Effect of pressure and temperature on adiabatic compressibility of aqueoussolutions of amphiphiles with a perfluorocarbon chain

The apparent adiabatic compressibility and the apparent molar volume of sod ium perfluoroheptanoate (C6F13COONa) were obtained from the experimental da ta of ultrasound velocity and density of its aqueous solutions at the conce ntration above and below CMC (critical micelle concentration) as functions of applied pressure (0-70 MPa) and temperature (5-35 degrees C). Those were compared to the reported data for sodium decanoate (C9H19COONa) of Vikings tad et al. [J. Colloid Interface Sci. 72 (1979) 59]. It was found that the micelles of C6F13COONa were more easily compressible than C9H19COONa micell es under the condition studied. For the singly dispersed state below CMC, n egative apparent compressibility of C6F13COONa was confirmed and it approac hed to zero with the increase of pressure or temperature suggesting the dec reased electrostriction and hydrophobic hydration with pressure or temperat ure rise. (C) 2000 Elsevier Science B.V. All rights reserved.