  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 a t
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 f or the crystal growth from the evolution of structure, surface
tension, and visual inspection, which can be controlled through varying the SDS
or NaCl concentrations.
