engleski

Structure of Polydispersed Colloids Characterised by Light Scattering and Electron Microscopy

The dynamics of growth and aggregation of polydispersed colloidal silver iodide particles was followed by the static light scattering method. The particles have been treated as spheres; they were stable in size in the defined time interval; this approach enables the use of the Zimm plots in order to determine the radii of gyration, and the radii of spherical particles. Stable AgI colloids, either positively or negatively charged, showed the usual Zimm diagrams, since the diagrams were untypical when the stability of the colloids decreased. The spurious Zimm diagrams showed the “curves” with envelopes, and the “curves” with minima, in the unstable domain and in the domain where the most rapid nucleation occurs, respectively. The satisfactory agreement of the particle sizes as determined by using static- and dynamic light scattering data and the values obtained from the electron microscopic images was shown. Fitting the theoretical and the experimental data P() functions showed that the particle shapes approach to the theoretical model for spheres and thin discs. The colloid stability of polydispersed aggregates was explained using also the second virial coefficients; its negative sign implies the interaction of particles in the solution; its positive value indicates the formation of new particles from the supernatant solution. In addition, the colloid stability can be characterised by mass fractal dimension. For the positive stable colloids, Dm = 2.70 ± 0.26, it can be related to the reaction controlled processes, since for the negative stable colloids, Dm = 1.97 ± 0.19, it was attributed to the diffusion controlled processes.

Electron microscopy; Light scattering; Particle size; Polydispersed colloid; Second virial coefficient; Zimm plot

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