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Abstract:A new optical pH sensor based on polysulfone (PSU) and polyaniline (PANI) was developed. A transparent and flexible PSU membrane was employed as a support. The electrically conductive and pH-responsive PANI was deposited onto the membrane surface by in situ chemical oxidative polymerization (COP). The absorption spectra of the PANI-coated PSU membranes exhibited sensitivity to pH changes in the range of 4-12, which allowed for designing a dual wavelength pH optical sensor. The performance of the membranes was assessed by measuring their response starting from high pH and going down to low pH, and vice versa. It was found that it is necessary to precondition the sensor layers before each measurement due to the slight hysteresis observed during forward and backward pH titrations. PSU membranes with polyaniline coating thicknesses in the range of «100-200 nm exhibited fast response times of <4 s, which are attributed to the porous, rough and nanofibrillar morphology of the polyaniline coating. The fabricated pH sensor was characterized by a sigmoidal response (R 2 = 0.997) which allows for pH determination over a wide dynamic range. All membranes were stable for a period of more than six months when stored in 1 M HCl solution. The reproducibility of the fabricated optical pH sensors was found to be <0.02 absorption units after one month storage in 1 M HCl solution. The performance of the optical pH sensor was tested and the obtained pH values were compared with the results obtained using a pH meter device.

The chelation behavior of the phenolic-formaldehyde polymers, poly(2,4dihydroxybenzoic acid-3,5-diylmethylene) polymer I, poly(2-hydroxybenzoic acid-3,5-diylmethylene) polymer II, and poly(3-hydroxybenzoic acid-4,6-diylmethylene) polymer III toward the trivalent lanthanide metal-ions, La 3þ , Nd 3þ , Sm 3þ , Gd 3þ , and Tb 3þ was studied by a static batch equilibration technique at 258C as a function of contact time, pH, and counter ion. The highest metal-ion uptake of these polymers was achieved at pH 7.0 and by using perchlorate as the counter ion. Results of the study revealed that polymer I has the highest metal-ion 721 uptake capacity, and that the metal-ion uptake falls in the order: Tb 3þ . Gd 3þ . Sm 3þ . Nd 3þ . La 3þ .

There is an increasing demand for sustainable and safe packaging technologies to improve consumer satisfaction, reduce food loss during storage and transportation, and track the quality status of food throughout its distribution. This study reports the fabrication of colorimetric pH-indicative and flame-retardant nanocomposite films (NCFs) based on polyvinyl alcohol (PVA) and nanoclays for smart and safe food packaging applications. Tough, flexible, and transparent NCFs were obtained using 15% nanoclay loading (PVA-15) with superior properties, including low solubility/swelling in water and high thermal stability with flame-retardant behavior. The NCFs showed average mechanical properties that are comparable to commercial films for packaging applications. The color parameters were recorded at different pH values and the prepared NCFs showed distinctive colorimetric pH-responsive behavior during the transition from acidic to alkaline medium with high values for the calculated color difference (∆E ≈ 50). The prepared NCFs provided an effective way to detect the spoilage of the shrimp samples via monitoring the color change of the NCFs during the storage period. The current study proposes the prepared NCFs as renewable candidates for smart food packaging featuring colorimetric pH-sensing for monitoring food freshness as well as a safer alternative choice for applications that demand films with fire-retardant properties.

A new optical pH sensor based on Polysulfone (PSU) and Polyaniline (PANI) was developed. The transparent and flexible PSU membrane was employed as a support. The electrically conductive and pH-responsive PANI was deposited onto the membrane surface by in situ chemical oxidative polymerization (COP). The absorption spectra of the PANI-coated PSU membranes exhibited sensitivity to pH changes in the range of 4-12, which allowed for designing dual wavelength pH optical sensor. The performance and durability of the membranes were assessed by measuring their response starting from high pH and going down to low pH, and vice versa. The effect of synthesis conditions and film thickness were investigated. The effect of the membrane's storage conditions on the reproducibility of the results was also investigated.