Near‐infrared probe for in situ characterization of nafion thin films

Abstract

SYNOPSISA near-infrared (NIR) -absorbing cyanine dye was used as a probe for in situ characterization of Nafion thin films. This NIR dye was very sensitive to changes in the hydrophobicity of the environment and proved to be very suitable for probing the Nafion coatings, which involve a two-phase structure of hydrophobic and hydrophilic zones. Sorption phenomena of water and aqueous alkali salt solutions by Nafion were investigated. For our study systems of thin-coating films prepared from 5% w t alcoholic solution of Nafion 117, the absorption spectrum was dominated by higher-order aggregates when in dry form. In pure water, the absorption maximum of the monomer dye appears at 773 nm and can be used as an indication of the swelling process of the film. The water uptake reaches saturation in only a few seconds. After the swelling process, an additional absorption band with a maximum a t 555 nm appears primarily at the expense of the NIR monomer dye absorption band. The peak transition process, which is a very slow process and is a strong function of the water content inside the matrix, can be used as an indication of the establishment of equilibrium between the two-phase structure due to the water uptake. Since the absorption maximum of the study system is around 800 nm, semiconductor lasers can be used. This technique shows high potential in other applications where polymers are used as support material, e.g., in situ thin-film thickness measurements. In the study, the feasibility of this approach was illustrated.

Metal Ion Quenching Kinetics of DTDCI in Viscous Solution and Nafion Membranes: Model System for Near Infrared Fluorescence Sensing

“…Because human skin and tissue absorption and scatter are minimized above 600 nm, fluorescence lifetime measurements with NIR sensing might be used as a convenient monitor of tissue biochemistry. [2][3][4][5] There are several key advantages in using NIR dyes in sensors such as the improvement in sensitivity resulting from low background emission from autofluorescence when using NIR excitation. Moreover, the possibility of utilizing the low cost and small size of diode lasers or light emitting diodes as the excitation source coupled to glass fibers to allow remote analysis of inaccessible regions and analytes makes NIR sensors especially attractive.…”

<title>Potential use of IR dyes for metal ion sensors</title>

“…In spite of many restrictive assumptions this model is valid in many homogeneous donor-acceptor systems8 '9, and also in some ordered media10. According to FOrster, in the absence of diffusion, the fluorescence decay function ofthe donor is I ( \L/61 I(t)=I0exp-21 (1) (2) The critical transfer distance is expressed by 6 91n(1O)K20F(i')s(i/) R0= I v (3) 128irNAn4 JO j,4…”

Near infrared studies of styrene-sodium methacrylate ionomers

“…Specific NIR studies of ionomers include the work of Ghebremeskel and coworkers, 15 which details blend interaction studies in Nylon-6/sulfonated polystyrene zinc ionomer, qualitatively examining band assignments for the specific interactions. Additionally Zen et al 16 studied Nafion in situ using NIR absorbing dyes to probe the sorption phenomena of water and alkali salt solutions. More recently, Rajagopalan et al 18 examined the NIR spectra of ethylene-co-acrylic acid and co-methacrylic acid ionomers with rare earth metals and assigned specific transitions.…”

“…Ionomer studies in the near infrared (NIR) [15][16][17][18] have not received as much attention as the midand far-infrared spectral regions. Extending from 1000 to 2500 nm, NIR is the domain of overtones and combinations involving high frequency fundamental transitions.…”