Stable pickering emulsions using multi-walled carbon nanotubes of varying wettability

The influence of surface functional groups on multi-walled carbon nanotubes (MWNT) the stability and type of Pickering emulsions in water and oil systems is reported. The strong interaction between carbon nanotubes allows for the unique ability to tune emulsion type and droplet size while producing emulsions that are stable for over a month. This behavior stands in stark contrast to what is known for other Pickering emulsion stabilizers such as colloidal silica. Emulsion droplet size displays parabolic behavior, with amphiphilic MWNTs stabilizing the smallest emulsion droplets while larger droplets are stabilized with more hydrophobic or hydrophilic MWNTs. At equivalent volumes of oil and water, water-in-oil emulsions are stabilized by hydrophobic MWNTs, while hydrophilic MWNTs result in oil-in-water emulsions. Emulsion droplet size and type vary depending on the wettability of the MWNTs when changing the oil-to-water ratio. Mixing MWNTs of different wettability results in a non-linear emulsion droplet size trend and may possibly be due to the interaction between the MWNTs of different wettability. To our knowledge, no other Pickering emulsion stabilizer allows for this range of tuning of emulsion properties while sustaining high emulsion stability, even when changing the oil-to-water ratio to induce catastrophic emulsion inversion.