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The principle mechanism of the electrostatic interaction between colloids in water.




M. Hishida, Y. Nomura, R. Akiyama, Y. Yamamura, K. Saito, Phys. Rev. E, 96, 040601 (2017).

Dispersion and aggregation of colloids have been discussed by the balance of electric double layer force and van der Waals force (DLVO theory). The DLVO theory predicts that the electric double layer force depends on the ionic strength in the solution. In other words, the equilibrium distance between the colloids is also expected to be determined by the ionic strength. On the other hand, we have measured the equilibrium interlayer distances of anionic phospholipid bilayers in three electrolyte solutions with different valences of the cations using small angle X-ray scattering and found that the experimental results do not agree with this prediction.


In general, the ionic concentrations of the colloidal aggregated phase and bulk phases can be calculated approximately by Gibbs-Donnan equilibrium. When the ion concentrations were calculated in the present case, it was calculated that most of the added ions, both counterions and co-ions, were released from the aqueous phase between the bilayers into the bulk phase. This state differs significantly from the ion distribution that has been considered when calculating the electric double layer force in DLVO theory. Under the heterogeneous distribution of ions calculated here, the electric double layer force will be different from the classical one used in DLVO theory, and will be the sum of the osmotic pressure generated by the heterogeneous distribution of ions and the repulsive force of the remaining counterions to maintain electrical neutrality between the membranes. The osmotic pressure acts as an attractive force between the membranes. The experimental results obtained in this study can be explained very well by using this equation. It was also found that the van der Waals force is sufficiently weak compared to the osmotic pressure that it is almost negligible.


M. Hishida, Y. Nomura, R. Akiyama, Y. Yamamura, K. Saito, Phys. Rev. E, 96, 040601 (2017).

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