Sol-gel approach to incorporate millimeter-long carbon nanotubes into fabrics for the development of electrical-conductive textiles

In this paper, a new and versatile approach to obtain a good dispersion in water-based paste of short (≅ 1.5 mm) and long (≅ 3.0 mm) millimeter-sized carbon nanotubes (CNT) for the fabrication of electroconductive textiles is reported. With this aim, N-[3-(triethoxysilyl)propyl]ethylenediamine (EDAES) was used in combination with a waterborne thermo-degradable surfactant to stabilize the dispersion of two different kinds of carbon nanotubes (CNT) in hydroalcoholic solutions. A polyurethane thickener was added to each CNT dispersion to obtain dense pastes that were deposited onto cotton fabrics using the knife-over-roll technique. High magnification images confirm that the nanotubes are well dispersed in both coatings, furthermore appearing homogeneously distributed on the cotton surface. The conductivity of the long CNT-coated fabrics was confirmed by the electrical resistance of 2.61 × 10⁴ Ω/sq which decreased to 9.46 × 10² Ω/sq for short CNT size. Moreover, after one washing cycle, the electrical conductivity variations of coating containing the shortest nanotubes retain over 99%, demonstrating its adhesion on the fabric. The increase of the textile stiffness was less than 20% for both treated samples compared to the reference, without affecting significantly the fabric samples comfort. The developed cotton fabrics worked well as wearable conductive materials in heart rate monitoring using photoplethysmography.