Stretchable Conductive Polypyrrole/Polyurethane (PPy/PU) Strain Sensor with Netlike Microcracks for Human Breath Detection

Abstract

The development of wearable electronics that can monitor human physiological information demands specially structured materials with excellent stretchability and electrical conductivity. In this study, a new stretchable conductive polypyrrole/polyurethane (PPy/PU) elastomer was designed and prepared by surface diffusion and in situ polymerization of PPy inside and on porous PU substrates. The structures allowed the formation of netlike microcracks under stretching. The netlike microcrack structures make possible the reversible changes in the electrical resistance of PPy/PU elastomers under stretching and releasing cycles. The variations in morphology and chemical structures, stretchability, and conductivity as well as the sensitivity of resistance change under stretching cycles were investigated. The mechanism of reversible conductivity of the PPy/PU elastomer was proposed. This property was then used to construct a waistband-like human breath detector. The results demonstrated its potential as a strain sensor for human health care applications by showing reversible resistance changes in the repeated stretching and contracting motion when human breathes in and out.

Stretchable, Skin‐Mountable, and Wearable Strain Sensors and Their Potential Applications: A Review

“…[ 10,14,56,63,67,104,105 ] Stretching led opening and enlargement of microcracks in thin fi lms, critically limiting the electrical conduction through thin fi lms due to the separation of several microcrack edges. [ 106 ] Moreover, the electrical resistance of thin fi lms drastically increased by the applied strain. This mechanism was employed to develop highly sensitive and fl exible strain sensors.…”

“…[ 127 ] Wearable sensors gather physiological and environmental data from human body in a natural way. Measured data could be blood pressure and oxygen saturation, [ 4,128 ] breathing rate, [ 14,16,56,106 ] heartbeat, [ 5,56 ] human body temperature, [ 2,21 ] movements, [ 10,12,14 ] and beyond. Wireless or internet communications could be used to transmit the measured data from wearable sensors to a mobile phone or an access point and alter a medical center.…”

Structure and design of polymers for durable, stretchable organic electronics

“…61 These microcracks result in an increase in intrinsic device resistance and reducing the short circuit current. 62 Images of microcracks, and the effects of material stretchability can be seen in Figure 7. Interestingly, when the strain is released from a plastically deformed device, the device buckles and compresses.…”

Novel electrically conductive polyurethane/montmorillonite-polypyrrole nanocomposites

“…Among ICPs, polypyrrole (PPy) is a particularly promising material because of its high electrical conductivity, chemical and environmental stability in the oxidized state, low ionization potential, electrorheological properties, electrochromic effect and relatively easy of synthesis [1][2][3][4][5][6]. In fact, PPy can be potentially used in new advanced technology areas, including electronic and optoelectronic nanodevices [7], sensors [8][9][10][11][12][13], supercapacitors [14,15], energy storage devices [1,7,16], surface coatings for corrosion protection [17], electromagnetic shielding applications [18][19][20], smart textiles [21,22] and even in medical applications [4,[23][24][25][26]. However, the poor mechanical performances and the difficult processability (insolubility and infusibility) [2,3,19,20,27,28] have hampered the use of PPy for technological applications.…”