In-situ synthesis of soluble poly(3-hexylthiophene)/multiwalled carbon nanotube composite: morphology, structure, and conductivity

Abstract

Soluble poly(3-hexylthiophene) (P3HT)-multiwalled carbon nanotube (MWNT) nanocomposites (PCNCs) are prepared by the in-situ oxidative polymerization of 3-hexylthiophene (3HT) in a dispersion of MWNT in CHCl₃. The MWNT-P3HT nanocomposite produces blackish-brown solution in chloroform, making it an easily processable system. With increase in MWNT concentration the molecular weight of P3HT has increased, but at higher MWNT concentration (8% w/w) the molecular weight has decreased. The head-tail (H-T) regioregularity of the samples remains the same with that of pure P3HT. The TEM pictures of PCNC-1 and PCNC-8 [the number indicates percentage (w/w) of MWNT with respect to monomer in the composite] show uniform wrapping of MWNT with P3HT. The increase of outer diameter in wrapped MWNT decreases with increase in MWNT concentration, but the PCNC-2.5 exhibits phase segregation by the formation of separate spheroid-like species on the partially wrapped MWNT surface. The higher molecular weight P3HT produced in the PCNC-2.5 has been attributed to this difference in morphology. Type 1 P3HT crystal is formed in all the PCNCs, and melting temperature shows an increase with increasing MWNT concentration except for the PCNC-2.5 sample. The glass transition temperature (T_g) remains unchanged in the PCNCs, but the β-transition temperature (T_β) varies differently in the different PCNCs. The storage modulus of PCNCs has increased abruptly (maximum increase 158%) in the PCNCs than that of pure P3HT. The UV-vis spectra of PCNCs show a red shift in the π-π∗ transition band while the emission spectra show a small blue shift with increase in MWNT concentration. Fluorescence quenching occurs in the PCNCs, and it increases with increase in MWNT concentration except for the PCNC2.5 sample. The conductivity values of both undoped and doped PCNCs have increased significantly with increase in MWNT concentration. FT-IR spectra and NMR spectra indicate the presence of both CH-π and π-π interaction between P3HT and MWNT. Thus, the increased conductivity and mechanical properties of P3HT in the easily processable MWNT-P3HT nanocomposite are interesting for its probable use in different optoelectronic appliances.