シリカミクロスフエアへのPVAの吸着とレオロジー特性に対する分子量の影響

抄録

Aqueous solutions of PVA with their average degree of polymerization(d_p)500 and 2240 were prepared, to which 0.9 μm uniform silica microspheres were dispersed. The amount of PVA adsorbed was larger on the molar basis with smaller d_p, but indifferent on the weight basis. This indicates the different molecular configuration of adsorbed PVA with different d_p. Maximum adsorption was observed at the isoelectric point of silica, i.e., around pH 3, and decreased with increasing pH. A good dispersion on the floc basis was accomplished at pH 3 with PVA concentration above 0.2wt%, irrespective of d_p. At pH 11, appreciable coagulation began above 1.0wt% for d_p 2240 and 2.0wt% for d_p 500. The PVA concentration dependence of the effective solid volume fraction, estimated from steady shear measurement is similar to that of the Bingham yield value for the suspension at pH 3. The concentration dependence was smaller at pH 11. Small but appreciable coagulation was observed at pH 11 under optical microscope with increasing PVA concentration, which is reflected on the Bingham yield value but not on the effective solid volume fraction. This, together with the value of the average occupation of PVA per unit surface are of silica, indicates that the flocculation at pH 11 is due to coacervation mechanism.