Jul 7, 2009
Tunable interactions between nanotubes and polymer put to work
A composite composed of multi-walled carbon nanotubes (MWCNTs) and pyrene-derivated hydrolyzed poly(styrene-co-maleic anhydride) (pyrene-HSMA) shows tunable fluorescence that is sensitive to pH, temperature and solvents. The behaviour can be exploited to highlight changes in polymer conformation and to expose polymer-MWCNT interactions.
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.
About the author
The work was performed in the Organic Semiconductors Lab at Zhejiang University, China. Yan Gao is a PhD candidate studying materials science. Dr Minmin Shi is an associate professor. Dr Chaohua Xue is currently an associate professor at Shanxi Scientific and Technical University, China. Mr Renjia Zhou was a Masters student at the lab, and is now a PhD candidate at the University of Florida, US. Prof. Mang Wang was founder of the Lab and is now retired. Prof. Hongzheng Chen is head of the Lab.