Colloids light scattering spectra

Fig. 5.8.1. Power spectrum of laser light scattered from silver chloride colloids in water. The circles are for the actual experimental data. The solid line is the sum of two Lorentzians, one centered at zero frequency, the second one at 1.97 kHz. The half-width of the first Loren-tzian is 0.35 kHz and that of the second, 0.29 kHz. The instrumental width is 50 Hz. (From Ben-Yosef et al., 1972.)...

The decrease of the aggregation of surfactant particles in the comse of reaction is confirmed by light scattering studies. A study using the turbidity spectrum showed (Fig. 2.5) that the decrease of the colloid particle concentration occms in line with the decrease of the colloid particle size. The decrease of the particle size is also confirmed by the data from viscosity-diffusion (Table 2.3). 

The application of laser Doppler velocimetry (LDV) to measure the electrophoretic mobility n of charged colloidal particles is known as laser Doppler electrophoresis (LDE). In a typical LDE experiment, an applied electric field drives the collective motion of charged colloidal particles. The particles pass through an interference pattern created by a dual-beam experimental setup (Section III.A.2). The collective electrophoretic velocity of the particles is then determined via intensity- or spectrum-based analysis of the scattered light, and the electrophoretic mobility n is calculated by dividing the velocity by the applied electric field strength. 

First, DLS measurements were conducted in the 1960s by analysing the intensity flucmations in terms of a frequency spectrum (frequency analysis— FA Cummins et al. 1964 Arrechi et al. 1967 Chu and Schones 1968 Dunning and Angus 1968). The width of the frequency spectrum is a measure of the relaxation time of the microstructural processes and can be employed for the determination of the particle diffusion coefficients (Pecora 1964). An alternative for evaluating the fluctuation of scattered light intensity is photon correlation spectroscopy (PCS), which has been used for the characterisation of colloidal suspensions since the end of the 1960s (lakeman and Pike 1969 lakeman 1970 Foord et al. 1970). PCS requires a different hardware than FA, but it can be shown that the results of both techniques are equivalent (lakeman 1970 Xu 2000, pp. 86-89). 

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