Yield Stress Analysis With DV-III Rheometer

Abstract

The purpose of this thesis is to understand the behavior of everyday substances (toothpaste, lotions, ect.) and chemicals through the analysis of yield stress. By measuring the flow properties of these products, one can determine the stability, uses, and other properties of a substance. Yield stress is experienced everyday from squeezing a tube of toothpaste, to stirring a batch of cake batter, or canning products in a factory. Yield stress along with viscosity helps us predict the behavior of chemicals, cosmetics, and food that we handle daily. Yield stress, torque, and strain values were measured with a DV-III Rheometer and the EZ Yield software. These values were graphed using Logger Pro and Microsoft Excel to demonstrate the trends of these values and the differences of them between each sample. For example, the stress verses strain graph represents a sample’s elastic energy, plastic energy, and point at which this transition occurs. Although not measured in this paper, when metals are graphed on this curve it can provide characteristics such as the degree of brittle or ductile behavior (4). Another useful graph is showing the fluidity of a sample by using its viscosity measurements. Samples that lose flow resistance with increasing heat result in a negatively sloped linear graph on an inverse log plot. Comparing yield stress between similar polymers and different brands of mayonnaise showed an unseen difference in products of seemingly identical composition. Other comparisons can show the difference in the behavior of Newtonian, non-Newtonian, and other categories of substances