Rapid Microwave Polymerization of Porous Nanocomposites with Piezoresistive Sensing Function

Abstract

In this paper, polydimethylsiloxane (PDMS) and multi-walled carbon nanotube (MWCNT) nanocomposites with piezoresistive sensing function were fabricated using microwave irradiation. The effects of precuring time on the mechanical and electrical properties of nanocomposites were investigated. The increased viscosity and possible nanofiller re-agglomeration during the precuring process caused decreased microwave absorption, resulting in extended curing times, and decreased porosity and electrical conductivity in the cured nanocomposites. The porosity generated during the microwave-curing process was investigated with a scanning electron microscope (SEM) and density measurements. Increased loadings of MWCNTs resulted in shortened curing times and an increased number of small well-dispersed closed-cell pores. The mechanical properties of the synthesized nanocomposites including stress–strain behaviors and Young’s Modulus were examined. Experimental results demonstrated that the synthesized nanocomposites with 2.5 wt. % MWCNTs achieved the highest piezoresistive sensitivity with an average gauge factor of 7.9 at 10% applied strain. The piezoresistive responses of these nanocomposites were characterized under compressive loads at various maximum strains, loading rates, and under viscoelastic stress relaxation conditions. The 2.5 wt. % nanocomposite was successfully used in an application as a skin-attachable compression sensor for human motion detection including squeezing a golf ball.

PDMS Sponges with Embedded Carbon Nanotubes as Piezoresistive Sensors for Human Motion Detection

“…The mechanical properties were not significantly affected by the varied loading of CNTs with a relatively consistent compressive modulus of 160 ± 29 kPa between all the sensors. No significant trend was found for the compressive modulus or porosity of each sensor, likely due to significant variations in viscosity between the nanocomposite resins [ 17 ], variations in sugar particle sizes, and potential inhomogeneity during the mixing, resulting in spatial porosity variations in the samples ( Figure S1 ). Representative stress–strain curves for the sponges with varied CNT loadings and consistent sugar porogen loading of 70 wt% are shown in Figure 6 c. The electrical properties were significantly impacted by the nanofiller loading as the measured resistance was an order of magnitude different between CNT loadings of 1.5 wt% and 3 wt%.…”

“…Highly flexible piezoresistive pressure sensors typically decrease their electrical resistance under compressive strain mainly due to movement of conductive nanoparticles forming new conductive networks. Additional mechanisms have been developed and employed to improve the sensitivity of flexible piezoresistive sensors by implementing SiO 2 microparticles to break apart conductive networks [ 15 ], microcracks on a highly conductive surface [ 16 ], and porosity [ 17 ]. Particularly, introducing porosity in flexible sensors has received considerable attention due to facile fabrication methods, enhanced compressibility and sensitivity, and increased commercial applications [ 18 ].…”

“…To solve these problems, one potential solution is to implement microwave processing techniques during nanocomposite fabrication. In our previous studies, microwave irradiation was utilized to rapidly cure PDMS/CNT nanocomposites in 25 s or less due to the strong microwave absorption of CNTs [ 17 ]. The major findings from these microwave-curing studies included significantly enhanced electrical conductivity [ 31 ], decreased compressive modulus, and unaffected piezoresistive sensitivity of the nanocomposite sensors [ 32 ].…”

Radio frequency heating and material processing using carbon susceptors

“…3 These include Joule or resistive heating, [4][5][6][7] induction heating, 8 vibrational heating, 9 ultrasonic heating and welding, 10 infrared heating, 11 and electromagnetic heating. 12,13 Specically, electromagnetic heating is a rapidly emerging eld that has several advantages including rapid, non-contact, non-invasive, and material-selective volumetric heating.…”

Toward Enhanced Humidity Stability of Triboelectric Mechanical Sensors via Atomic Layer Deposition

“…To satisfy societal demands, various sensors based on the piezoresistive effect [ 1 , 2 , 3 ], capacitive sensing [ 4 , 5 , 6 ], and piezoelectric behavior [ 7 , 8 , 9 ] have been investigated. Triboelectric effect-based sensors have been investigated to develop reliable mechanical and chemical sensors.…”