In this work, we propose a comprehensive multi-scale three-dimensional (3D) resistor network numerical model to predict the piezoresistivity behavior of a nanocomposite material composed of an insulating polymer matrix and conductive carbon nanotubes (CNTs). This material is expected to be used as highly sensitive resistance-type strain sensors due to its high piezoresistivity defined as the resistance change ratio divided by the mechanical strain. In this multi-scale 3D numerical model, three main working mechanisms, which are well known to induce the piezoresistivity of strain sensors fabricated from nanocomposites, are for the first time considered systematically. They are (a) the change of the internal conductive network formed by the CNTs, (b) the tunneling effect among neighboring CNTs, and (c) the CNTs’ piezoresistivity. Comparisons between the present numerical results and our previous experimental ones were also performed to validate the present numerical model. The influence of the CNTs’ piezoresistivity on the total piezoresistivity of nanocomposite strain sensors is explored in detail and further compared with that of the other two mechanisms. It is found that the first two working mechanisms (i.e., the change of the internal conductive network and the tunneling effect) play a major role on the piezoresistivity of the nanocomposite strain sensors, whereas the contribution from the CNTs’ piezoresistivity is quite small. The present numerical results can provide valuable information for designing highly sensitive resistance-type strain sensors made from various nanocomposites composed of an insulating polymer matrix and conductive nanofillers.

In this work, the thermal expansion properties of carbon nanotube (CNT)-reinforced nanocomposites with CNT content ranging from 1 to 15 wt% were evaluated using a multi-scale numerical approach, in which the effects of two parameters, i.e., temperature and CNT content, were investigated extensively. For all CNT contents, the obtained results clearly revealed that within a wide low-temperature range (30°C ~ 62°C), thermal contraction is observed, while thermal expansion occurs in a high-temperature range (62°C ~ 120°C). It was found that at any specified CNT content, the thermal expansion properties vary with temperature - as temperature increases, the thermal expansion rate increases linearly. However, at a specified temperature, the absolute value of the thermal expansion rate decreases nonlinearly as the CNT content increases. Moreover, the results provided by the present multi-scale numerical model were in good agreement with those obtained from the corresponding theoretical analyses and experimental measurements in this work, which indicates that this multi-scale numerical approach provides a powerful tool to evaluate the thermal expansion properties of any type of CNT/polymer nanocomposites and therefore promotes the understanding on the thermal behaviors of CNT/polymer nanocomposites for their applications in temperature sensors, nanoelectronics devices, etc.

For the development of advanced robots, there is an increasing demand to design self-adaptive envelope graspers that can take objects of unknown shapes, sizes, and softness. Inspired by the predation strategy of sea anemones, we propose a soft actuator by filling liquid into a torus. When a pulling force is applied at the interior skin of the torus, its exterior skin will roll inward and suck the target. Similar to the predation behavior of sea anemones, the inward crimping of the skin is able to grip and hold objects with different shapes, weights, and materials. By adjusting the rolling direction and length of the torus skin, the object could be engulfed, swallowed, and released. The prototype of such a gripper is fabricated, which demonstrates the versatility of application in various environments. This work provides an alternative route for designing self-adaptive graspers.

In this work, the factors affecting the nanoscratch-induced deformation of oxide glass in the completely ductile range are classified into three independent aspects, including plastic damage, densification, and chemistry-enhanced material-removal. Through comparing the deformation volume of a phosphate laser glass subject to different conditions, viz., in dry or humid air and before or after annealing, the contributions of the three factors to the total deformation were quantified and their evolution mechanisms were clarified for sustained scratching. Analyses indicate that the combined action of plastic damage and densification dominates the glass deformation in fewer-pass scratching, while plastic damage and chemistry-enhanced material-removal together determine the final deformation volume for multi-pass scratching in humid air. The results presented in this study provide further insights into the physics of glass deformation.

In this work, a fabrication process was developed to incorporate nano-SiO2 particles into poly(vinylidene fluoride) to make piezoelectric films. Experimental tests show that the piezoelectricity of the nanocomposites can be improved if the weight fraction of the additive increases within a specific range. Optical microscope images indicate that the presence of SiO2 particles can reduce the average diameter of the spherulites and increase the amount of heterogeneous nucleation sites in the PVDF matrix. In the fabrication process, stretching is used to enhance the α-β-phase transformation and orient the dipoles of the β-phase. From the experiment in which the nanocomposite films were affixed onto a vibrating beam for electricity harvesting, it was found that the output voltages of the films are dependent on not only the amplitude but also the frequency of the beam's vibration. This finding may have great potential in the field of energy harvesting using flexible piezoelectric films.