Development of piezoresistive PDMS/MWCNT foam nanocomposite sensor with ultrahigh flexibility and compressibility

Polymer foam nanocomposites attract great interest in many wide ranges of biomedical and healthcare monitoring applications. In this study, we investigated the effect of porosity and multi-walled carbon nanotube (MWCNT) content on the piezoresistivity, sensitivity, and mechanical properties of Polydimethylsiloxane (PDMS)/MWCNT foam nanocomposite. The foam nanocomposites were fabricated by particulate leaching method and their electrical and mechanical characteristics were investigated using the different porosity levels (60% and 70%) and different conductive nanofiller contents (0.5 wt.% and 1 wt.%). The foam nanocomposites with 0.5 wt.% MWCNT content and 60% porosity possessed higher pressure sensitivity, higher gage factor, and lower electrical hysteresis along with higher mechanical properties. Moreover, fabricated PDMS/MWCNT foam nanocomposite demonstrated high flexibility, high compressibility, and high recoverability in addition to limited mechanical hysteresis (less than 3%) with a large dynamic sensing range. Contrary to the existing foam nanocomposite samples in the literature, PDMS/MWCNT foam nanocomposites withstood higher pressure ranges (3.5–5 MPa) at limited thickness (average 2.3 mm) without experiencing noticeable macroscopic damage.

Dynamic crystallization behavior of PA-12/PP-MWCNT nanocomposites: non-isothermal kinetics approach

The effect of multi-walled carbon nanotubes (MWCNT) loading on the crystallization behavior of matrix polyamide 12 (PA-12), in PA-12/polypropylene-MWCNT (PP-MWCNT)-based nanocomposites were analyzed for their non-isothermal crystallization behavior at various cooling rates of 2.5–20 °C/min in differential scanning calorimetry (DSC). Several kinetic models such as Jeziorny (modified-Avrami), Mo and Tobin models were employed to analyze the crystallization behavioral trend with respect to time and temperature of the nanocomposites. The crystallization rate increased half-time of crystallization with MWCNT content as estimated from the Jeziorny theory. The linear agreement between Jeziorny model and experimental relative crystallinity outperforms the Tobin analysis where the coefficient of linear regression was found to be considerably trailing behind and off the satisfactory mark. The Mo model accounts for the percentage crystallinity and thereby successfully explained the crystallization behavior of PA-12 where the kinetic parameters increased with crystallinity indicating higher cooling rate for higher crystallinity. The MWCNT induced crystallization (nucleation activity) values were close to zero irrespective of MWCNT loading which reiterates the enhanced crystallization (rate) of PA-12 in the nanocomposites. Estimations based on Friedman approach showed inter-relationship between activation energy and crystallinity where the later was found to be governed by major (matrix) PA-12 phase.

Effect of Processing Temperature and the Content of Carbon Nanotubes on the Properties of Nanocomposites Based on Polyphenylene Sulfide

The study aimed to investigate the effect of processing temperature and the content of multi-wall carbon nanotubes (MWCNTs) on the rheological, thermal, and electrical properties of polyphenylene sulfide (PPS)/MWCNT nanocomposites. It was observed that the increase in MWCNT content influenced the increase of the complex viscosity, storage modulus, and loss modulus. The microscopic observations showed that with an increase in the amount of MWCNTs, the areal ratio of their agglomerates decreases. Thermogravimetric analysis showed no effect of processing temperature and MWCNT content on thermal stability; however, an increase in stability was observed as compared to neat PPS. The differential scanning calorimetry was used to assess the influence of MWCNT addition on the crystallization phenomenon of PPS. The calorimetry showed that with increasing MWCNT content, the degree of crystallinity and crystallization temperature rises. Thermal diffusivity tests proved that with an increase in the processing temperature and the content of MWCNTs, the diffusivity also increases and declines at higher testing temperatures. The resistivity measurements showed that the conductivity of the PPS/MWCNT nanocomposite increases with the increase in MWCNT content. The processing temperature did not affect resistivity.

