The origin of amphipathic nature of short and thin pristine carbon nanotubes - a fully recyclable 1D emulsion stabilizers for green chemistry applications

Short and thin pristine carbon nanotubes (CNTs) emerge as 1D emulsion stabilizers capable of replacing aquatoxic low-molecular surfactants. However, inconsistencies in understanding of water-solid interfaces for realistic CNTs hamper their individualization-driven functionalities, processability in benign media, and compatibility with a broad-scale of matrices. Pristine CNT processing based on water and inexpensive n-alkanes within a low energy regime would constitute an important step towards greener technologies. Therefore, we quantitatively assess structural CNT components, placing various CNTs on the scale from hydrophobicity to hydrophilicity. This structural interweave leads to amphipathicity enabling the formation of water-in-oil emulsions. Combining experiments with theoretical studies, we comprehensively characterize CNTs and CNT emulsions establishing descriptors of the emulsifying behavior of pristine and purified CNTs. They emerge as having hydrophilic open-ends, small number of oxygen-functionalized/vacancy surface areas, and hydrophobic sidewalls and full caps. The interplay of these regions allows short and thin CNTs to be utilized as fully recyclable 1D surfactants stabilizing water/oil emulsions which, as we demonstrate, can be applied as paints for flexible conductive coatings. We also show that their amphipathic strength depends on CNT size, the pristine-to-oxidized/vacancy domains and the oil-to-water ratios.