Laser-induced liquid-to-droplet extraction of chlorophenol: photothermal phase separation of aqueous triethylamine solutions.

Thermal phase separation of aqueous triethylamine (TEA) solutions (TEA wt % = 6.5-6.7 in H2O) was induced by irradiating a focused 1064-nm laser beam (spot size approximately 1 mum) under an optical microscope, and this produced a single micrometer-sized TEA droplet as demonstrated by in situ Raman microspectroscopy. Since H2O absorbs 1064-nm light, heat is generated at the focal spot of the incident laser beam, giving rise to photothermal phase separation of the aqueous TEA solution. The TEA droplet produced by phase separation was trapped simultaneously by the incident laser beam. In the presence of p-chlorophenol (CP) in an aqueous TEA solution, laser-induced photothermal phase separation and simultaneous TEA droplet formation brought about extraction/concentration of CP from the surrounding solution phase to the TEA droplet (approximately 15-mum diameter and 1.7-pL volume). Raman microspectroscopy demonstrated that the distribution coefficient of CP (KD) between the solution phase and the single TEA droplet was KD(drop) = approximately 21, while that in a bulk TEA/H2O system was KD(bulk) = 4.7. The larger KD(drop) value as compared to KD(bulk) was discussed in terms of radiation pressure exerted on CP in the TEA droplet.