Kinetics of Oil Exchange in Nanoemulsions Prepared with the Phase Inversion Concentration Method

Abstract

Nanoemulsions (NEs) are metastable emulsions with droplet sizes between 20 and 100 nm and with a wide range of applications, for example, in polymerization, in pharmaceutical and cosmetic formulations, and as drug delivery systems. Even though they are not in thermodynamic equilibrium, they can be metastable over relatively long times and have the advantage that they can be formed easily by low energy input methods. In particular, the phase inversion concentration (PIC) method allows the formation of NEs by the dilution of a suitable mixture of oil and surfactants with water. In this paper, we investigate the kinetics of the oil exchange process of NEs formed by the PIC method by looking at the exchange of different hydrophobic oils and by employing contrast variation stopped flow small-angle neutron scattering. These experiments demonstrate that this exchange becomes substantially slower by increasing the chain length of the alkane. This indicates a mechanism where monomer exchange is relevant, which would indicate also that for aging one would expect Ostwald ripening to be the determining factor. Such investigations can be carried out in a unique fashion by means of neutron scattering, and the results have important implications for the optimization of NE formulations.

Instability Mechanisms of Water-in-Oil Nanoemulsions with Phospholipids: Temporal and Morphological Structures

“…Hoffmann et al interpret small angle neutron scattering data on the exchange in nanoemulsions and conclude that only Ostwald ripening is the main mechanism for exchange. 42 They attribute the main factor for diffusion to the solubility of the dispersed alkene in water, hardly influenced by the choice of a specific surfactant. The observation of reduced Ostwald ripening with longer alkenes is in line with Kabalnov 32 and confirms theoretical expectations.…”

Philic–phobic chemical dynamics of a 1st tier dendrimer dispersed o/w nanoemulsion

“…11,12 Despite the fact that both systems have oil, water and surfactant as their constituents as well as little variations in the physicochemical attributes, the distinction prevails in terms of surfactant concentration, and thermodynamic and kinetic stabilities. [12][13][14][15][16] One of the most formidable challenges in the formation of nanoemulsions is the attainment of 1 : 1 oil-surfactant stoichiometries, where co-surfactants or additive sources can play a crucial role. Despite such immense potential to facilitate an improved structural expression of the dispersed phase, the formation of long-term stable food grade nanoemulsions has emerged as a daunting task for food chemists.…”

Nanoemulsions stabilized by non-ionic surfactants: stability and degradation mechanisms

“…17,18 In nanoemulsions stabilized by polyglycerol-4 laurate or disodium laureth sulfosuccinate, oil exchange took place via diffusion of the oil molecules through the aqueous phase, and it was concluded that coalescence played hardly any role in these systems. 19 Droplet adhesion decays with the droplet diameter, so small droplet size prevents nanoemulsions from undergoing flocculation. 20 As it is theoretically substantiated, 21 the enhanced stability of nanoemulsions towards flocculation is attributed to the high value of d/r, where d is the thickness of the adsorbed layer and r is the droplet radius.…”