BASIC CONCEPTS AND AN OVERVIEW - Foundations of Nanotechnology: Pore Size in Carbon-Based Nano-Adsorbents - page 34

FIGURE 1.3 Schematic model of CNTs-grafted carbon fiber filament.

An effective strategy for positioning, integration and interrogation of a single
nanofiber requires controlled electro spinning as detailed elsewhere. Researchers
also determine the maximum concentration of CNTs in PAN that allows good
electro spin ability of the precursor polymer to carbon nanowires. Overall fabrica-
tion methodology is a combination of three techniques: (1) photolithography to
produce an MEMS structure, (2) self-assembled electro spinning of functional-
ized CNTs in PAN solution to form nanowires anchored on the MEMS platform,
and (3) controlled pyrolysis to obtain carbon composite wires integrated with the
underlying carbon MEMS structure. Four different concentrations of CNTs in
PAN for electro spinning were prepared by mixing 0.05, 0.1, 0.2 and 0.5 wt.%
CNTs in 8 wt.% PAN in DMF. The detailed method for solution preparation is
described elsewhere. These solutions were electrospun using Dispovan syringe
(volume: 2.5 mL and diameter: 0.55 mm) at 13-15 kV on the MEMS structures
fabricated earlier. The distance between the tip of the jet and the MEMS collector
was 10 cm, and the flow rate of the solution was maintained at 1 L/min Electro
spinning was performed for a short period of 5-10 s to limit the number of wires
and to obtain single wires suspended between posts. The resulting structures con-
sisting of suspended composite nanowires on polymers were stabilized in air at
250°C for 1 h prior to pyrolizing the whole structure which is done under N 2 low
(flow rate: 0.2 L/min) at 900°C for 1 h, with a ramp time of 5°C/min, to yield a
monolithic carbon structure having good interfacial contacts and with electrically
conducting posts of much greater cross-sectional area than the nanofibers them-
selves.
Carbon fibers used in this study are (i) a low thermal conductivity and ultra-
high tensile strength PAN-based (T1000GB) carbon fiber and (ii) a high thermal
conductivity and ultrahigh modulus pitch-based (K13D) carbon fiber. Note that as
received, both fibers had been subjected to commercial surface treatments and sizing