Color sensing of humidity using thin films of hydrophilic cationic opolymers

Polymer Top-Covered Bragg Reflectors as Optical Humidity Sensors

“…This led to the alteration of T and subsequent change of the reflector's color. The implementation of the Bragg reflectors enabled the monitoring of transmittance instead of reflectance when detecting humidity, because Bragg reflectors are transparent, in contrast to the previously used silicon wafer, which is opaque [18,22]. Measuring transmittance is simple, accurate and inexpensive and therefore it is always preferable to measure reflectance.…”

“…In the first modelling step, we calculated transmittance (T1) using a particular thickness of polymer film and refractive index that equaled 1.5. Then, in the second step we increased the polymer film thickness by 30% and decreased its refractive index by 7% [22], thus simulating high humidity, and again calculated the transmittance (T2). The absolute value of the difference T1-T2, which could be regarded as a change in transmittance due to the change of humidity from 5% RH to 95% RH, is plotted in Figure 1 It is seen that ΔT increased with the thickness of the polymer film reaching steady state for thickness higher than 250 nm.…”

“…In our previous investigations [22], we have demonstrated the possibility of color sensing of humidity using a single film on an opaque (silicon) substrate. For example, the color of film with a thickness of 215 nm changes substantially from yellow to dark magenta.…”

“…To check this we calculated x, y and z CIE color coordinates using transmittance spectra measured at low and high humidity with previously developed computer code [22]. The humidityinduced changes in the CIE color coordinates x and y for a single polymer film with a thickness of 290 nm deposited on a bare glass substrate and on Bragg reflectors are shown in Figure 4b.…”

Influence of Macromolecular Architecture on the Optical and Humidity-Sensing Properties of Poly(N,N-Dimethylacrylamide)-Based Block Copolymers

“…In our previous studies, we have demonstrated the humidity-sensing ability of thin films from poly( N , N -dimethyl acrylamide)-poly(ethylene oxide) (PDMA-PEO) di- and triblock copolymers deposited by spin coating on silicon substrates [23] or on top of a Bragg stack consisting of alternating layers of SiO 2 and Nb 2 O 5 [24]. Two detection methods were explored: Measuring reflectance for single films and transmittance for the stack, and visual inspection of color in both cases [23,24]. It was shown [23,24] that the optical response to humidity of the investigated copolymer films is little influenced by copolymer composition or structure (two- or tri-component; diblock or triblock).…”