Interface-templated crystal growth in sodium dodecyl sulfate solutions with NaCl


Many ionic surfactants, such as sodium dodecyl sulphate (SDS) crystallize out of solution if the temperature falls below the crystallization boundary. The crystallization temperature is impacted by solution properties, and can be decreased with the addition of salt. We have studied SDS crystallization at the liquid/vapor interfaces from solutions at high ionic strength (sodium chloride). We show that the surfactant crystals at the surface grow from adsorbed SDS molecules, as evidenced by the preferential orientation of the crystals identified using grazing incidence X-ray diffraction. We find a unique timescale for the crystal growth from the evolution of structure, surface tension, and visual inspection, which can be controlled through varying the SDS or NaCl concentrations.