Highly Concentrated Emulsions: Role of Droplet Size

Abstract

The problem of droplet size dependence on rheological properties of highly concentrated emulsions was studied. Changes in droplet size distribution were achieved by multi-pass flow through a small orifice set as the outlet of a piston-chamber pumping instrument, and extended elongation of droplets combined with the transienttransition flow regime (laminar=turbulent) at the outlet of the orifice provided the shift of the droplet sizes to the smaller-size side of the distribution. Their distributions were wider and of the logarithmic-normal distribution type. Two models were proposed and used to fit the refinement evolution and the width of distributions respectively. The droplet size versus number of pumping cycles was expressed by the fitting parameters, h D , h x , D crit. , x crit. , and C, which, in turn, gave a clear estimation of factors that influence refinement during pumping. These factors involved surfactant type and surfactant concentration, where higher surfactant concentration induced higher efficiency with regard to droplet disruption. The most important part of the result of the investigation is, however, the experimental proof that the shear modulus versus droplet size is not necessarily expressed by a linear reciprocal dependence, but by an exponent equal to 2. It was shown that the stability of highly concentrated emulsions in shearing is determined by some critical value of deformation with reference to the yielding conditions. This value on average equalled 0.07 for all samples under investigation.

Biomass Lignin Stabilized Anti-UV High Internal Phase Emulsions: Preparation, Rheology, and Application As Carrier Materials

“…The viscosity of the HIPEs increased significantly when the dosage of SDS was increased from 0.8 to 1.0 wt %. This finding is in agreement with the reported results that the reduction in droplet average diameter would significantly improve the properties of the emulsions, such as the viscosity, yield stress, and storage modulus, which is caused by the thinner intervening liquid layers between the droplets result in tighter packing of droplets and higher effective viscosity. − When the dosage of SDS used was above 1.0 wt %, the viscosity of the HIPEs decreased, even though the droplet size decreased. The possible reason for this observation is that SDS contributed more on stabilizing the emulsions at high SDS dosage, a part of EHL was liberated and played the role of dispersant, which results in lower viscosity.…”

“…The 5.0 wt % EHL and 1.0 wt % SDS costabilized HIPEs have the largest yield stress when the oil content is 80 vol %. This further demonstrates that smaller droplet size and tighter overall droplet packing resulted in a thicker emulsion, which is more resistant to the deformation and also beneficial for the stability of HIPEs. − Both |η*| and tan δ are important parameters for the storage stability of dispersions. Larger |η*| values and lower tan δ values present better stability and elastic behavior for emulsions in the linear viscoelastic region .…”

Effect of Incorporation of Multiwalled Carbon Nanotubes on the Microstructure and Flow Behavior of Highly Concentrated Emulsions

“…HCEs are characterized as viscoplastic liquids with complex flow behavior. A number of studies were reported on the influence of various governing factors on the rheological characteristics of HCEs, and emulsion explosives in particular. − …”

Roles of NaCl in Enhancing the Stability of Water-in-Oil High Internal Phase Emulsions

“…For HIPEs with a defined composition and internal/external phase volume fraction, the decrease in MDD greatly altered the rheological properties of the emulsion. 56 This was evidenced by the dramatic increase in the viscosity, σ c , and G′ values. At higher PGPR concentrations, the droplets showed smaller MDD, which improved the shear resistance of the emulsions.…”