Forced Rayleigh scattering was used to measure the self-diffusion coefficie
nts of oil droplets dispersed in the water-continuous L-1 phase of the C12E
5/n-octane/D2O microemulsion. A single microemulsion composition of 3.7 wt
% surfactant, 4.3 wt % alkane, and 92.0 wt % water was studied at atmospher
ic pressure as a function of temperature from 17.3 to 24.5 degreesC and at
26.2 degreesC as a function of pressure from 100 to 534 bar. Droplet self-d
iffusion coefficients were found to decrease by a factor of similar to2 wit
h increasing temperature from the emulsification failure boundary to the ph
ase boundary for this L-1 phase and the lamellar phase. This decrease is at
tributed to a transition from spherical to larger nonspherical oil droplets
in water, i.e., a decrease in the spontaneous curvature of the oil/water i
nterface with increasing temperature. The effect of increasing pressure, li
ke decreasing temperature, in this region of the phase diagram is to increa
se the oil droplet self-diffusion coefficients by a factor of similar to2-3
between 220 and 540 bar. This increase is likewise attributed to a transit
ion from nonspherical to smaller spherical oil droplets in water or an incr
ease in the spontaneous curvature of the oil/water interface with increasin
g pressure. We conclude that the spontaneous curvature of the oil/water int
erface is sensitive to pressure, with increasing curvature corresponding to
increasing pressure. This conclusion is consistent with the pressure-induc
ed (2) over bar --> 3 --> 2 sequence of phase transitions observed for mixt
ures of CiEj surfactants, liquid alkanes, and water. Our results demonstrat
e the utility of forced Rayleigh scattering as a complementary experimental
technique to small:angle neutron, X-ray, and light scattering in experimen
tal studies of microemulsion microstructures at high pressures.