Solvent-induced ion clusters generate long-ranged double-layer forces at high ionic strengths
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| Název: | Solvent-induced ion clusters generate long-ranged double-layer forces at high ionic strengths |
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| Autoři: | Ribar, David, Woodward, Clifford E., Forsman, Jan |
| Přispěvatelé: | Lund University, Faculty of Science, Department of Chemistry, Physical and theoretical chemistry, Computational Chemistry, Lunds universitet, Naturvetenskapliga fakulteten, Kemiska institutionen, Enheten för fysikalisk och teoretisk kemi, Beräkningskemi, Originator |
| Zdroj: | Soft Matter. 21(27):5562-5572 |
| Témata: | Natural Sciences, Chemical Sciences, Physical Chemistry (including Surface- and Colloid Chemistry), Naturvetenskap, Kemi, Fysikalisk kemi (Här ingår: Yt- och kolloidkemi) |
| Popis: | Recent experimental results by the surface force apparatus (SFA) have identified a dramatic deviation from previously established theories of simple electrolytes. This deviation, referred to as anomalous underscreening, suggests that the range of electrostatic interactions increase upon a further addition of salt, beyond some threshold concentration (usually about 1 M). In this theoretical work, we explore an extension of the restricted primitive model (RPM) wherein a short-ranged pair potential of mean force (sPMF) is added to the usual Coulombic interactions so as to mimic changes of the hydration as two ions approach one another. The strength of this potential is adjusted so that the modified RPM saturates at a realistic concentration level (within a range 4-7 M, typical to aqueous 1 : 1 salts). We utilise grand canonical simulations to establish surface forces predicted by the model and compare them directly with SFA data. We explore different sPMF models, which in all cases display significant clusteringat concentrations above about 1 M. In these models, we find significant double-layer repulsion at separations that significantly exceed those expected from standard RPM predictions. We do not, however, observe an increase of the screening length with salt concentration, but rather that this screening length seemingly saturates at a (rather high) value. The simulated long-ranged interactions are shown to correlate with ion cluster formation, implicating the important role of accompanying cluster-cluster interactions. In particular, steric interactions between clusters (manifested in density-density correlations) are quite relevant in these systems. |
| Přístupová URL adresa: | https://doi.org/10.1039/d5sm00027k |
| Databáze: | SwePub |
Nájsť tento článok vo Web of Science | Abstrakt: | Recent experimental results by the surface force apparatus (SFA) have identified a dramatic deviation from previously established theories of simple electrolytes. This deviation, referred to as anomalous underscreening, suggests that the range of electrostatic interactions increase upon a further addition of salt, beyond some threshold concentration (usually about 1 M). In this theoretical work, we explore an extension of the restricted primitive model (RPM) wherein a short-ranged pair potential of mean force (sPMF) is added to the usual Coulombic interactions so as to mimic changes of the hydration as two ions approach one another. The strength of this potential is adjusted so that the modified RPM saturates at a realistic concentration level (within a range 4-7 M, typical to aqueous 1 : 1 salts). We utilise grand canonical simulations to establish surface forces predicted by the model and compare them directly with SFA data. We explore different sPMF models, which in all cases display significant clusteringat concentrations above about 1 M. In these models, we find significant double-layer repulsion at separations that significantly exceed those expected from standard RPM predictions. We do not, however, observe an increase of the screening length with salt concentration, but rather that this screening length seemingly saturates at a (rather high) value. The simulated long-ranged interactions are shown to correlate with ion cluster formation, implicating the important role of accompanying cluster-cluster interactions. In particular, steric interactions between clusters (manifested in density-density correlations) are quite relevant in these systems. |
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| ISSN: | 1744683X 17446848 |
| DOI: | 10.1039/d5sm00027k |