<p>Pure aqueous
electrolyte solutions display a minimum in surface tension at concentrations of
~ 2 mM. This effect has been a source of
controversy since first reported by Jones and Ray in the 1930s. The Jones-Ray
effect and many other surface phenomena have frequently
been dismissed as an artifact and linked
to the presence of surface-active impurities. Herein we systematically consider
the effect of surface-active impurities by purposely adding nanomolar
concentrations of surfactants to dilute electrolyte solutions. Trace amounts of
surfactant are indeed found to decrease the surface tension and influence the
surface chemistry. However, surfactants can be removed by repeated aspiration
and stirring cycles, that eventually deplete the surfactant from solution
creating a “surface chemically pure” interface.
Upon following this cleaning procedure, a reduction in the surface tension of millimolar concentrations of salt is still observed. Consequently, we demonstrate
the Jones-Ray effect is not caused by surface
active impurities. </p>
The Jones-Ray Effect Is Not Caused by Surface Active Impurities
