Application of Thermal Lens Spectrometry to the Study of Chemical Adsorption in a Layer of a Nafion Solid Electrolyte

Thermal lens spectrometry was used to study Langmuir–Blodgett films of a weakly absorbing Nafion polyelectrolyte membrane on the surface of inert polyethylene terephthalate (PET) and glass substrates and to estimate the amount of Nafion (number of layers) using a change in the thermal characteristics of the sample. The sensitivity of thermal lens measurements at the wavelength of the exciting radiation 532.0 nm is comparable to that of solid-state spectrophotometry in the region of the maximum absorbance of Nafion (275 nm). However, the high locality of thermal lens spectrometry (the area of the signal generation zone is 100 μm²) ensures the estimation of the uniformity of the deposition of the polyelectrolyte layer. To increase the absorbance of the layer of the applied polyelectrolyte, the latter is saturated with a colored compound (ferroin). The adsorption of ferroin into the Nafion layer on the PET surface was confirmed; the absorbance of ferroin in the Nafion layer is in the range of 1 × 10–5^–5 × 10^–4 units of absorbance, which corresponds to the surface concentration of ferroin 1 × 10^–11–4 × 10^–10 mol/cm².