Evaluation of Nafion-Crystal Violet films for the construction of an optical relative humidity sensor

The composition of Nafion-Crystal Violet films and casting processes were s tudied in order to optimise the performance of an optical relative humidity sensor. The films were immobilised on a glass disc support, by placing a 5 .0 mu L drop of a methanolic solution of a mixture of various compositions (molar ratio) of Nafion and Crystal Violet. The homogeneity of the films, a nd also their reversibility to humidity, increased when the molar ratio of Nafion to Crystal Violet was increased. The homogeneity was even further im proved when these films were treated with a 5.0 mu L drop of methanol, lead ing to films of higher durability. The durability of films decreased with d ecrease in the film thickness. A methanol-treated, 5 mu m thickness film wi th a Nafion:Crystal Violet molar ratio of 10.1 showed a linear response ran ge from 30 to 70% relative humidity (r(2) > 0.99), with good stability and reversibility.