Christian Punckt - Dispersion Stability of Functionalized Graphene in Aqueous Sodium Dodecyl Sulfate Solutions

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  Hsieh, Andrew G., Korkut, Sibel, Punckt, Christian, Aksay, Ilhan   A. 29 14831-14838-

  Abstract: The colloidal stability of   functionalized graphene sheets (FGSs) in aqueous sodium dodecyl   sulfate (SDS) solutions of different concentrations was studied   by optical microscopy and ultraviolet visible light absorption   after first dispersing the FGSs ultrasonically. In up to similar   to 10 mu M SDS solutions, FGSs reaggregated within a few minutes,   forming ramified structures in the absence of SDS and   increasingly compact structures as the amount of SDS increased.   Above similar to 10 mu M, the rate of reaggregation decreased   with increasing SDS concentration; above similar to 40 mu M, the   suspensions were colloidally stable for over a year. The   concentration of similar to 40 mu M SDS lies 2 orders of   magnitude below the critical surface aggregation concentration of   similar to 1.8 mM SDS on FGSs but above the concentration   (similar to 18 mu M) at which SDS begins to form a monolayer on   FGSs. Neither surface micelle nor dense monolayer coverage is   therefore required to obtain stable aqueous FGS dispersions. We   support our experimental results by calculating the van der Waals   and electrostatic interaction energies between FGSs as a function   of SDS concentration and show that the experimentally observed   transition from an unstable to a stable dispersion correlates   with a transition from negative to positive interaction energies   between FGSs in the aggregated state. Furthermore, our   calculations support experimental evidence that aggregates tend   to develop a compact structure over time.

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