Rheological characterization of hydroalcoholic gels--15% ethanol--of Carbopol Ultrez 10

The rheological behaviour of Carbopol Ultrez 10 ethanolic (15%) gels was studied as a function of two main variables: pH (4.0-7.0) and the polymer concentration (0.1-0.5%). Flow curves of all hydroalcoholic gels were adjusted to the Ostwald model. Sigmoidal dose response functions were obtained to describe the pH dependence of consistency index of the systems. The concentration dependence of flow indexes was best adjusted to one-phase exponential decay functions. Finally, by substituting in the power law expression, an empirical model is given to estimate viscosities of gels for any value of pH and polymer concentration in the ranges evaluated. As a result, the influence of the variables on polymer network is meaningfully assessed by means of the obtained empirical parameters: bottom value (Ymax), pH value required for a 50% polymer network development (pH50), and asymptotic flow index value for the fully structured gels (n(min)).