The Hydration Repulsion between Charged Surfaces as an Interplay of Volume Exclusion and Dielectric Saturation Effects
✍ Scribed by V.N. Paunov; R.I. Dimova; P.A. Kralchevsky; G. Broze; A. Mehreteab
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 228 KB
- Volume
- 182
- Category
- Article
- ISSN
- 0021-9797
No coin nor oath required. For personal study only.
✦ Synopsis
Israelachvili et al. (2,
and Pashley (4, 5), who examined We demonstrate that the hydration repulsion between smooth the validity of DLVO theory at small film thicknesses in expericharged surfaces can be attributed to the interplay of two effects ments with films from aqueous electrolyte solutions confined which are not taken into account in the conventional DLVO thebetween two mica surfaces. At electrolyte concentrations below ory. These are the finite size of the counterions and the variable 10 04 M (KNO 3 or KCl) they observed the typical DLVO dielectric permittivity across the electric double layers. We involve maximum. However, at electrolyte concentrations higher than these two effects in the theory by coupling the Poisson-Boltzmann 10 03 M they did not observe the expected DLVO maximum equation with the Bikerman and Booth equations. The resulting and primary minimum; instead a strong short-range repulsion nonlinear ordinary differential equation of second order is solved was detected, see also Ref. (6). Empirically, this force called numerically. The theory is applied to interpret available experimental data for the dependence of the surface force on the distance the ''hydration repulsion'' appears to follow an exponential measured by means of the surface force apparatus. Excellent law (6) agreement between theory and experiment is obtained with reasonable values of the two adjustable parameters: the area per surface f hydr (h) Å f 0 e 0 h / l 0 , [1.1] charge and the counterion adsorption energy. It turns out that the contribution of the ionic-excluded volume to the hydration force
where the decay length l 0 É 0.6-1.1 nm for 1:1 electrolytes is several times greater than the contribution due to the dielectric and f 0 depends on the hydration of the surfaces but is usually saturation. The developed theoretical approach can find applicain the range of 3-30 mJ/m 2 .
tion for interpreting data about the interactions in aqueous thin films, colloidal dispersions, and micellar surfactant solutions in
The physical importance of the hydration force is that it the presence of electrolyte at ionic strengths above 1 m M. ᭧ 1996 stabilizes some dispersions preventing coagulation in the Academic Press, Inc.
primary DLVO minimum. It is believed that the hydration Key Words: counterion adsorption; dielectric saturation; hydraforce is connected with the binding of strongly hydrated tion energy of ions; hydration repulsion; surface force apparatus; ions at the interface. This is probably the explanation of the volume exclusion effect for ions.
experimental results of Healy et al. (7), who found that even high electrolyte concentrations cannot cause coagulation of amphoteric latex particles due to binding of strongly hy-''Numerical Recipes in FORTRAN,'' second ed. Cambridge Univ. Press, Cambridge, 1992. w(x) and w(x).