Rheological Characterization of Gels

Forty-eight hours after preparation of the gels, rheological measurements were determined in triplicate with a rotational rheometer (Haake Rheostress 1, Thermo Fischer Scientific, Karlsruhe, Germany) provided with a cone–plate setup (the gap between cone and plate was 0.106 mm), with a plate and a movable higher cone Haake C60/2° Ti (60 mm diameter, 2° angle). The rheometer was equipped with a Thermo Haake Phoenix II + Haake C25P temperature controller device (Thermo Fischer Scientific, Waltham, MA, USA) and operated by a HaakeRheowin^® Job Manager v. 4.0 (Thermo Fischer Scientific, Waltham, MA, USA) for testing and HaakeRheowin^® Data Manager v.4.0 (Thermo Fischer Scientific, Waltham, MA, USA) for analysis of the acquired data. Viscosity and flow curves were measured at 25 °C. The conditions of the shear rate ramp program adjusted a 3 min ramp-up period from 0 to 50 s⁻¹, a 1 min uniform-shear-rate period from 50 s⁻¹, and a ramp down from 50 to 0 s⁻¹ for 3 min. The rotational flow curve values were fitted to various mathematical model equations: Newton, Ostwald-de-Waele, Bingham, Casson, Cross, and Herschel–Bulkley [20 (link)]. The best fit of mathematical models was based on the correlation coefficient value (r). The mean viscosity value (Pa·s) was evaluated from the uniform share section at 50 s⁻¹ for each formulation.