Thermodynamics and rheology of droplet aggregation of water-in-crude oil emulsion systems

Abstract

An emulsion may be classified as a colloidal system depending on the scale analyzed. State parameters (e.g.temperature, volume fraction and osmotic pressure) determine whether the system is regarded as in a liquid-like, liquid/solid-like or solid-like phase. The transition threshold between different phases has been separately observed from thermodynamic and rheological viewpoints. For the case in which the system is under free particle motion regime (van der Waals forces, Brownian motion, depletion, etc.), we obtained a relationship between the rheological behavior and the thermodynamic state. The thermodynamic analysis is based on the McMillan-Mayer theory, and binodal curves were determined with a perturbation theory. It was that liquid-like phases behave as Newtonian, while liquid/solid-like and solid-like phases possess a non-Newtonian rheological behavior. Water-in-crude oil emulsions were used in the experiments. We studied the effect of volume fraction (φ = 20% and 30%), temperature (T = 60°C, 40°C, 25°C), and mean size diameter (dp = 6.4 μm, 5.34 μm, and 4.22 μm). The transition line from the liquid-like to the liquid-solid phase moves with volume fraction, temperature, monolayer thickness and particle diameter, consistently with the rheology results.