ELECTRIC LIGHT-SCATTERING FROM POLYTETRAFLUOROETHYLENE SUSPENSIONS

Aqueous suspensions of polytetrafluoroethylene (PTFE) rod-like particl es have been studied by electric light scattering. The investigation o f the suspensions with particle concentrations 0.05, 0.1, 1 and 4 wt.% shows that for the last two concentrations the electric light scatter ing effect changes its sign from positive to negative when going to lo wer frequencies at low electric field strengths. This ''anomalous'' fr equency behaviour is observed in semi-dilute suspensions in which the rotational volumes of the rods begin to overlap (the overlap concentra tion C = 0.52 wt.%). An increase in the ionic strength in dilute susp ension (0.05% PTFE) from 5 x 10(-5) to 5 x 10(-3) M NaCl leads to a de crease in the amplitude of the effect and displacement of its relaxati on frequency towards higher frequencies. These results confirm 1:he co ncept that polarization of the electric double layers of the non-inter acting particles is a basic cause for the kilohertz electro-optic effe ct.