Abstract
Aqueous suspensions of polytetrafluoroethylene (PTFE) rod-like particles have been studied by electric light scattering. The investigation of the suspensions with particle concentrations 0.05, 0.1, 1 and 4 wt.% shows that for the last two concentrations the electric light scattering effect changes its sign from positive to negative when going to lower frequencies at low electric field strengths. This “anomalous” frequency behaviour is observed in semi-dilute suspensions in which the rotational volumes of the rods begin to overlap (the overlap concentration C ∗=0.52 wt.%). An increase in the ionic strength in dilute suspension (0.05% PTFE) from 5 × 10 −5 to 5 × 10 −3 M NaCl leads to a decrease in the amplitude of the effect and displacement of its relaxation frequency towards higher frequencies. These results confirm the concept that polarization of the electric double layers of the non-interacting particles is a basic cause for the kilohertz electro-optic effect.
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