Magnetic birefringence as a tool for determining adsorbed polymer layer thicknesses

Abstract

Suspensions of small elongated magnetic particles show birefringence when subjected to a magnetic field. The decay of the birefringence upon removal of the field is used to obtain the rotational diffusion coefficient of the particles, which in turn reveals the hydrodynamic thickness of an adsorbed polymer layer. Results are given for gelatin in water and for cellulose nitrate and a few other polymers in organic solvents. With a.c. magnetic fields, polymer layer thicknesses can be observed continuously.