Systematic study of the flow behaviour and mechanical properties of Carbopol® Ultrez™ 10 hydroalcoholic gels

Flow behaviour and mechanical properties of 0: 100, 15:85, and 30:70 v/v gelled ethanol:water mixtures are studied as a function of pH (4.0-7.0) and Carbopol(R) Ultrez(TM) 10 concentration (0.1-0.5%). As previously reported individually for 30% v/v alcoholic Ultrez(TM) 10 gels, flow curves were adjusted to the Ostwald's model, and similar sigmoidal dose response functions were obtained to describe the pH dependence of consistency index and mechanical properties of the systems. The concentration dependence of flow indexes was also best adjusted to one-phase exponential decay functions. As a result, the influence of ethanol content on polymer network is meaningfully assessed by means of the obtained empirical parameters: bottom value of each variable (Y-max), pH value required for a 50% polymer network development (pH(50)), and asymptotic flow index value for the fully structured gels (n(min)). Also, it is assessed the influence of cosolvent on the above-mentioned empirical variables, by studying pH-dependence of gelation in methanol:water, 1-propanol: water and 1-butanol:water 15:85% v/v mixtures. As a result, the alcohol induced variations in consistency and mechanical properties of hydroalcoholic gels were well correlated to modifications in the solubility parameter (delta(T)). (C) 2002 Elsevier Science B.V. All rights reserved.