Characterization of Nafion solutions and films and observation of the casting process using basic dyes as optical probes

Abstract

SYNOPSISThe absorption spectrum of methylene blue and crystal violet (CV) in ethanol-water in the presence of Nafion exhibited metachromasy, but a little or no formation of the large aggregates of the dye was observed. This indicates that the dye molecules are bound to the surface of the miceller particles of the polymer, but the ability of Nafion to induce the aggregation of the dye is weak. The absorption spectrum of malachite green (MG) and CV was measured in a cast film of Nafion at varying ambient humidity. The spectral change with humidity indicates that the decrease in the water content of the film causes the increase of H+-ion concentration in the hydrophilic cluster of Nafion and, hence, leads to the protonation of the dyes. The absorption spectrum of a Nafion solution containing MG or CV was recorded in the process of casting. The dyes changed to the protonated form right after evaporation of most solvent from the solution. This suggests that the phase inversion occurs in the casting process. 0 1995 John Wiley & Sons, Inc.

Evaluation of Nafion–Crystal Violet films for the construction of an optical relative humidity sensor

“…Electrochemical sensors employing Nafion and based on different principles of operation have been described for the determination of many different species, such as CO, 13 NO, 14 glutamate, 15 hydrazines, 16 uric acid 17 and methyl viologen. 18 Nafion has also been used as a support membrane to study the photochemical and photophysical behaviour of incorporated organic dyes and metal complexes, 12,19 and several optical sensors for metal ions, [20][21][22][23] hydrogen ion 24,25 and RH 26231 have also been developed.…”

“…When a solution of Crystal Violet and Nafion in a polar solvent is left to dry, a phase inversion occurs with the Nafion polymer and the dye remains entrapped in an ionic cluster. 19 Since the Nafion sulfonate groups are highly acidic, the Crystal Violet is in that acid environment. The acidity of the proton bound to the sulfonate group depends on the water content in the film.…”

Electrode–Electrolyte Interfacial Processes in Ionic Liquids and Sensor Applications

“…The other option is the nonaqueous electrolyte. Typically, there are three kinds of nonaqueous electrolytes: aqueous salts that could be dissolved in organic solvents (e.g., lithium perchlorate, and other perchlorate compounds, which have good solubility and ionization in particular organic solvents, such as CH 3 CN), organic compounds with charged ion center (e.g., tetra-n-butylammonium perchlorate) or polyelectrolytes (e.g., perfluorosulfonate [183,184] and Nafion ionomers [185,186]), and ILs. However, some of the aqueous electrolytes could not be dissolved in the organic solvents or cannot be ionized.…”

Uso de membranas de Nafion para a construção de sensores ópticos para medidas de pH

“…As soluções de Nafion ® /indicador foram preparadas em metanol, em diferentes razões molares, considerando que o Nafion ® possui 0,0397 mol de grupos sulfonatos por L de solução 43 . A Tabela 1 lista as soluções usadas no preparo das membranas.…”

“…Este tipo de sensor de pH pode ser empregado em sistemas específicos, como, por ex., no monitoramento contínuo de dióxido de carbono em suco gástrico 43 , com as vantagens inerentes de um sensor óptico com relação a um eletroquímico, que foram anteriormente descritas, proporcionando medidas em tempo real, que não são obtidas com o procedimento convencional de gasometria 49 . Finalmente, as determinações de pH podem ser efetuadas com base em medidas de absorbância, empregando-se um espectrofotômetro comercial.…”