NEUTRON REFLECTIVITY STUDIES OF AEROSOL-OT MONOLAYERS ADSORBED AT THEOIL WATER, AIR/WATER AND HYDROPHOBIC SOLID/WATER INTERFACES/

The structures of monolayers of Aerosol-OT (sodium bis(2-ethylhexyl) s ulfosuccinate) adsorbed at the oil/water, air/water and hydrophobic so lid/water interfaces have been determined using neutron specular refle ction in conjunction with isotopic substitution. The areas per molecul e were found to be 78 +/- 2 Angstrom 2 and 80 +/- 5 Angstrom(2) at the critical micelle concentration (CMC = 2.5 x 10(-3) M), increasing to 132 +/- 5 Angstrom(2) at 8.0 x 10(-6) M and 213 +/- 20 Angstrom 2 at 2 .5 x 10(-6) M at the air/water and hydrophobic solid/water interfaces respectively. The thicknesses of the AOT layer at the air/water and so lid/water interfaces were found to be 18 +/- 2 Angstrom and 15 +/- 2 A ngstrom with no significant change with concentration. At the oil/wate r interface the thickness is much larger than the fully extended molec ule and is 26 +/- 2 Angstrom at an area per molecule of 68 +/- 2 Angst rom 2. This is probably caused by roughening of the oil/water interfac e by thermal fluctuations. (C) 1998 Elsevier Science B.V.