Different types of impermeable fillers are usually incorporated into polymeric coating film to enhance the gas barrier properties. For instance, impermeable fillers are commonly used in barrier coating due to their larger surface, which in turn serve as barrier inclusions restricting the penetrant gas to diffuse through a longer tortuous pathway. Modeling gas transport in barrier coating can help determine the shelf-life of packaged food and reduce product development resources and time. In this paper, related tortuosity-based models corresponding to different filler geometries are outlined. This review emphasizes the emerging trends in modeling the tortuous pathway and the respective relative permeability model to predict the gas barrier performance in composite films used for barrier coating applications. We review models incorporating a range of factors, including different shapes, geometries, angular orientations, alignments, randomness in distribution, stacking, interspacing, and the polydispersity of fillers. The approaches employed to develop the tortuosity-based phenomenological models starting with simplified filler geometry and orientations to more complex morphological features of the composite films are elaborated.

The phase separation behavior of bisphenol-A-polycarbonate (PC), dissolved in N-methyl-2-pyrrolidone and dichloromethane solvents in coagulant water, was studied by the cloud point method. The respective cloud point data were determined by titration against water at room temperature and the characteristic binodal curves for the ternary systems were plotted. Further, the physical properties such as viscosity, refractive index, and density of the solution were measured. The critical polymer concentrations were determined from the viscosity measurements. PC/NMP and PC/DCM membranes were fabricated by the dry-wet phase inversion technique and characterized for their morphology, structure, and thermal stability using field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, respectively. The membranes’ performances were tested for their permeance to CO₂, CH₄, and N₂ gases at 24 ± 0.5 °C with varying feed pressures from 2 to 10 bar. The PC/DCM membranes appeared to be asymmetric dense membrane types with appreciable thermal stability, whereas the PC/NMP membranes were observed to be asymmetric with porous structures exhibiting 4.18% and 9.17% decrease in the initial and maximum degradation temperatures, respectively. The ideal CO₂/N₂ and CO₂/CH₄ selectivities of the PC/NMP membrane decreased with the increase in feed pressures, while for the PC/DCM membrane, the average ideal CO₂/N₂ and CO₂/CH₄ selectivities were found to be 25.1 ± 0.8 and 21.1 ± 0.6, respectively. Therefore, the PC/DCM membranes with dense morphologies are appropriate for gas separation applications.

The presence of the crystalline regions in poly(vinyl alcohol) coating films acts as barrier clusters forcing the gas molecules to diffuse in a longer pathway in the amorphous region of the polymer, where diffusivity and solubility are promoted in comparison. Evaluating the influence of crystalline regions on the oxygen barrier property of a semi-crystalline polymer is thus essential to prepare better coating films. Poly(vinyl alcohol) coating films with varying induced crystallinity were prepared on a polyethylene terephthalate (PET) substrate by drying at different annealing temperatures for 10 min. The coating films were first delaminated from the PET substrate and then characterized using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques to determine and confirm the induced percentage of crystallinity. The barrier performance of the coating films, i.e., the oxygen transmission rate (OTR), was measured at room temperature. Results showed a decrease in the OTR values of poly(vinyl alcohol) film with an increase in the degree of crystallinity of the polymer matrix. Tortuosity-based models, i.e., modified Nielsen models, were adopted to predict the barrier property of the semi-crystalline PVOH film with uniform or randomly distributed crystallites. A modified Nielsen model for orderly distributed crystallites with an aspect ratio of 3.4 and for randomly distributed crystallites with an aspect ratio of 10.4 resulted in a good correlation with the experimental observation. For the randomly distributed crystallites, lower absolute average relative errors of 4.66, 4.45, and 5.79% were observed as compared to orderly distributed crystallites when the degree of crystallinity was obtained using FTIR, DSC, and XRD data, respectively.

Acetone vapor sensing is important for environmental monitoring and non-invasive screening of diabetes mellitus (DM). Inhaling higher than 176 parts per million (ppm) acetone concentrations affects the respiratory system, while acetone in exhaled breath correlates with blood glucose and exhaling more than 1.8 ppm indicates the person is in danger of DM. DM is currently diagnosed invasively by measuring glucose level in blood, which is painful, and therefore inconvenient. This paper reports MEMS sensor device functionalized with blend of Chitosan/Polyethylene glycol polymers for acetone vapor sensing for possible non-invasive screening of diabetes. The sensor was experimentally tested using synthetic acetone vapor, and found to give linear response for 0.05-5 ppm acetone in air, with a sensitivity of 21 mV/ppm, good repeatability, response, and reversibility. Cross-sensitivity for 2-propanol and methanol was examined, where the responses of the sensor to 1 ppm concentration in air of these two analytes were found to be 24% and 33%, respectively, less compared to its response to the same concentration of acetone.