Novel Oil‐in‐Water Emulsions Stabilised by Ionic Surfactant and Similarly Charged Nanoparticles at Very Low Concentrations

Abstract

Novel oil-in-water (O/W) emulsions are prepared which are stabilised by ac ationic surfactant in combination with similarly charged alumina nanoparticles at concentrations as low as 10 À5 m and 10 À4 wt %, respectively.T he surfactant molecules adsorb at the oil-water interface to reduce the interfacial tension and endowd roplets with charge ensuring electrical repulsion between them, whereas the charged particles are dispersed in the aqueous films between droplets retaining thickl amellae,r educing water drainage and hindering flocculation and coalescence of droplets.This stabilization mechanism is universal as it occurs with different oils (alkanes, aromatic hydrocarbons and triglycerides) and in mixtures of anionic surfactant and negatively charged nanoparticles. Further,s uch emulsions can be switched between stable and unstable by addition of an equimolar amount of oppositely charged surfactant whichf orms ion pairs with the original surfactant destroying the repulsion between droplets.

Conversion of bile salts from inferior emulsifier to efficient smart emulsifier assisted by negatively charged nanoparticles at low concentrations

“…We note that some Pickering emulsions can also be stabilized when the interfacial coverage by particles is quite low. [36,37] Here, we believe that only NaDC molecules adsorb at the oil-water interface with silica particles dispersed in the continuous phase between droplets [31][32][33][34][35] producing an oil-indispersion emulsion [35] as shown by the SEM and fluorescence microscopy images (Figures 2 and S7). It was further observed that this strategy of improving the emulsifying ability of BS by addition of silica particles is universal for other BS.…”

“…The fluorescence image (particles labelled green in Figure S7) also proves the position of the particles is mainly in the aqueous continuous phase. [31][32][33][34][35] This microstructure is different from that of Pickering emulsions stabilized by NaDC and positively charged alumina nanoparticles (Figure 2d), in which particles attach to the oilwater borders forming winkled films on the surfaces of dried oil droplets. We note that some Pickering emulsions can also be stabilized when the interfacial coverage by particles is quite low.…”

“…In addition, the concentrations of NaDC and silica particles required for stabilization of the emulsions are extremely low, and the synergistic effects between NaDC and particles can be triggered by CO 2 /N 2 , yielding switchable oil-in-dispersion emulsions. [31]…”

Stabilization of a Highly Concentrated Colloidal Suspension of Pristine Metallic Nanoparticles

“…4. The initial velocities were set for copper atoms that were consistent with the temperature of (300 K) 5. Then another 500000 steps of equilibration were performed in the NPT.…”

“…It is well known that the former is stabilized in the colloids due to steric forces because of the presence of the capping agent. On the other hand, the uncapped NPs are electrostatically stabilized due to the native surfaces [4][5][6] . Although the capping agents help in the steric stabilization of the NPs in liquids, they reduce the direct interaction of NPs with each other as well as the space for preferential adsorptions of ions/molecules on the surfaces of the NPs.…”