Reduced electric dipole moments and polarizabilities of rigid colloids from electric birefringence data

Abstract

Values of the electric dipole moments and polarizabilities of macromolecules and colloids vary with particle size. Determinations of “reduced” or size independent values of these parameters are often hampered owing to the finite polydispersity of practical systems. A method is proposed, whereby the electric birefringence data can be used simultaneously to yield the distribution of particle sizes (for monomodal, two parameter distributions) and reduced values of the permanent dipole moments and polarizabilities of the material. Theory is developed for rods and disks of constant thickness and ellipsoids of constant axial ratio. The theory embraces bulk and surface origins for each of the electrical parameters and for all three particle geometries. By way of an example, the theory is utilized for the interpretation of birefringence data of the rod-like clay mineral sepiolite.