BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 40

possess high strength and gel-spinning results in high draw ratio and consequently
high orientation and modulus.
1.1.6.7.5 ELECTROSPINNING OF CNT/POLYMER FIBERS
Electrospinning is an electrostatic induced self-assembly process, which has been
developed for decades, and a variety of polymeric materials have been electro
spun into ultra-fine filaments [22]. Electro spinning of CNT/polymer fibrils is
motivated by the idea to align the CNTs in a polymer matrix and produce CNT/
polymer nanocomposites in a continuous manner. The alignment of CNTs en-
hances the axial mechanical and physical properties of the filaments. Recently
researchers have adopted the coelectro spinning technique for processing CNT/
PAN (polyacrylonitrile) and GNP (graphite nanoplatelet)/PAN fibrils. The fluid is
contained in a lass syringe, which has a capillary tip (spinneret). When the volt-
age reaches a critical value, the electric field overcomes the surface tension of the
suspended polymer and a jet of ultra-fine fibers is produced. As the solvent evapo-
rates, a mesh of nano to micro size fibers is accumulated on the collection screen.
The fiber diameter and mesh thickness can be controlled through the variation
of the electric field strength, polymer solution concentration and the duration of
electro spinning. In the processing of CNT/PAN nanocomposite fibrils, polyac-
rylonitrile with purified high-pressure CO disproportionation (HiPCO) SWCNTs
dispersed in dimethyl formamide, which is an efficient solvent for SWCNTs, are
coelectron spun into fibrils and yarns. CNT-modified surfaces of advanced fibers
prepared first time as modified the surface of pitch-based carbon fiber by grow-
ing carbon nanotubes directly on carbon fibers using chemical vapor deposition.
When embedded in a polymer matrix, the change in length scale of carbon nano-
tubes relative to carbon fibers results in a multiscale composite, where individual
carbon fibers are surrounded by a sheath of nanocomposite reinforcement. Single-
fiber composites have been fabricated to examine the influence of local nanotube
reinforcement on load transfer at the fiber/matrix interface. Results of the single-
fiber composite tests indicate that the nanocomposite reinforcement improves in-
terfacial load transfer. Selective reinforcement by nanotubes at the fiber/matrix
interface likely results in local stiffening of the polymer matrix near the fiber/
matrix interface, thus, improving load transfer. The interfacial shear strength of
CNT coated carbon fibers in epoxy was studied using the single-fiber composite
fragmentation test. Randomly oriented MWCNTs and aligned MWCNTs coated
fibers demonstrated a 71% and 11% increase in interfacial shear strength over
unsized fibers. Researchers attributed this increase to the increase in both the
adhesion of the matrix to the fiber and the interphase shear yield strength due to
the presence of the nanotubes. Another method to exploit the axial properties of
CNTs is to assemble them into a macroscopic fiber, with the tubes aligned parallel
with the fiber axis; a strategy similar to that proposed eight decades ago for the
development of high-performance polymer fibers. Carbon nanotube fibers can be
produced by drawing from an array of vertically aligned CNTs, by wet-spinning