Rheological properties and microstructures of Carbopol gel network system

Abstract

Carbopol gel systems have been studied using steady, oscillatory rheology, and cryoscanning electron microscopy (cryo-SEM) analysis in order to elucidate the nature of the different microstructures of the gel in relation to polymer concentration as well as triethanolamine (TEA) content. The effect of changing the concentration of Carbopol (0.1–4 wt%) for 0, 1, and 10 wt% TEA has been investigated. Cryo-SEM revealed that honeycomb structures were observed in the gel system depending on the amount of TEA and Carbopol while the irregular fibrous three dimensional gel network systems were seen at the lower level of polymer content even in the high concentration of TEA. In addition to that, as the amount of polymer was increased, strings of fibrous network became thicker and of honeycomb-like structure. Shape of storage modulus-shear stress curve in the dynamical rheometric study was significantly changed as a result of variation in the microstructures while frequency sweep curve and yield values obtained from the model fitting in the steady rheological measurements couldn't reflect the structural difference of Carbopol gels. Two distinct relaxation phenomena were appeared with increase in polymer concentration as well as TEA concentration. Temperature dependence of the stress sweep experiment was measured and shown that the effect of temperature (1–80 °C) on the shape of the curve was the similar trend with that of TEA and polymer concentrations, although the temperature dependency on the increment was much weaker than TEA concentration.