A near-field optical method for probing liquid–liquid interfaces

A high resolution method to study the interface between two immiscible liquids is presented. The technique is based on the combination of a near-field optical probe and Raman spectroscopy. This combination brings together high local resolution in tip direction and the capability for molecular analysis at the interface. First trans-phase boundary Raman profiles on the p-xylene/ethylene glycol system measured with a spatial resolution of 1 μm are presented. Changes in the Raman bands due to the influence of the phase boundary extend as far as 10 μm from the phase boundary itself. Studies with coated and uncoated near-field probes demonstrate the important role of the optical near field in the experiments.