A spectrometer for the detection of laser light scattered by thermally excited capillary waves at fluid interfaces is described. Its optical system makes possible precise observations at capillaly mode wave numbers high enough to avoid significant effects of instrumental resolution and permits the beam to be incident upon the fluid interface through either of the two adjacent fluid phases. Its performance was tested on the following three model systems at 20.C: the free surfaces of water and 2-butano1, representing the oscillatory and critically damped capillary wave regimes respectively, and the interface between mutually saturated phases of these two liquids, representing the non-oscillatory regime. Accessible wave numbers for which effects of instrumental resolution were insignificant ranged between approximately 1 x lo5 and 5 x lo5 m-'. Values obtained for surface and interfacial tensions and viscosity agreed well with those obtained using a high-accuracy Wilhelmy plate tensiometer and a capillary viscometer.
We have performed scattered light intensity autocorrelation measurements on a Winsor type microemulsion system composed of brine, cyclohexane, SDS and a mixture of 1-butanol and 1-pentanol. At high cosurfactant concentration, where the microemulsion phase was considered to consist of individual, spherical water-in-oil droplets of relatively low droplet volume fraction, the autocorrelation functions were observed to be essentially single exponential, as expected. Above a certain droplet volume fraction, however, additional decay modes were observed to enter the correlation data. These modes were interpreted to be due to rotation and/or internal motion of droplet aggregates.
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