Colloidal behavior of nanoemulsions: Interactions, structure, and rheology

Abstract

Nanoemulsions exhibit unique behavior due to their nanoscopic dimensions, including remarkable droplet stability, interactions and rheology. These properties are significantly enhanced by nanoscopic droplet size, as well as selection of surfactant and other molecular species in solution. Electrostatic and polymer-induced interdroplet interactions are particularly powerful tools for fine-tuning the interdroplet interactions, and have led to stimuli-responsive nanoemulsion systems that provide deep insight into their unique properties. As such, nanoemulsions have emerged as powerful model systems for studying a number of colloidal phenomena including suspension rheology, repulsive and attractive colloidal glasses, aggregation processes, colloidal gelation and phase instability, and associative network formation in polymer-colloid mixtures. This review summarizes recent advances in understanding the colloidal behavior of nanoemulsions, and provides a unifying framework for understanding the various complex states that emerge, as well as perspective on emerging challenges and opportunities that will advance the use of nanoemulsions in both fundamental colloid science and technological applications. Highlights We review efforts to understand & control colloidal behavior of nanoemulsions.  Electrostatic and polymer-induced interdroplet interactions are discussed.  Repulsive interactions lead to jammed and compressed states at low volume fraction.  Attractive interactions lead to clustering, gelation and colloidal phase separation.  Nanoemulsions are model fluids to study arrested states in colloidal dispersions.

Synthesis of Oil-Laden Poly(ethylene glycol) Diacrylate Hydrogel Nanocapsules from Double Nanoemulsions

“…The average droplet size decreases as more mechanical energy is added to the system until a size plateau is reached, whereby the deformations applied to the fluid are no longer sufficient to break up the droplets. 47 These droplet sizes are corroborated by cryo-TEM ( Figure 1a). The stability of the nanoemulsions was determined by measuring the droplet size over time ( Figure 1c).…”

“…The stability of the nanoemulsions was determined by measuring the droplet size over time ( Figure 1c). As expected for nanoemulsions of such a small size, 47,49 these droplets are extremely stable, with no appreciable change in diameter over multiple months ( Figure 1c). Single W/O2 nanoemulsions were formed by ultrasonication of a coarse emulsion of hydrogel precursor solution in cyclohexane with Span80 and Tween80 as co-surfactants, similar to a system used in previous work to generate uniform nanogel particles.…”

“…When keeping the composition constant, the final size of the nanoemulsion can be controlled by adjusting either the power or time of ultrasonication. 47,48 In the canonical composition, 10 vol% of the total suspension volume was silicone oil (Φ 1 = 0.10), 33 vol% of the aqueous phase volume was PEGDA ( = 0.33), with the surfactant, Tween20, being at a concentration of 100 mM in the aqueous phase ( 20 = 100 mM). For nanoemulsions with this composition, average sizes measured by dynamic light scattering (DLS) range from approximately 30-400 nm depending on the ultrasonication power and processing time ( Figure 1b).…”

Asymmetric soft-hard colloidal mixtures: Osmotic effects, glassy states and rheology

“…Adding polymers to microgel glasses was also found to induce melting and eventual re-entrance AG formation, with the extension of the ergodic region depending on the microstructure of the particles (e.g., the crosslinking density) [7], [12], [15], [29], the size ratio and the potentially changing solvent quality for the polymer. Similarly to star polymers, slightly crosslinked microgels or nanoemulsions were found to de-swell in the presence of small linear polymers [30], [31], [32], [33], [34], [35], [36]. Along these lines, studies with food protein systems, which are also soft, confirmed the qualitative universality of this behavior [37].…”

Viscosity‐concentration relationships for nanodispersions based on glass transition point

“…When the inclusions are solid nanoparticles, the nanodispersions are called nanosuspensions. The industries where nanodispersions have a major presence include food, pharmaceutical, cosmetics, lubricants, paints, coatings, petroleum, polymer, agriculture, and electronics . For instance, a number of newly discovered drugs are water insoluble and therefore have poor bioavailability.…”