The suitability of carbopol 934 as a suspending agent was investigated by continuous shear and creep analysis using a concentric cylinder air turbine viscometer. Apparent vistosities determined from the apices of flow curves at a constant shear rate of 87 s−1 varied little with temperature over the range of 10–50°C. Decrease in pH from 8 to 6 caused a reduction in apparent viscosity. Non-Newtonian, pseudoplastic-like flow curves with little hysteresis were obtained for 0.1–3% w/v neutralized carbopol 934 dispersions, the magnitude of their apparent static yield value being linearly related to the polymer concentration. Analysis of creep compliance curves for carbopol dispersions showed that the material was a viscoelastic liquid at 0.5 and 1% and a viscoelastic solid at 3%.
Suspensions containing 10% w/v sulphadimidine and variable concentration of carbopol 934 gave qualitatively similar rheological results. Permanent suspensions after 6 months storage at room temperature were obtained for sulphadimidine suspensions using 0.3% or greater carbopol 934. Accelerated sedimentation tests on sulphadimidine—carbopol suspensions involving centrifugal techniques correlated well with the results of longterm sedimentation studies. Measurement of apparent static yield values and apparent viscosities at 87 s−1 of such suspensions were also found useful for predicting their longterm