Diffusion and structure in aqueous amphiphile mixtures: Water-acetonitrile

Data are reported for the intradiffusion of water in aqueous acetonitrile solutions at 0, 10, and 25 degrees C, at pressures up to 350 MPa. At low acetonitrile concentrations, the enhancement of D-rel (=D(p)/D(0.1 MPa)) is never as high as that in pure water under the same conditions. We find no evidence for structural enhancement in this system, though this has been proposed by some past workers in interpreting certain experimental results and molecular dynamics simulations.