Multiscale Analysis of Water-in-Oil Emulsions: A Computational Fluid Dynamics Approach

A Multiscale Approach to the Design and Manipulation of Oil-in-Water Emulsion-Based Products

Advances in computational technology and high-throughput modeling software have given rise to the tailored design of products that require accurate mathematical relationships for their assessment. Industrial emulsion-based products, ubiquitous to everyday life, are complex systems driven by interfacial phenomena that require quick property-prediction tools for their commercialization. In this work, by means of a multiscale approach, mathematical relationships to model oil-in-water emulsions and that can be applied to any commercial emulsion-based product are proposed. The energy consumption during the emulsification process ( $E_v$ , which transitions from monotonic increase to exponential growth at 80%  $w/w$ ), a parameter responsible for finished product performance, was linked to final product properties at three different levels: (i) molecular, through the dynamics of the interdroplet interactions given their distribution and structure at a microscopic level; (ii) microscopic, through average droplet size yielding an inversely proportional exponential relationship ( $D_{\left[\mathrm{4,3}\right]}\propto E_v^{-4}$ ); and (iii) macroscopic, through the plateau value of the elastic modulus and the flow behavior index leading to inversely proportional quadratic relationships ( $G^{\prime }\propto E_v^{-2}$ and $\eta \propto E_v^{-2}$ , respectively). These relationships are valid at dispersed phase concentrations beyond the 60%  $w/w$ threshold where the packing of the droplets changes the emulsion’s microscopic structure giving rise to Van der Waals forces-driven phenomena. Finding this threshold allowed expanding the concentration ranges of previously reported models. The main expectation is that these results will aid researchers and process/product designers to optimize their work in different industrial applications.

A Multi-Scale Approach to Microencapsulation by Interfacial Polymerization

This work applies a multi-scale approach to the microencapsulation by interfacial polymerization. Such microencapsulation is used to produce fertilizers, pesticides and drugs. In this study, variations at three different scales (molecular, microscopic and macroscopic) of product design (i.e., product variables, process variables and properties) are considered simultaneously. We quantify the effect of the formulation, composition and pH change on the microcapsules’ properties. Additionally, the method of measuring the strength of the microcapsules by crushing a sample of microcapsules’ suspension was tested. Results show that the xylene release rate in the microcapsules decreases when the amine functionality is greater due to a stronger crosslinking. Such degree of crosslinking increases the compression force over the microcapsules and improves their appearance. When high levels of amine concentration are used, the initial pH values in the reaction are also high which leads to agglomeration. This study provides a possible explanation to the aggregation based on the kinetic and thermodynamic controls in reactions and shows that the pH measurements account for the polyurea reaction and carbamate formation, which is a reason why this is not a suitable method to study kinetics of polymerization. Finally, the method used to measure the compressive strength of the microcapsules detected differences in formulations and composition with low sensibility.

Experimental research on the rheological properties of tailings and its effect factors

The rheological properties of tailings from gold, copper, and iron ore have been studied in this paper, using a self-developed large-scale type coaxial cylinder rheometer. The effect factors of the rheological properties of tailings, namely mineral types, particle size, plasma concentration, and the shear rate, and the influence they have on the viscosity and yield stress have also been studied. The test results showed that the viscosity of the tailings initially decreased with time and then became stable, while the yield stress initially increased with time and then tended to become stable. Three types of tailings all had a similar change trend with only small differences in value. The differences resulted from the varying mineral constituents of the tailings. The viscosity and the yield stress of the tailings increased as the concentration increased. As the shear rate decreased, the viscosity increased, but the yield stress also decreased. The change in magnitude of the yield stress increased as the concentration increased. It was also found that a larger particle size resulted in a higher viscosity and yield stress, the rise of which became more obvious at higher concentrations. The results were fitted using the exponential function of the Bingham model, and it was found that the coefficients of A₁ and A₂ changed significantly with the concentration, which indicated that A₁ and A₂ were largely influenced by other factors, and not only by the plasma concentration and particle diameter decisions. However, these functions of the Bingham model and the other coefficients of B₁ and B₂ were nearly constant. The three types of tailings also had a similar change trend for the fitted coefficients. There were some differences between the values associated with the type of tailings. For the same kind of tailings, the values of B₁ and B₂ were only slightly affected by other factors, while they were mainly influenced by the plasma concentration. The results of this research have provided the basic material for a stability study of a tailings dam and the analysis of movement law.

Mechanisms of Physical Stabilization of Concentrated Water-In-Oil Emulsions Probed by Pulse Field Gradient Nuclear Magnetic Resonance and Rheology through a Multiscale Approach

The long-term physical stability of surfactant-stabilized (Span 80 and Tween 20) concentrated water-in-mineral oil (W/O) emulsions in the presence of an electrolyte (NaCl) was studied. Pulse field gradient NMR and rheology (bulk and interfacial) were used to probe the response at the macroscopic, microscopic, and molecular levels, rendering a multiscale approach. The results show that: (1) Emulsions prepared with NaCl exhibit higher values of the elastic shear modulus ( G_with NaCl^' > G_{without NaCl}^') even after ∼20 days. (2) The stabilization effect of salt against the coarsening of droplets is not due to the differences in droplet size (and thus G') or the energy incorporated through emulsification. (3) NaCl relaxes the liquid-liquid interface via a salting-in effect, which results in a lower interfacial shear elasticity ( G_with NaCl^s' < G_{without NaCl}^s') and a higher resistance to coarsening events because of the changes in the adsorption density of the layer.