 20 mm/s and layer height of 0.2 mm. Originality/value This paper explores a systematic methodology for the additive manufacturing of commercial conductive material using low-cost extrusion technology to connect complex electronics when data transmission is a key feature.