Haake mars 60

The gelatinized samples described in Section 2.3 were placed between a pair of parallel plates with a diameter of 20 mm, and the gap between the plates was set at 1 mm. The evolutions of storage modulus (G′), loss modulus (G″), loss tangent (Tan δ), and dynamic viscosity (η*) in the angular frequencies between 0.63 and 66 rad/s were monitored using a rheometer (Haake Mars 60, Thermo Fisher Scientific, Waltham, MA, USA) at a strain of 1% [13 (link)].
A dynamic viscosity power function was introduced to parameterize the viscoelasticity of the sample [14 (link)], as given by Equation (1).

where η* indicates the dynamic viscosity, K* indicates the consistency coefficient, ˙ω indicates the scanning frequency, and n* indicates the flow behavior index. The K* and n* were calculated by result fitting with Equation (1).

The rheological properties of PPI with the same moisture content of 91.12% were determined using a Rheometer (HAAKE MARS 60, Thermo Fisher Scientific Inc, Yokohama, Japan) [22 (link)]. When the temperature was pushed from 10 to 90 °C at a rate of 2 °C/min, changes in rheological parameters such as elastic modulus (G’), viscous modulus (G”), and tan δ were measured.

The creams were evaluated for their appearance according to subjective organoleptic tests of colour, smell and smoothness of the cream’s application onto the skin. The pH was also determined using a digital pH meter (SevenEasyTM pH meter, Mettler Toledo, Switzerland). For this, 1 g of the cream was dissolved in 100 mL of distilled water and stored for 2 h before measuring its pH. The tests were conducted in triplicates.
Viscosity was measured using a Modular Advanced Rheometer System (HAAKE MARS 60, ThermoFisher Scientific, Bremen, Germany) at a shear rate of 0.08 s⁻¹. Dye solubility was used to identify the emulsion type, where 5 g of the prepared cream was mixed with water-soluble amaranth dye and dropped on a microscope slide. The slide was covered with a cover slip and observed under the microscope.
An accelerated stability test was performed using hot/cold cycles, where 30 g of the cream was subjected to 40 °C/75% RH for 48 h followed by 2–8 °C for 48 h. This was repeated six times. The long-term stability condition was carried out at 30 °C. 75% RH.

The systematic rheological investigation of all solutions has been performed using the rotational rheometer HAAKE MARS 60 (Thermo Fisher Scientific, Karlsruhe, Germany). Experimental data were obtained using the “cone-plate” geometry of the measuring unit with diameters of 20 and 60 mm, and the angle between conical and plate surfaces equal to 1 deg.
A protective cup was installed during the experiment to prevent moisture absorption from the air. Moreover, the sides of the measuring unit were covered with polydimethylsiloxane liquid, which prevents solvent evaporation and any contact with air humidity.
Flow curves for all solutions under study were measured at a steady-state regime of shearing in the range of shear rates from 0.1 to 1000 s⁻¹.
The frequency dependencies of the complex modulus of elasticity components storage modulus and loss modulus were measured in the frequency range of 0.628−628 rad/s in the linear domain of the viscoelastic behavior.
At least 2 of the same solutions were prepared, and 3 and more repeats were made for each concentration during experiments for the repeatability.

Rheological analyses were performed on a ThermoScientific Haake Mars 60 rheometer equipped with a 35-mm-cone-plate geometry. The analyses were performed at 20 °C with a shear rate of 10 s⁻¹.