Correlation Analysis of Heat Curing and Compressive Strength of Carbon Nanotube–Cement Mortar Composites at Sub-Zero Temperatures

Concrete curing under sub-zero temperatures causes various problems, such as initial cracking and a decrease in mechanical strength. This study investigated the effect of sub-zero ambient temperature and multi-walled carbon nanotube (MWCNT) content on the heat and strength characteristics of heat-cured MWCNT cementitious composites. The experimental parameters were the application of heat curing, MWCNT content, use of an insulation box to achieve a closed system, and ambient temperature. The results showed that the internal temperature change of the MWCNT cementitious composite increased with the ambient temperature and MWCNT content. When an insulation box was installed, the maximum temperature change of the MWCNT cementitious composite during curing increased. Furthermore, heat curing increased the compressive strength of the cementitious composite. Moreover, a microstructure analysis using field-emission scanning electron microscopy verified the formation of a MWCNT network among the cement hydrates.

Investigations on Microstructure, Mechanical, Thermal, and Tribological Behavior of Cu-MWCNT Composites Processed by Powder Metallurgy

Copper (Cu) metal matrix composite (MMC) was developed with multiwall carbon nanotubes (MWCNT) as reinforcement by using powder metallurgy (PM) technique. The composition of the composites is Cu, Cu-4 wt% MWCNT, Cu-8 wt% MWCNT, and Cu-12 wt% MWCNT. The Cu and MWCNTs were blended for 6 hours in a ball mill and compacted at a 6 ton pressure to form green compacts using a 10 ton hydraulic press. Using a tubular furnace, the heat was applied at 900°C for 1.5 hours to impart strength and integrity to the green compacts. Milled composite blends were studied to analyze its characterization through SEM and EDAX analysis. Characterization studies such as SEM and EDAX confirm the presence and even dispersion of Cu and MWCNT constituents. The relative density, hardness, and ultimate compressive strength have been studied, and a remarkable improvement in properties has been obtained by the inclusion of MWCNTs. The composites reinforced by 8 and 12 wt% MWCNT were recorded with low thermal conductivity than the Cu composite reinforced by 4 wt% MWCNT. A wear study was analyzed using Taguchi technique for determining the effect caused by the wear test parameters and MWCNT content on wear rate. The optimized parameter that contributes minimum wear rate was identified as 12 wt% MWCNT content, 10 N applied load, 2 m/s sliding velocity, and 500 m sliding distance. Based on the obtained results, it could be understood that the produced composites can be utilized for various applications like relay contact springs and switchgear, rotor bars, and bus bars.

Experimental and multiscale numerical investigations on low-velocity impact responses of syntactic foam composites reinforced with modified MWCNTs

This study focused on experimental and numerical investigations into the low-velocity impact behavior of epoxy resin matrix syntactic composites with embedded hollow glass microspheres (HGMs) and multiwalled carbon nanotubes (MWCNTs). The synergistic effects of HGMs and MWCNTs on the mechanical properties of epoxy resin composites were improved by applying amine and acid treatments to HGMs and MWCNTs, respectively. The influence of the MWCNT content and the applied impact energy on the impact responses and compression strength after the impact of these syntactic foam panel samples were discussed. The results indicated that modifying HGMs and MWCNTs contributed to improving the energy absorption and the strength retention factor (SRF) of these panels and the SRF increased with increased MWCNT content. Moreover, multiscale finite-element (FE) models were developed to simulate panel impact behavior, and modeling results were compared with experimental data. Then, the verified FE model was used to analyze the influence of CNT types (helical CNTs vs MWCNTs) and the diameter-to-thickness ratios of HGMs. This study provided a theoretical basis and design reference for a novel lightweight composite material subjected to low-velocity impact, which could be applied as a core material for sandwich structures in aerospace, marine engineering, transportation, and civil infrastructures.