2.3.4. Rheological Studies of Emulsions

Emulsions prepared according to the recipe given in point Section 2.3.4 were subjected to rheological tests. They were carried out using the RS-6000 rotational rheometer (ThermoFischer, Karlsruhe, Germany), geometry (2°, d = 35 mm)-plate, with a gap of 0.110 mm at a temperature of 20 °C. The flow curves were determined over a shear rate range between 0.1 s−1 and 500 s−1. All measurements were triplicated. In the presented work, the Cross state equation was used to describe the rheological properties:

where: η0 is the apparent viscosity at zero shear rate, Pa·s, η∞-apparent viscosity for infinite shear rate, Pa·s, γ˙-shear rate, s−1, m-flow behavior index, and K-relaxation time, s. The estimation of the parameters of rheological models containing time constants allows for determining the most probable characteristic time of the tested material. Determining the changes in the values of the constants in the Cross equations as a function of concentration allows for the formation of a view on the structure of rheological phenomena occurring during shearing. The Marquardt-Levenberg minimization procedure was used for the parameters estimation. Target function was formulated as:

where η0, η∞, K, and m were calculated. N is the number of experimental points on flow curve ηi for experimental shear rates γ˙i.