Thermoreversible gelation of helical polypeptide/single-walled carbon nanotubes and their solid-state structures.

Single-walled carbon nanotubes (SWCNTs) have been functionalized with poly(γ-benzyl- L-glutamate)s (PBLGs) having well-defined polymer molecular weight ( M_n = 7.5-21.1 kg·mol⁻¹) and molecular weight distribution (PDI = 1.05-1.20) by a graft-to method. Toluene solutions containing 5 wt % free PBLG and variable amounts of PBLG-functionalized SWCNTs (PBLG-SWCNTs) form gels at room temperature. Differential scanning calorimetry (DSC) analysis reveals that the gelation occurs thermoreversibly, in accord with previous studies on the pristine PBLG/toluene gels. The heat of gel melting (Δ H_m) is slightly elevated for the composite gels compared with the pristine gel, which suggests enhanced interactions between PBLGs in the former. But the gelation temperatures of the composites are unaffected by the presence of PBLG-SWCNTs. Small-angle X-ray scattering (SAXS) analysis of the composite and pristine gels at different temperatures by the Guinier method suggests that PBLG-SWCNTs promote interactions between PBLG rods, as indicated by the larger PBLG bundle size with increasing PBLG-SWCNT content in the gel and the melt state. W/SAXS analysis of the dry gels reveals that PBLG-SWCNTs induce significant changes in the PBLG packing order, resulting in a nematic phase, in contrast to a weakly ordered smectic C phase containing tilted PBLG rods that is observed in the pristine gel. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 [ABSTRACT FROM AUTHOR]