Ion Valence and Concentration Effects on the Interaction between Polystyrene Sulfonate-Modified Carbon Nanotubes in Water

Abstract

We use molecular dynamics simulations and the adaptive biasing force method to evaluate the potential of mean force between two carbon nanotubes (CNTs), with each surface modified by an adsorbed sodium-polystyrene sulfonate (Na-PSS) polyanion, in aqueous electrolyte media. Changes in the electrolyte concentration and counter-ion valence can lead to qualitative changes in the interactions between polyelectrolyte-modified CNTs. We show that in the presence of monovalent NaCl salt, a long-range screened electrostatic repulsion exists between CNTs. This repulsion can be described by a generalized Derjaguin− Landau−Verwey−Overbeek interaction that accounts for anisotropy of charged cylindrical colloids. In contrast, an attraction between CNTs is observed in the presence of divalent MgCl 2 salt. The attraction is attributed to ion-pair correlations between anionic SO 3 − groups, on different PSS chains, induced by Mg 2+ counter ions acting as bridges between the SO 3 − groups. However, in the salt-free case where divalent Mg 2+ counter ions are considered instead of the Na + counter ions, condensation of Mg 2+ counter ions on the adsorbed PSS chain results in the neutralization of surface charge and leads to a short-range steric repulsion between the CNTs. Thus, our simulations show that qualitatively different interactions, either short-range steric repulsion, long-range repulsion or attraction, can arise between PSS-modified CNTs based on counterion valence and electrolyte concentration.

The influence of silica nanoparticle geometry on the interfacial interactions of organic molecules: a molecular dynamics study

“…However, with the addition of 0.5 M NaCl electrolyte, the surface potential on the cuboid silica has decreased to approximately 0.1 V, as a result of enhanced screening of its surface charge by the condensation of Na + counter-ions. This result is consistent with the idea of electrostatic screening of the surface potential with the addition of salt 42 and consequently, a decrease in the screening length so-called Debye length. The surface potentials observed with respect to spheroid and cuboid geometry at other pH conditions can be seen in Fig.…”

Electrical conductivity of poly(vinyl alcohol)/carbon nanotube multilayer thin films: Influence of sodium polystyrene sulfonate mediated carbon nanotube dispersion

“…Thus, the results obtained from our simulations are in qualitative agreement with our experimental observations of large negative zeta potentials on PSS-modified MWCNT surfaces. The experimental results are also in agreement with our recent atomistic simulation studies [44] on interactions between two CNT/Na-PSS complexes in water, where we explicitly showed using free energy calculations that the negative potential leads to a long-range repulsive interaction energy between two Na-PSS modified CNT. Further, we have also demonstrated that addition of an electrolyte leads to a screening of the electrostatic interaction between the two CNT/Na-PSS complexes.…”

“…[ 43 ] A detailed description of the simulation setup and calculations can be found in our recent simulation work investigating ionic effects on the stability of Na‐PSS‐modified CNT dispersions. [ 44 ]…”

“…[43] A detailed description of the simulation setup and calculations can be found in our recent simulation work investigating ionic effects on the stability of Na-PSS-modified CNT dispersions. [44] 3 | RESULTS AND DISCUSSION concentration was varied. These dispersions are ultrasonicated with different time intervals and the corresponding photographic images of these dispersions are shown in Figure 1.…”

Tunable Energy Barrier for Intercalation of a Carbon Nanotube into Graphene Nanosheets: A Molecular Dynamics Study of a Hybrid Self-Assembly

“…The CHARMM force field was used to model all interatomic interactions, and the TIP3P model was used to describe water molecules. The detailed description of the simulation setup and the method adopted are provided in the Supporting Information of Section S1, and the same information discussed extensively can be found in publications from our group. − …”