Binding Affinities and Thermodynamics of NoncovalentFunctionalization of CarbonNanotubes with Surfactants.

Binding affinity and thermodynamicunderstanding between a surfactantand carbon nanotube is essential to develop various carbon nanotubeapplications. Flavin mononucleotide-wrapped carbon nanotubes showinga large redshift in optical signature were utilized to determine thebinding affinity and related thermodynamic parameters of 12 differentnanotube chiralities upon exchange with other surfactants. Determinedfrom the midpoint of sigmoidal transition, the equilibrium constant(K), which is inversely proportional to the bindingaffinity of the initial surfactant-carbon nanotube, provided quantitativebinding strengths of surfactants as SDBS > SC ≈ FMN >SDS,irrespective of electronic types of SWNTs. Binding affinity of metallictubes is weaker than that of semiconducting tubes. The complex Kpatterns from semiconducting tubes show preference tocertain SWNT chiralities and surfactant-specific cooperativity accordingto nanotube chirality. Controlling temperature was effective to modulate Kvalues by 30% and enables us to probe thermodynamic parameters.Equally signed enthalpy and entropy changes produce Gibbs energy changeswith a magnitude of a few kJ/mol. A greater negative Gibbs energyupon exchange of surfactant produces an enhanced nanotube photoluminescence,implying the importance of understanding thermodynamics for designingnanotube separation and supramolecular assembly of surfactant. [ABSTRACT FROM AUTHOR]