Abstract
A new electrophoretic light-scattering experimental device, fully automated, compact, and very easy to use, is described. It is completely driven by a microcomputer which controls the different experiment steps, performs the data acquisition in 128, 256, or 512 points, the fast Fourier transform analysis of the photocurrent for different frequency bandwidths, 10, 20, 50, 100, 200, 500 Hz, and performs all mathematical calculations needed before displaying the results. The optical setup is a heterodyne device, using two separate beams. A focusing lens (f=30 cm) and the chosen geometry allows one to improve the signal-to-noise ratio and to work with one coherence area. A special mirror holder permits one to select scattering angles from 1° to 50°. The chamber is thermostated. Its coating (in order to minimize electro-osmosis) has an average working lifetime of 8 h. The use of this experimental device for a colloid solution of 25 mg/ℓ of TiO2 (1 μm) in 100 mg/ℓ of KCl, and 10 mg/ℓ of Na4P2O7, pH=6.8, gave an electrophoretic mobility μ=(−3.27±0.17)10−8 m2s−1 V−1 at 20 °C in good agreement with results found in the literature.
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