Role of the Secondary Minimum on the Flocculation Rate of Nondeformable Droplets

Abstract

The kinetic stability of suspensions is usually associated with a decrease in the flux of flocculating particles due to the action of a repulsive potential. However, previous calculations on bitumen drops suggest the possible occurrence of relatively fast aggregation rates in systems with large electrostatic barriers for primary minimum flocculation. This indicates a strong effect of the secondary minimum in the process of aggregation. Here, emulsion stability simulations (ESS) are used to study the aggregation behavior of 11 systems showing different depths of the secondary minimum and three particle sizes. Micron size drops (as those of Bitumen emulsions) usually exhibit deep secondary minima, which rarely occur between nanometer size particles. At high surfactant concentrations, these drops do not coalesce but can still show fast aggregation rates caused by irreversible secondary-minimum flocculation. On the other hand, the extent of coalescence in nanometer-size systems markedly depends on the height of the repulsive barrier. Furthermore, the secondary minimum of these smaller particles is usually shallow, causing reversible aggregation or no aggregation at all. In this article, the consequences of the referred behaviors on the magnitude of the stability ratio are discussed.

Theoretical estimation of stability ratios for hexadecane-in-water (H/W) emulsions stabilized with nonylphenol ethoxylated surfactants

“…We studied this problem previously (see Refs. [27,85]) concluding that if coalescence is regarded as an instantaneous process that occurs as the surfaces of the particles touch, Eq. (4) applies.…”

“…The details of this procedure can be found in Refs. [27,85]. In summary, a distance d f , slightly larger than the position of the secondary minimum of each potential is introduced as input in an additional code.…”

Turbiscan Lab® Expert analysis of the stability of ethosomes® and ultradeformable liposomes containing a bilayer fluidizing agent

“…Various components of vesicle formulations are able to modify the fluidity of lipid bilayers [1,2], beside influencing colloidal stability. In fact, a reversible sedimentation of vesicles can occur when different pharmaceutical components are present in concentrated colloidal suspensions [3]. This effect is increased if a vesicular bilayer fluidizing agent (i.e.…”

Influence of Drop Deformability on the Stability of Decane‐in‐Water Emulsions

“…34 and 35, the values of the surface charge density (r T ) corresponding to the experimental measurements were found. Although the values of r T also allowed the estimation of the effective surfactant charge (z s ), the experimental surface charge was used in all simulations [22,57]. These data are reported in Tables 1 and 2 for DOSS and NaOl emulsions, respectively.…”