Surfactant solutions as reservoirs for large amounts of carbonaceous particles

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Abstract
Despite their hazardous nature, carbonaceous particles (CPs) own very appealing properties, which make them a leading material in numerous applications. A systematic work on the properties of aqueous dispersions containing CPs, cetylpyridinium chloride (CPyCl), and sodium salicylate (NaSal) is here presented. Being CPs not soluble in water, an effective preparation method to obtain stable and homogeneous solutions was developed. Furthermore, a full characterization of the systems was performed by means of UV-Visible absorption spectroscopy, rheology, and interfacial tension measurements. Hydrophobic CPs are hard to disperse in a water matrix. The adoption of CPyCl as solubility enhancer was a sound strategy to finely disperse high concentration of CPs in an aqueous environment. The high CPs concentration involved conferred to the solutions a dark color and peculiar properties, such as UV and visible light radiation absorbance. The addition of NaSal to the CPyCl-CPs water solutions donated to the system robust viscoelasticity. We investigated 100 mM CPyCl aqueous solutions, with 60 and 70 mM NaSal, containing various amounts of CPs (0–9500 ppm). CPs at concentrations beneath 9500 ppm do not influence the system rheological properties. The well-known effect of NaSal on CPyCl solutions remains unaltered even in the presence of CPs at concentrations below 9500 ppm. On the other hand, the addition of 9500 ppm CPs provokes a moderate change in the rheological properties and microstructure of the systems. At a such high concentration, CPs seem to mimic the effect of NaSal on the micellar solutions, acting as a full-fledged hydrophobic salt.

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