This work developed a novel approach for carbon nanotube (CNT) direct deposition on carbon fiber (CF) tow surface by chemical vapor deposition (CVD), without degrading CF mechanical properties. This approach combines conditions for growth at low-temperature (650°C), small growth induction period for a fast growth and fast surface modification to enable the growth. The lower growth temperature comes from using the well-known equimolar C₂H₂/CO₂ gas mixture. The floating catalyst from a liquid precursor (with high ferrocene concentration dissolved in hexane) reduced the growth induction period. Gentle surface modification, either by a mild oxidation of CF fiber with silicon containing sizing, or by desized CF exposition to a hexamethyldissiloxane (HMDSO) environment, create silicon oxide clusters. The X-ray Photoelectron Spectroscopy (XPS) analysis show that such clusters need to be in a higher oxidation state – Si(-O)₂, Si(-O)₃ and Si(-O)₄ – to anchor catalyst and enable CNT growth. The first oxidation state – Si(-O)₁ – is not enough. A resin droplet wetting test developed shows that even though the success in CNT growth, the entire processes decrease CF wetting, exposing the need for a resizing procedure. CF mechanical properties were characterized by single-filament and CF tow tensile strength tests.

This work developed a novel approach for carbon nanotube (CNT) direct deposition on carbon fiber (CF) tow surface by chemical vapor deposition (CVD), without degrading CF mechanical properties. This approach combines conditions for growth at low-temperature (650°C), small growth induction period for a fast growth and fast surface modification to enable the growth. The lower growth temperature comes from using the well-known equimolar C₂H₂/CO₂ gas mixture. The floating catalyst from a liquid precursor (with high ferrocene concentration dissolved in hexane) reduced the growth induction period. Gentle surface modification, either by a mild oxidation of CF fiber with silicon containing sizing, or by desized CF exposition to a hexamethyldissiloxane (HMDSO) environment, create silicon oxide clusters. The X-ray Photoelectron Spectroscopy (XPS) analysis show that such clusters need to be in a higher oxidation state – Si(-O)₂, Si(-O)₃ and Si(-O)₄ – to anchor catalyst and enable CNT growth. The first oxidation state – Si(-O)₁ – is not enough. A resin droplet wetting test developed shows that even though the success in CNT growth, the entire processes decrease CF wetting, exposing the need for a resizing procedure. CF mechanical properties were characterized by single-filament and CF tow tensile strength tests.