On the analytical use of the Soret-enhanced thermal lens signal in aqueous solutions

The ability of micelles or polymers to affect the thermal lens response in aqueous solutions has been investigated. It is shown that the bulk thermo-optical properties of water, and consequently the pure thermal lens signal, are only slightly changed upon the addition of macromolecular species. On the contrary, the Soret effect produced by migration of micelles or polymers in the thermal gradient can significantly enhance the probe beam signal. However, the Soret contribution depends on the measurement time scale and on the relative concentrations of both the analyte and the macromolecular species. A careful analysis of the experimental data is therefore required when an analytical use of the Soret effect is considered as well as when thermo-optical parameters of such solutions are derived from the photothermal signal.