FTIR‐ATR Study of Water Uptake and Diffusion Through Ion‐Selective Membranes Based on Plasticized Poly(vinyl chloride)

Abstract

In this paper, the water uptake and diffusion of water through ion-selective membranes based on plasticized poly(vinyl chloride) (PVC) have been studied by FTIR-ATR spectroscopy. The diffusion of water was modeled by the finite-difference method and the obtained diffusion coefficients are reported for membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) and 2-nitrophenyl octyl ether (oNPOE). The influence of various common membrane additives such as lipophilic salts and ionophores on the water uptake was also determined through representative membrane formulations (potassium tetrakis [3,5-bis(trifluoromethyl)phenyl]borate (KTFPB) and/or calcium ionophore IV (ETH 5234)). The best fits of the time dependent water concentration changes in the membrane upon water uptake were obtained with a model consisting of two diffusion coefficients describing fast (ca. 1.5 Â 10 À7 cm 2 s À1) and slow (ca. 9.5 Â 10 À9 cm 2 s À1 ) diffusion of water in the PVC membranes. In contrast to the water uptake of the membranes, the diffusion rates were found to be practically independent of the membrane composition. It is shown that KTFPB and ETH 5234 decrease the water uptake whereas it is facilitated by a higher plasticizer content of the membrane. Monomeric, dimeric, clustered and bulk water could be distinguished by deconvolution of the FTIR-ATR spectra, which is important for understanding the water uptake mechanism.

Pre-Polarized Hydrophobic Conducting Polymer Solid-Contact Ion-Selective Electrodes with Improved Potential Reproducibility

“…We found that it is better to make the potential adjustment of the SCs before 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 Water uptake of the PPy-PFOS solid contact. The water uptake of plasticized PVC-ISMs has been recently characterized by the FTIR-ATR spectroscopy 29,30,68 and the oven based coulometric Karl Fischer titration technique. 68 It was shown that water diffuses readily through the PVC-ISMs and that the water content of the membrane is influenced by the chemical composition of the electrolyte solution contacting the ISM.…”

“…[18][19][20][21] The role of the SC is to provide a stable inner phase boundary potential 20,22,23 at the substrate/SC and SC/ISM interfaces, and to prevent the aqueous layer formation at the inner interface, which coupled to diffusion of ionic species within the ISM may lead to potential instability. 24 As all ISMs exhibit water uptake [25][26][27][28][29][30][31] , the prevention of the aqueous layer formation 32,33 with ill-defined ion activity has proven to be a major challenge.…”

Characterization of Salophen Co(III) Acetate Ionophore for Nitrite Recognition

“…Among the techniques used here, ATR gives us information about the "in-situ" processes that occur in the membrane phase. In other reports, ATR-IR was primarily used for monitoring water penetration into the liquids membranes, but rarely for monitoring reaction processes within membranes [14][15][16][17][18][19]. Other techniques such UV-Vis cyclic voltammetry and potentiometry were used for validating the proper functioning of the proposed sensor.…”

Origin of the Optical Response of a Dye-doped Plasticized Poly(vinyl chloride)-based Photonic Crystal Ion Sensor

“…The transparency of plasticized PVC is altered by light scattering caused by water penetration when ions are extracted into the bulk of the PVC. 24,25 Hence, the specific peak spectra of PhC based on light diffraction and interference, strength of diffraction light was decreased. This is because, the light scattering directly reflects the decrease in diffraction intensity.…”