Correlation between specific ion adsorption at the air/water interface and long–range interactions in colloidal systems

Abstract

Specific ion effects are of high impact in colloid science and dominate processes in aqueous systems from protein folding or precipitation to ordering of particles or macromolecules in bulk solutions. Due to the large internal interface of colloidal systems especially interfacial ion effects are of importance. This paper presents a new insight into the specific ion effects at the air/water interface of monovalent electrolyte solutions and their consequences for long-range interactions in colloidal systems. Solely, in an asymmetric film (i.e. wetting film) one can determine the sign and precise value of the surface potential of the free air/water surface. It is shown that the all over charges of the interfacial region, which are affected by the type of ion, dominate the interfacial forces even over several tens of nm. This is of interest for tailoring the stability of colloidal systems. It is clearly shown that the air/water interface is negatively charged and that both anions and cations affect the surface potential even at very low electrolyte concentrations (10 À4 M).

Effect of polyelectrolytes on (de)stability of liquid foam films

“…The electrostatic stabilization is explained by negative charges at the air-water interface resulting from OH À adsorption. 8,39,40 Aer the addition of 5 Â 10 À3 monoM PDADMAC a CBF to NBF transition is already induced at low pressures at about 800 Pa. In this state the lm is only a few nm thick.…”

Long-range specific ion-ion interactions in hydrogen-bonded liquid films

“…[1][2][3] Action potentials, osmotic flows, energy transduction, 4 and the stabilization of proteins are driven by ion concentration gradients across liquid films on hydrophobic biomaterials. 3,[5][6][7][8][9][10] Recent experiments in our laboratory revealed that ions interact specifically at the prototype airwater interface over separations that vastly exceed the range of direct electrostatic forces in any dielectric medium. 11 Such long-range specific ion effects (LR-SIE) may be triggered by electrostatic and electrodynamic forces, but it is obvious that they must be powered by other mechanisms, such as the thermal fluctuations intrinsic to fluid interfaces.…”

Hofmeister effects in micromolar electrolyte solutions

“…[1][2][3][4] Specific ion adsorption at the surface of the ocean is reflected in the distinct composition of marine aerosols [5][6][7][8] and its significant impact on the chemistry of the atmospheric boundary layer. 5,[9][10][11][12][13][14] Enzyme activities, 15 protein binding, 16 and self-assembly processes in general [17][18][19][20][21][22] also show pronounced specific ion effects (SIE). Controlling the self-aggregation of nanoparticles and biopolymers via SIE is a tantalizing goal that calls for a deeper understanding of structural, Coulombic, and non-electrostatic effects at low, intermediate, and high concentrations.…”