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

Abstract

The crystal morphology of poly­(ε-caprolactone)/multiwalled carbon nanotube (PCL/MWCNT) blends and MWCNT-g-PCL grafting polymers crystallized in n-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 b-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.

The formation of a nanohybrid shish-kebab (NHSK) structure in melt-processed composites of poly(ethylene terephthalate) (PET) and multi-walled carbon nanotubes (MWCNTs)

“…The crystallization kinetics revealed a confined crystallization process giving rod or disc-like crystallites. Similar results have been reported by Zhou [28], for PCL-MWCNT solution crystallized composites, where the initial helical wrapping of polymer chains act as nucleation points for crystallites to grow with random orientationsthis can then straighten the MWCNT (depending on MWCNT diameter and length).…”

Specific Disassembly of Lamellar Crystalline Micelles of Block Copolymer into Cylinders

“…Herein we propose that the disassembly of PCL 67 - b - PDM 41 lamellar crystalline micelles proceeds via a micelle core/additive interaction mechanism, i.e., through the moderate H-bonding interaction between PCL crystals inside the micelles and n -hexanol. Since n -hexanol is frequently used as the solvent for growth of PCL single crystals, the following two factors can be inferred from this: (1) n -Hexanol can partially dissolve PCL, especially low molecular weight PCL (for example, the PCL block in PCL 67 - b - PDM 41 ). (2) The PCL crystals will not be completely destroyed by n -hexanol at low temperature, which can be confirmed by WAXS, DSC, and FTIR results (Figures and ).…”

“…However, such an interaction should not be too strong so that the crystallinity of the micellar core would not be completely destroyed. Since n -hexanol is usually used to culture single crystals of PCL, it can dissolve PCL at high temperature, but PCL can also crystallize from n -hexanol solution at low temperature. As a result, we speculate that there exists a weak interaction between n -hexanol and PCL in the micellar core, and n -hexanol was chosen as the additive.…”

Spatially Restricted Templated Growth of Poly(ε-caprolactone) from Carbon Nanotubes by Crystallization-Driven Self-Assembly

“…The biocompatible and biodegradable properties of the hierarchical structure are important because of the potential application in biorelated fields. Generally, it is hypothesized that the existence of CNTs will exert a nucleation effect on polymer crystallization, leading to a core–shell structure or so-called “shish-kebab” nanocomposites . For example, Winnik reported a hierarchical structure by growing PFS homopolymer crystals onto multiwalled CNTs to form a “shish-kebab” structure, and the subsequent addition of PFS-based BCPs resulted in hairy caterpillar structures .…”