drous oxide particles in solutions of partially hydrolyzed Electric light scattering by aqueous ferric oxide suspension ( bpolyacrylamides as a continuation of our previous work on FeOOH) is investigated as a function of the concentration and the adsorption of neutral (nonhydrolyzed) polyacrylamide degree of hydrolysis of polyacrylamide (HPAM). The kilohertz on the same particles (3, 7). Supplementary measurements electro-optical effect (a s ) connected with ion polarization in the of the electrophoretic mobility of the particle/polymer comdiffuse part of electric double layers of particles decreases with plexes were carried out, indicating the isoelectric point of increasing HPAM concentration. It falls to zero near to the isoelecthe suspensions.
tric point of particles and increases again after surface recharging to a value that does not change with further polymer concentration increase. a s is shown to be independent of HPAM charge density MATERIALS AND METHODS in stabilized suspensions. In contrast, the variations of the low frequency effect (at hertz frequencies) after the isoelectric point b-FeOOH particles were obtained through acid hydroof particles correlate well with the charge of macromolecules. Similysis of 0.018 M FeCl 3 in 10 03 M HCl for three weeks at larity between the frequency behavior of the electro-optical effect room temperature ( 8 ) . The excess of Fe 3/ was removed in stabilized suspensions and the dielectric dispersion of polyelecby centrifugation. The particles obtained are ellipsoids trolyte solutions is noted. The hydrodynamic thickness of the adwith a great degree of monodispersity. The average partisorbed layer, obtained from electric light scattering, is found to be cle dimensions are obtained through electron microsindependent of the charge of macromolecules in stabilized suspencopy -long axis a ร
285 nm and short axis b ร
70 nm. sions. Its value (L r ร 10 nm) is 5-6 times smaller than the thick-The surface charge of b-FeOOH particles is due to the ness of the adsorbed uncharged polyacrylamide, indicating a flatinteraction of surface hydroxyl groups with protons. The ter conformation of the adsorbed polyelectrolyte molecules. แญง 1996 present investigation was carried out at pH ร
5.5, where Academic Press, Inc.
the particles are positively charged ( the isoelectric point is around pH ร
7 ) , and the value of the z -potential is ca. 40 mV ( 3 ) . The decrease of pH after polymer adsorption was in the range of 0.2 pH units.