As a result of the study of the intensity and depolarisation of the light scattered by silicic acid solutions the following facts emerge:—
There is a continuous increase in the micellar size during the sol-gel transformation. The increase does not stop completely even after the formation of a rigid gel, though at a very small rate. Where gel-formation does not occur, the micellar growth is arrested at an intermediate stage.
The intensity of scattering is, like viscosity, an index of the micellar growth only at the later stages of the sol-gel transformation.
The micellar size in alkaline sols and gels is higher than in acid systems of the same concentration; consequently the scattering intensity is also higher.
In the slow setting systems, the micelles have almost complete spherical symmetry at a stage immediately prior to gel-formation. But it subsequently decreases due either to an orientation of the micelles in the gel or a loose chain-formation.
In the rapid setting systems, the micelles have more of spherical asymmetry due to probably a more rapid and haphazard growth of the micelles.