Development of an interfacial thermal lens technique: monitoring the dissolving process of amphiphilic molecules at the hexane–water interface

An interfacial thermal lens technique has been developed for monitoring amounts of molecules at a liquid–liquid interface. A thin thermal lens can be observed for amphiphilic molecules, 10-(1-pyrene)decanoic acid and 4-(1-pyrene)butanoic acid, expanded at a hexane–phosphate buffer solution interface. The thermal lens spectrophotometry offers a linear response to amounts of the expanded molecule and its minimum detectable amount is 1.0×10−10 mol corresponding about 1/100-monolayer. The signal decay depended on the pH of aqueous phase and the faster decay at lower pH was ascribed to the dissolving process of the molecules from the interface into hexane.