Cheng-Lun Hsin

Wearable strain sensors based on conductive polymer composites often cannot distinguish mechanical deformation from environmental stimuli, which limits their use in complex on-body scenarios. We address this problem through interface engineering: high-aspect-ratio ZnO nanowires (NWs), grown for 12–36 h (length 1–4 μm; diameter 100–250 nm; aspect ratio 7–28), are integrated into a poly(vinyl alcohol)/eutectic gallium–indium (PVA/EGaIn) matrix to create a nanocomposite with two coupled conduction pathways, each governed by a nanoscale interface, that respond preferentially to different stimuli. Pathway I, strain-induced coalescence of discrete EGaIn microdroplets (mean diameter 34 μm at 1500 rpm shear mixing), produces a normalized current change ΔI/I0 of 1.2 under 60% tensile strain, approximately twice the cycle-averaged response of the pristine PVA-LM control measured in parallel, while compressive loading leaves the two devices indistinguishable. Pathway II, humidity-gated ionic transport consistent with water-mediated Grotthuss proton hopping across the PVA-ZnO NW interface, yields an on/off ratio of 3.12 at 90% relative humidity (RH) and increases with NW aspect ratio at every RH tested, reflecting the larger hydroxyl-rich surface area available for interfacial water adsorption. Because the mechanical transients (seconds) are far faster than ambient humidity drift (tens of seconds to minutes), the single current output can be decomposed into a humidity-encoding baseline and a strain-encoding transient; stretch-release cycling at 45–90% RH confirms that the baseline-normalized tensile response is preserved for the 12 and 24 h devices across this range. These properties are demonstrated in a wearable human-machine interface that resolves biceps contraction against inactive-muscle baselines during exercise and converts the raw signals into quantitative workout-intensity feedback. Reversible Ga2O3 reoxidation and PVA hydrogen-bond reformation restore the insulating resting state after each stretch–release event, and alkaline treatment disassembles the composite with direct recovery of the liquid-metal phase. These results establish the nanowire aspect ratio as a practical geometric design parameter for tuning mechano-ionic transduction in end-of-life recoverable soft-matter sensors.

Thermoelectric materials offer a sustainable solution for energy harvesting. This study focuses on enhancing the thermoelectric performance of magnesium–silicide–stannide materials through the incorporation of Mn₅Si₃ nanopowders and optimization of contact metals. Results indicate that a 10 at% addition of Mn₅Si₃ to Mg_2.2(Si_0.4Sn_0.6) yields the highest ZT value of 0.25, primarily due to reduced electrical resistivity. Aluminum was identified as the optimal contact metal due to its low series resistance and high output voltage. This research demonstrates the potential of Mn₅Si₃ as a promising additive for improving the thermoelectric properties of magnesium–silicide–stannide and highlights the importance of contact metal selection in achieving optimal device performance.

In this study, intrinsic ZnO powder was sintered and intercalated with particles. The resulting powder, along with a commercial p-type product, was consolidated into bulk materials, and their thermal conductivity was measured across a temperature range of 350 K–700 K. The thermal conductivity of the commercial p-type ZnO was found to be lower than that of intrinsic ZnO, attributed to controlled doping. Notably, our demonstration illustrated that the thermal conductivity can be reduced by a factor of 5–10 in the presence of AlZn₂O₄ and ZnP₂ precipitates. This methodology presents a feasible approach for the future design of ZnO-based thermoelectric materials, particularly for thermal heat scavenging applications.

This study introduces Sn-substituted higher manganese silicides (MnSi_1.75, HMS) synthesized via an arc-melting process followed by spark plasma sintering (SPS). The influences of Sn concentrations on the thermoelectric performance of Mn(Si_1−xSn_x)_1.75 (x = 0, 0.001, 0.005, 0.01, 0.015) are systematically investigated. Our findings reveal that metallic Sn precipitates within the Mn(Si_1−xSn_x)_1.75 matrix at x ≥ 0.005, with a determined solubility limit of approximately x = 0.001. In addition, substituting Si with Sn effectively reduces the lattice thermal conductivity of HMS by introducing point defect scattering. In contrast to the undoped HMS, the lattice thermal conductivity decreases to a minimum value of 2.0 W/mK at 750 K for the Mn(Si_0.999Sn_0.001)_1.75 sample, marking a substantial 47.4% reduction. Consequently, a figure of merit (ZT) value of ~0.31 is attained at 750 K. This considerable enhancement in ZT is primarily attributed to the suppressed lattice thermal conductivity resulting from Sn substitution.