| 1. |
- Thuresson, Axel, et al.
(författare)
-
Interaction and Aggregation of Charged Platelets in Electrolyte Solutions: A Coarse-Graining Approach.
- 2014
-
Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:26, s. 7405-7413
-
Tidskriftsartikel (refereegranskat)abstract
- A coarse-graining approach has been developed to replace the effect of explicit ions with an effective pair potential between charged sites in anisotropic colloidal particles by optimizing a potential of mean force against the results of simulations of two such colloidal particles with all ions in a cell model. More specifically, effective pair potentials were obtained for charged platelets in electrolyte solutions by simulating two rotating parallel platelets with ions at the primitive model level, enclosed in a cylindrical cell. One-component bulk simulations of many platelets interacting via the effective pair potentials are in excellent agreement with the corresponding bulk simulations with all mobile charges present. The bulk simulations were mainly used to study the effects of platelet size, flexibility, and surface charge density on platelet aggregation in an aqueous 2:1 electrolyte, but systems in a 1:1 electrolyte were also investigated.
|
|
| 2. |
- Thuresson, Axel, et al.
(författare)
-
Monte carlo simulations of parallel charged platelets as an approach to tactoid formation in clay.
- 2013
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:29, s. 9216-9223
-
Tidskriftsartikel (refereegranskat)abstract
- The free energy of interaction between parallel charged platelets with divalent counterions has been calculated using Monte Carlo simulations to investigate the electrostatic effects on aggregation. The platelets are primarily intended to represent clay particles. With divalent counterions, the free energy for two platelets or two tactoids (clusters of parallel platelets) shows a minimum at a short separation due to the attraction caused by ion-ion correlations. In a salt-free system, the free energy of interaction has a long-range repulsive tail beyond the minimum. The repulsion increases for tactoids with larger aggregation numbers, whereas the depth of the free-energy minimum is gradually reduced. For large enough aggregation numbers, the repulsion is dominating and the minimum is no longer a global free-energy minimum. This is an effect of the depletion of counterions free in solution (outside tactoids) as counterions and platelets aggregate into tactoids and the resulting redistribution of counterions in the system changes the effective interactions between platelets and tactoids. The difference in tactoid-tactoid interactions as a function of aggregation number can be removed by adding enough salt to mask the depletion. Adding salt also reduces the repulsive tail of the free energy of interaction and enhances the minimum. No dependence on the aggregation number suggests that an isodesmic model with a monotonically decaying distribution of aggregation numbers can be used to describe a clay system. This may help to explain the experimental observations of low average numbers of platelets in tactoids, although factors not included in the simulation model may also play an important role.
|
|
