Structure of micelles and micro-emulsions probed through the molecular reorientation of water

We study the structural properties of dodecyltrimethylammonium bromide (DTAB) micelles and micro-emulsions by probing the molecular reorientation of water with polarization-resolved infrared pump-probe spectroscopy. For all systems studied, we observe that a fraction of water reorients on a much slower timescale than bulk water. This slow water fraction increases sublinear with increasing DTAB concentration, indicating an increase of the micelle size and enhanced micelle aggregation with concentration. We observe that the addition of oil to the micelle solutions, leading to the formation of a micro-emulsion, does not lead to a significant change of the fraction of slow water, showing that the added oil molecules are well solvated within the core of the micelles, and thus completely shielded from water.