Formation and stability of nanoemulsions with mixed ionic–nonionic surfactants

Abstract

A simple, low-energy two-step dilution process has been applied with binary mixtures of ionic-nonionic surfactants to prepare nanoemulsions. The systems consist of water/DDAB-C(12)E(5)/decane. Nanoemulsions were obtained by dilution of concentrates located in bicontinuous microemulsion or lamellar liquid crystal phase regions. The nanoemulsions generated were investigated both by contrast-variation small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS profiles show that C(12)E(5) nanodroplets suffer essentially no structural change on incorporation of the cationic DDAB surfactant, except for increased electrostatic repulsive interactions. Interestingly, SANS indicated that the preferred droplet sizes were hardly affected by the surfactant mixture composition (up to a DDAB molar ratio (m(DDAB)/(m(DDAB) + m(C(12)E(5))) of 0.40) and droplet volume fraction, phi, between 0.006 and 0.120. No notable changes in the structure or radius of nanoemulsion droplets were observed by SANS over the test period of 1 d, although the droplet number intensity decreased significantly in systems stabilized by C(12)E(5) only. However, the DLS sizing shows a marked increase with time, with higher droplet volume fractions giving rise to the largest changes. The discrepancy between apparent nanoemulsion droplet size determined by DLS and SANS data can be attributed to long-range droplet interactions occurring outside of the SANS sensitivity range. The combined SANS and DLS results suggest flocculation is the main mechanism of instability for these nanoemulsions. The flocculation rate is shown to be significantly retarded by addition of the charged DDAB, which may be due to enhanced electrostatic repulsive forces between droplets, leading to improved stability of the nanoemulsions.

The use of Brazilian vegetable oils in nanoemulsions: an update on preparation and biological applications

“…NE represent a class of emulsions with a diameter of less than one micrometer (50-200 nm), low viscosity droplet, transparent or translucent appearance with intense bluish reflection or milky, depending on the size of the droplets (Constantinides, Chaubal, Shorr, 2008;Wang et al, 2009;Calderó, García-Celma, Solans, 2011;Gupta et al, 2016;Hörmann, Zimmer et al, 2016). Frequently, NE are called ultrafine or submicrometric emulsion and mini-emulsions.…”

“…These systems are fragile by nature and are usually very transparent and fluid, the slightest sign of destabilization becomes readily visible (Sonneville-Aubrun, Simonnet, L'alloret, 2004). As to composition, NE are oil-in-water (O/W) emulsions containing 10 to 20% oil stabilized with 0.5 to 2% surfactant and the active ingredients are preferably solubilized, dispersed and/or adsorbed onto the internal phase of the nanostructure (Wang et al, 2009;Calderó, García-Celma, Solans, 2011;Wang et al, 2009;Calderó, García-Celma, Solans, 2011;Garg, Kokkoli, 2005;Maestro et al, 2008;Spinelli et al, 2010). The NE are kinetically stable due to their steric balance, especially when formulated with nonionic surfactants Gupta et al, 2016).…”

Nanoemulsion stability: Experimental evaluation of the flocculation rate from turbidity measurements

“…It was also noticed that the droplets become highly adhesive at high salinity exhibiting large contact angles. According to Wang et al [117], flocculation is the main mechanism of destabilization in water/decane emulsions stabilized with a mixture of pentaoxyethylene lauryl ether (C 12 E 5 ) and di-dodecyldimethylammonium bromide.…”

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“…NEs are characterized by various techniques such as viscosity determination 1, 4, 9, 11 small-angle neutron scattering (SANS) 17 , Transmission Electron Microscopy (TEM) 4,9,[11][12] , Zeta Potential 4, 11-12 Scanning Electron Microscope (SEM) 12 and Dynamic Light Scattering (DLS) 1,12,17 . Basedon ongoing studies of these techniques, the following properties of NEs have been visualized.…”