Many reagents have been employed to improve the solubility or compatibility of carbon nanotubes in different media. Among these, pyrene derivatives are one of the most frequently adopted chemicals for their strong attachment to the sidewalls of carbon nanotubes through π–π stacking. However, the tunable interactions between carbon nanotubes and pyrene derivatives under external stimuli are often ignored.

Scientists in China have used pyrene-derivatized hydrolyzed poly(styrene-co-maleic anhydride) (pyrene–HSMA) to modify the surface of MWCNTs. The resulting composite, MWCNTs/pyrene–HSMA, exhibits good solubility in water, polar solvents (DMF, ethanol and THF), and mixed solvents (water/ethanol and water/THF). In addition, the team has shown that the composite's fluorescent behaviour can be used as a probe to estimate polymer-MWCNT interactions at different pH values, temperatures and in various solvents.

The maximum fluorescence intensity of the composite in water was found at pH=7. Above or below this pH value, the extended polymer coils in water would collapse due to the decreased intrachain repulsive interactions and facilitate fluorescence quenching (through energy transfer from pyrene moieties to MWCNTs) leading to a reduction in the intensity of the emission. Similar phenomena were also observed when varying temperatures and solvents. The behaviour may provide the basis for a multifunctional sensor and help researchers to understand the properties of modified CNTs in more detail.

The researchers presented their work in Nanotechnology.