Color sensing of humidity using thin films of hydrophilic cationic opolymers

The possibility for color sensing of humidity at room temperature using thin films from hydrophilic cationic block copolymers of different compositions and thickness is demonstrated. Diblock copolymers of composition poly [(ethylene oxide)-b-(N, N-dimethyl acrylamide)] (PEO-b-PDMAA), the PDMAA block being modified with different amounts of quaternary ammonium groups, are synthesized via redox copolymerization in aqueous media. Silicon wafers and Bragg stacks are used as substrates for spin-coating of thin polymers films with thickness in the range 50-200 nm. The color change is quantified through calculation of CIE tristimulus color coordinates using reflectance spectra of the films measured at relative humidity (RH) of 5% and 97%. The influence offilm thickness, substrate type and chemical modification on the humidity sensitivity and color change of the films is demonstrated and discussed.