Straightening Single-Walled Carbon Nanotubes by Adsorbed Rigid Poly(3-hexylthiophene) Chains via π–π Interaction

The straightened morphology of single-walled carbon nanotubes (SWCNTs) driven by rigid and conjugated regioregular poly­(3-hexyl­thiophene) (rr-P3HT) and the related mechanism were studied with transmission electron microscopy (TEM), atomic force microscopy (AFM), and spectroscopic methods. It was found that bent SWCNTs could be straightened significantly in solutions with low SWCNT concentration, which was quantitatively confirmed by the increased persistence length. UV–vis and photoluminescence spectroscopic studies revealed that there exists strong π–π interaction between P3HT chains and SWCNTs. The P3HT chains also became more rigid after interaction with SWCNTs. We proposed that SWCNTs were straightened by the coaxially adsorbed P3HT chains instead of epitaxial P3HT crystals. Multiwalled carbon nanotubes (MWCNTs) could not be straightened by P3HT under the same conditions, showing that the straightening force was limited. This result may be useful in preparation of aligned arrays of SWCNTs/conjugated polymer supramolecular structures

Straight and Rod-like Core–Sheath Crystals of Solution-Crystallized Poly(ε-caprolactone)/Multiwalled Carbon Nanotube Nanocomposites

The crystal morphology of poly­(ε-caprolactone)/multiwalled carbon nanotube (PCL/MWCNT) blends and MWCNT-<i>g</i>-PCL grafting polymers crystallized in <i>n</i>-hexanol was investigated. Two typical morphologies are observed: a straight and rod-like core–sheath structure with embedded MWCNTs as the core and PCL polycrystals of high crystallinity as the sheath, and a bent double-layer structure with MWCNTs covered by a PCL layer of low crystallinity. It is found that thinner (outer diameter <15 nm) and shorter (length <2 μm) MWCNTs are easier to be straightened by PCL crystals, and the grafted PCL chains have weaker crystallizability due to structural confinement and thus a weaker ability of straightening MWCNTs. Electron diffraction and high-resolution transmission electron microscopy reveal that the PCL crystals are randomly orientated with the <i>b</i>-axis perpendicular to the MWCNT surface. The growth direction of the PCL crystals is not perpendicular to the axis of MWCNT, possibly due to the nucleation effect of the preadsorbed PCL chains in the solution, which helically wrap MWCNTs. This leads to wrapping and straightening of MWCNTs by rigid PCL crystals

Hydrogen-Bonding-Mediated Fragmentation and Reversible Self-assembly of Crystalline Micelles of Block Copolymer

Two hydrogen (H)-bond donors, phenol and l-threonine, were added into the aqueous solutions containing crystalline micelles of a poly­(ε-caprolactone)-<i>b</i>-poly­(ethylene oxide) (PCL-<i>b</i>-PEO) block copolymer, respectively. Dynamic light scattering (DLS) characterization showed that the micellar size became smaller after addition of phenol. Transmission electron microscopy (TEM) results revealed that the long crystalline cylindrical micelles formed in the neat aqueous solution were fragmented into short cylinders and even quasi-spherical micelles, as the phenol concentration increased. By contrast, the spherical PCL-<i>b</i>-PEO crystalline micelles could be transformed into short cylinders and then long cylinders after addition of l-threonine. Reversible morphological transformation was realized for the PCL-<i>b</i>-PEO crystalline micelles by adding these two H-bond donors alternately. It is confirmed that both phenol and l-threonine could form H-bonds with PEO. We proposed that, the micellar corona was swollen by phenol, leading to fragmentation of the micellar core, whereas the PEO blocks in the micellar corona was dynamically cross-linked by l-threonine beacuse of its multiple H-bond-donation groups, resulting in a smaller reduced tethering density