Amphiphilic Poly(vinyl Alcohol) Copolymers Designed for Optical Sensor Applications—Synthesis and Properties

Abstract

A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance using hydrophobically modified PVA copolymers is studied. Series of poly(vinylalcohol-co-vinylacetal)s (PVA–Ac) of acetal content in the range 18%–28% are synthesized by partial acetalization of hydroxyl groups of PVA with acetaldehyde and thin films are deposited by spin-coating using silicon substrates and glass substrates covered with Au–Pd thin film with thickness of 30 nm. Sensing properties are probed through reflectance measurements at relative humidity (RH) in the range 5%–95% RH. The influence of film thickness, post-deposition annealing temperature, and substrate type/configuration on hysteresis, sensitivity, and accuracy/resolution of humidity sensing is studied for partially acetalized PVA copolymer films, and comparison with neat PVA is made. Enhancement of sensing behavior through preparation of polymer–silica hybrids is demonstrated. The possibility of color sensing is discussed.

Flexible and Transparent Polymer-Based Optical Humidity Sensor

“…Amphiphilic PVA-Ac copolymer with 24% acetal content was synthesized by hydrophobic modification of PVA (Fluka; 98% hydrolyzed; average polymerization degree 1600) with acetaldehyde (Fluka; ≥99%) as already described in [44,45]. Briefly, acetalization was carried out in aqueous solution of PVA of concentration 25 g•L −1 .…”

“…The content of acetal groups was estimated to be 24% from the 1 H NMR spectrum of the copolymer (Figure S1) by comparing the integrated peak areas of the methine protons of PVA (peak 2 and 4) to the methine protons of acetal rings (peak 5). The LCST behavior of the copolymer is known to be dependent on the extent of acetalization [45] and was evaluated by means of UV-Vis spectroscopy using a DU 800 Beckman Coulter (Brea, CA, USA) spectrophotometer. Transmittance at a wavelength of 500 nm of copolymer aqueous solution was studied as a function of temperature and the characteristic cloud point temperature of 30 • C was confirmed from the clouding curve (Figure S2).…”

Magnetron Sputtering Thin Films as Tool to Detect Triclosan in Infant Formula Powder: Electronic Tongue Approach

“…The concentration response of the e-tongue is indicated by this negative value (−1.9) of sensitivity [42], demonstrating, from Figure 5a, that the sensitivity decreases with the increase of the concentration. The sensor resolution [43], corresponding to the lowest concentration that can be detected (the limit of detection) and may be found near the lowest used concentration (C s ). The C s value was 10 −15 M, while the minimum value that could be measured was 0.23.…”

Moisture-Responsive Polymer Films on Flexible Substrates for Optical Sensing of Humidity

“…The next step was the deposition of the Au:Pd/PVA-Ac24 films on the flexible substrates and glass, after which the transmission spectra were measured. Refractive index n and extinction coefficient k values of thin films of PVA-Ac24 with a thickness about 80 nm were previously calculated [18] and taken at wavelength of 600 nm −1.45 and 0.017, respectively, from measured reflectance spectra of the polymer deposited on silicon wafer. The spectra of PET covered with Au:Pd/PVA-Ac24 is very close to the spectra of the same structure deposited on glass, as seen in Figure 1b.…”