ABSTRACT
Rheology studies the flow and deformation of materials. Thus, the knowledge of the rheological and mechanical properties is important for product design, production, quality control, and for predicting shelf storage stability. Rheology studies can assist scientists in formulating optimal products (1). Conventionally, a single-point viscosity tests are widely used, but they not adequate in characterizing the full rheological profile of these materials, and thus, it is better to generate the full viscosity curves to capture a wide range of material responses (2). There are several tests conducted to characterize a material. The first one implies plotting viscosity as a function of a stress ramp at constant temperature and within a specific time interval. Usually, at low stresses viscosity might remain constant, and then a critical stress point is reached were viscosity decreases abruptly. The magnitude of the resulting slope confirms the shear sensitivity of the material (3). Another highly used plot involves the viscosity versus shear rate. Usually, at low shear rates viscosity remains constant and then it decreases steadily. Further, from the stress ramp test the minimum shear stress required to initiate flow (Yield stress) is determined. The higher the yield value, the more readily a dispersion will maintain particles in suspension with minimal sedimentation. However, a low yield stress might be useful for a product to improve the sensorial properties such as the ease of spreading onto a surface forming a short-term thin layer (4).