Molecular Simulation of Electrolyte-Induced Interfacial Interaction between SDS/Graphene Assemblies
B Wu and XN Yang, JOURNAL OF PHYSICAL CHEMISTRY C, 117, 23216-23223 (2013).
The interaction between surfactant-coated graphenes plays a critical role in the performance of surfactant-stabilized graphene dispersion. Herein, we quantified the interaction by simulating the potential of mean force (PMF) between two graphenes encapsulated in sodium dodecyl sulfate (SDS) surfactant micelles. It is observed that adsorbed SDS surfactants produce a long-range free energy barrier, hindering the aggregation of graphenes. Both increasing surfactant coverage and introducing electrolyte (CaCl2) can lead to an enhanced repulsive nature of PMF. Through splitting the total PMF into various contributions, the precise interaction mechanism of graphenes in aqueous SDS environment has been demonstrated. Furthermore, our result reveals the role of electrolyte ions in the modifying the interaction between the SDS/graphene assemblies, which cannot be accounted for by the traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. This result might show a possible microscopic evidence or explanation on the recently reported experiments. Additionally, a further analysis for SDS self-assembly morphology on graphene surface was used to explain the molecular origin of the electrolyte-induced structure transformation. The salt bridges formed between electrolyte cations and surfactants anions are confirmed to cause the structure change in the SDS/graphene assembly. This work provides a correlation analysis between the supramolecular self-assembly nanostructure and the interfacial interaction.
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