Studies in colloid optics

Summary

As a result of the study of the intensity and depolarisation of the light scattered by silicic acid solutions the following facts emerge:—

• (1) 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.

• (2) The intensity of scattering is, like viscosity, an index of the micellar growth only at the later stages of the sol-gel transformation.

• (3) 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.

• (4) 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.

• (5) In the rapid setting systems, the micelles have more of spherical asymmetry due to probably a more rapid and haphazard growth of the micelles.