Novel cellulose and polyamide halochromic textile sensors based on the encapsulation of Methyl Red into a sol–gel matrix

pH-sensitive chromic textiles are promising materials that can be used as flexible sensor systems providing an easily visible signal. However to date, mainly conventional dyeing techniques have been applied for obtaining these textile sensors, which limits the possibilities in terms of pH-sensitive dyes and textile types. Therefore, the more versatile sol–gel technique was studied in this paper as an alternative dye loading method. The pH-indicator Methyl Red was applied on cellulosic and synthetic textile fabrics using both a conventional dyeing and a sol–gel technique. Textile fabrics treated with sol–gel were found to show a fast and clearly visible colour change with a pH-variation. In addition, the hydrophilicity of the polymeric material affected the distribution of the dye molecules inside the fibre and as a consequence the response of the resulting sensor. Moreover, due to interactions of Methyl Red with the sol–gel matrix the halochromic behaviour of the dye changed with respect to the dye in solution. In conclusion, sol–gel showed to be a highly effective technique for the development of flexible sensors which allow for monitoring pH-variations through a colour change.