Enhanced thermal conductivity of flexible cotton fabrics coated with reactive MWCNT nanofluid for potential application in thermal conductivity coatings and fire warning

It is a challenge to fabricate a flexible and smart cotton fabric sensor with improved thermal conductivity while retaining electrical insulation. Herein, reactive multiwall carbon nanotube (MWCNT) nanofluid exhibiting soft glassy rheological behavior was successfully synthesized through simultaneous surface modification by (3-aminopropyl) triethoxysilane and dimethyloctadecyl[3-(trimethoxysilyl)propyl] ammonium chloride followed by ion-exchange reaction with nonylphenol polyoxyethylene ether sodium sulfate. Then, MWCNT nanofluid was used to coat MWCNT nanofluid/cotton fabrics by simple spraying. It was found that the addition of MWCNT nanofluid improved the thermal conductivity while preserving electrical insulation of the cotton fabric. The maximum thermal conductivity of MWCNT nanofluid/cotton fabric is 2.42 times that of cotton fabric. It was also observed that surface grafted non-conductive silane molecules and organic ion salt of MWCNT hinder the MWCNT inter-contacting with each other to form a conductive network for retaining electrical insulation. In addition, during the combustion process of cotton fabric, surface grafted organic molecules of MWCNT nanofluid began to decompose and thus promote the formation of the MWCNT conductive network, indicated by the presence of electric current. This could be valuable as a low-voltage DC power source for potential applications in fire alarm sensors.