The Pristine Oil/Water Interface: Surfactant‐Free Hydroxide‐Charged Emulsions

Abstract

Emulsionen von Öl in Wasser sind in alkalischer Lösung auch ohne Tenside stabil. Die durch Anlagerung von Hydroxidionen erzeugte Oberflächenladungsdichte (siehe Bild) bestimmt man aus der elektroakustisch ermittelten Tröpfchengröße und der Menge an NaOH, die benötigt wird, um den pH‐Wert während der Homogenisierung konstant zu halten.

Hydroxide and hydronium ion adsorption — A survey

“…Numerous experimental studies have revealed that inert surfaces show a negative surface charge in neutral solutions and isoelectric points (IEP) close to pH 4. Similar characteristics were observed in experiments with oil/water [10][11][12][13][14] and gas/water [15][16][17][18][19][20] interfaces.…”

“…Although the majority of integral experiments suggest a preferential adsorption of hydroxide ions [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], an opposite picture has emerged from experiments analyzing molecular structures and MD simulations [21•-26]. These studies concluded that the concentration of hydronium ions, but not hydroxide ions, is enhanced at the gas/water interface [21•-26].…”

“…In MD simulations, ion concentrations of 0.1 M or higher are typically used [23][24][25][26], which restricts the conditions to either high or very low pH values. In contrast to this, the majority of the integral experimental studies [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] are performed at intermediate pH values (pH 2-11) in solutions of ionic strength lower than 0.1 M. Below we provide an overview of results obtained for the different types of interfaces. Special emphasis is placed on solid/water interfaces.…”

Consequences of shifted ion adsorption equilibria due to nonelectrostatic interaction potentials in electrical double layers

“…High or low pH could be expected to increase not only the deprotonation or protonation of acid and base groups, respectively, at the oil interface but also their site densities due to preferential migration from the oil bulk to the surface and reorientation there. Further, surprisingly large negative at high pH are observed for a wide range of nonpolar phases (air, oils and hydrophobic polymers) in 1:1 electrolytes [35,66,67]. Preferential adsorption of hydroxide ions is believed to be the cause, and may operate at crude oil interfaces, reinforced by hydroxide affinity for acidic groups on asphaltenes and resins.…”

Autonomous Self‐Assembly of Ionic Nanoparticles into Hexagonally Close‐Packed Lattices at a Planar Oil–Water Interface

“…Although alcohol seems to have a dominant effect on the self-assembly, it is also known that oil in contact with water acquires a negative net charge due to accumulation of hydroxide anions. [10] So, the role of the attractive electrostatic forces between oppositely charged interface and the NPs in formation of well-ordered NP arrays should not be excluded.…”