Diameter- and metallicity-selective enrichment of single- walled carbon nanotubes using polymethacrylates with pendant aromatic functional groups

Current methods for the synthesis of single-walled nanotubes (SWNTs) produce mixtures of semiconducting (sem-) and metallic (met-) nanotubes. Most approaches to the chemical separation of sem-/met-SWNTs are based on small neutral molecules or conjugated aromatic polymers, which characteristically have low separation/dispersion efficiencies or present difficulties in the postseparation removal of the polymer so that the resulting field-effect transistors (FETs) have poor performance. In this Full Paper, the use of three polymethacrylates with different pendant aromatic functional groups to separate cobalt-molybdenum catalyst (CoMoCAT) SWNTs according to their metallicity and diameters is reported. UV/Vis/NIR spectroscopy indicates that poly(methyl-methacrylate-co-fluoresceino- acrylate) (PMMAFA) and poly(9-anthracenylmethyl-methacrylate) (PAMMA) preferentially disperse semiconducting SWNTs while poly- (2-naphthylmethacrylate) (PNMA) preferentially disperses metallic SWNTs, all in dimethylforamide (DMF). Photoluminescence excitation (PLE) spectroscopy indicates that all three polymers preferentially disperse smaller-diameter SWNTs, particularly those of (6,5) chirality, in DMF. When chloroform is used instead of DMF, the larger-diameter SWNTs (8,4) and (7,6) are instead selected by PNMA. The solvent effects suggest that diameter selectivity and change of polymer conformation is probably responsible. Change of the polymer fluorescence upon interaction with SWNTs indicates that metallicity selectivity presumably results from the photon-induced dipole-dipole interaction between polymeric chromophore and SWNTs. Thin-film FET devices using semiconductor-enriched solution with PMMAFA have been successfully fabricated and the device performance confirms the sem-SWNTs enrichment with a highly reproducible on/off ratio of about 103.