Microstructure of Ion-Selective Plasticized PVC Membranes Studied by Small-Angle Neutron Scattering

Ye, Qingshan; Borbély, and Sándor; Horvai, George

doi:10.1021/ac981416m

Cited by 32 publications

(21 citation statements)

References 27 publications

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“…This shows that during the preparation of the electrodes, the membranes de-mix, with the lower viscosity component o -NPOE preferentially entering the pores of the carbon. Indeed, separation of plasticizer and PVC in ISE sensing membranes has previously been observed at the surface of similar types of membranes 31, 32. However, in the case of the 3DOM carbon electrodes, the limited extent of demixing ensures that PVC enters the pores of the solid contact, thereby inhibiting delamination of the sensing membrane overlayer.…”

Section: Resultsmentioning

confidence: 89%

Effects of Architecture and Surface Chemistry of Three-Dimensionally Ordered Macroporous Carbon Solid Contacts on Performance of Ion-Selective Electrodes

et al. 2009

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The effects of the architecture and surface chemistry of three-dimensionally ordered macroporous (3DOM) carbon solid contacts on the properties of ion-selective electrodes (ISEs) were examined. Infiltration of the plasticized PVC membrane into the pores of the carbon created a large interfacial area between the sensing membrane and the solid contact, as shown by cryo-SEM and elemental analysis. This large interfacial area, along with the high capacitance of the 3DOM carbon solid contacts (as determined by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy) results in an excellent long-term stability of the potentiometric response, with drifts as low as 11.7 µV/h. The comparison of 3DOM carbon solid contacts with an untemplated carbon solid contact shows that the pore structure is an essential feature for the excellent electrode performance. However, the surface chemistry of the 3DOM carbon cannot be ignored. While there is no evidence for an aqueous layer forming between the sensing membrane and unoxidized 3DOM carbon, electrodes based on oxidized 3DOM carbon exhibit potentiometric responses with the typical hysteresis indicative of a water layer. A comparison of the different techniques to characterize the solid contacts confirms that constant-current charge-discharge experiments offer an intriguing approach to assess the long-term stability of solid-contact ISEs but shows that their results need to be interpreted with care.

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Section: Resultsmentioning

confidence: 89%

Effects of Architecture and Surface Chemistry of Three-Dimensionally Ordered Macroporous Carbon Solid Contacts on Performance of Ion-Selective Electrodes

et al. 2009

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“…al 32,. employing time dependent studies of polymers that were bathed in a heavy water solution for several hours.…”

Section: Methodsmentioning

confidence: 99%

Elimination of Undesirable Water Layers in Solid-Contact Polymeric Ion-Selective Electrodes

et al. 2008

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This study aims to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modern analytical chemistry (e.g., clinical chemistry using single blood droplets, modern biosensors measuring clouds of ions released from nanoparticle tagged biomolecules, lab-on-a-chip applications, etc.). This research has shown that the use of a water repellent polymethyl methacrylate/polydecyl methacrylate (PMMA/PDMA) copolymer as the ion sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid-contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ISEs. Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in-situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS) and small angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water “pooling” at the interface in areas surrounding physical imperfections in the solid-contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly twenty times longer than that for a plasticized polyvinyl chloride (PVC) ISE, and the simultaneous use of a hydrophobic POT solid-contact with a PMMA/PDMA membrane can eliminate totally this water layer problem.

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“…As a first task to elucidate the effect of the water uptake by ISMs on the analytical performance characteristics of SC-ISEs, we have studied the water uptake of highly plasticized poly(vinyl chloride) (PVC) membranes, which are the most commonly used ISMs. Only a few papers published in the 1990s by Harrison et al [24 -27], Zwickl et al [28], Ye et al [29], as well as much later by Moczar et al [30], studied the water uptake of these membranes.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2009

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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.

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Microstructure of Ion-Selective Plasticized PVC Membranes Studied by Small-Angle Neutron Scattering

Cited by 32 publications

References 27 publications

Effects of Architecture and Surface Chemistry of Three-Dimensionally Ordered Macroporous Carbon Solid Contacts on Performance of Ion-Selective Electrodes

Effects of Architecture and Surface Chemistry of Three-Dimensionally Ordered Macroporous Carbon Solid Contacts on Performance of Ion-Selective Electrodes

Elimination of Undesirable Water Layers in Solid-Contact Polymeric Ion-Selective Electrodes

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

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