Bidirectional and Stretchable Piezoresistive Sensors Enabled by Multimaterial 3D Printing of Carbon Nanotube/Thermoplastic Polyurethane Nanocomposites

Fabricating complex sensor platforms is still a challenge because conventional sensors are discrete, directional, and often not integrated within the system at the material level. Here, we report a facile method to fabricate bidirectional strain sensors through the integration of multiwalled carbon nanotubes (MWCNT) and multimaterial additive manufacturing. Thermoplastic polyurethane (TPU)/MWCNT filaments were first made using a two-step extrusion process. TPU as the platform and TPU/MWCNT as the conducting traces were then 3D printed in tandem using multimaterial fused filament fabrication to generate uniaxial and biaxial sensors with several conductive pattern designs. The sensors were subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. It was shown that the directional sensitivity could be tailored by the type of pattern design. A wearable glove, with built-in sensors, capable of measuring finger flexure was also successfully demonstrated where the sensors are an integral part of the system. These sensors have potential applications in wearable electronics, soft robotics, and prosthetics, where complex design, multi-directionality, embedding, and customizability are demanded.

Polymer Nanocomposites via Click Chemistry Reactions

The emerging areas of polymer nanocomposites, as some are already in use in industrial applications and daily commodities, have the potential of offering new technologies with all manner of prominent capabilities. The incorporation of nanomaterials into polymeric matrix provides significant improvements, such as higher mechanical, thermal or electrical properties. In these materials, interface/interphase of components play a crucial role bringing additional features on the resulting nanocomposites. Among the various preparation strategies of such materials, an appealing strategy relies on the use of click chemistry concept as a multi-purpose toolbox for both fabrication and modulation of the material characteristics. This review aims to deliver new insights to the researchers of the field by noticing effective click chemistry-based methodologies on the preparation of polymer nanocomposites and their key applications such as optic, biomedical, coatings and sensor.

Novel Semi-IPN Nanocomposites with Functions of both Nutrient Slow-Release and Water Retention. 1. Microscopic Structure, Water Absorbency, and Degradation Performance

Few studies have been conducted on the use of general nanotechnology-based principles for providing nutrients to crops. Water and fertilizer are the most important inputs in determining crop yield and profit. In this paper, super-absorbent polymers SAP_WS (grafting wheat straw (WS) to poly(acrylic-co-acrylamide), which is WS-g-P(AA-co-AM)) and SAP_HEC (HEC (hydroxyethyl cellulose)-g-P(AA-co-AM)) and their semi-interpenetrating polymer network (semi-IPN) nanocomposites SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC (formed by chemical bonding of SAP_WS or SAP_HEC with PSRF (NPK-containing polymeric slow-release fertilizer)) were prepared. Due to the differences between activity and number of functional groups in WS and HEC, the water absorption properties and degradation performances of SAP_WS and SAP_HEC and their chemically bonded function nanocomposites SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC are different. The maximum water absorption ratios of SAP_WS, SAP_HEC, SI-PSRF/SAP_WS, and SI-PSRF/SAP_HEC can reach 200.00 g/g, 240.00 g/g, 119.91g/g, and 127.43 g/g, respectively. Effects of the structures of these four materials on their degradation performances were studied via a tomato pot experiment. The changes in microstructures of these materials during the degradation processes were characterized by TEM, SEM, FTIR, XRD, XPS, and other techniques. Results show that the degradation rate of the chemically bonded functional nanocomposites with a semi-IPN structure SI-PSRF/SAP system is higher than that of SAP+PSRF (the simple physically mixed system of PSRF and SAP). Due to the differences among the activities and quantities of functional groups in WS and HEC, the water absorption properties of SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC are different, and there are different degradation rates for these two functional nanocomposites.