Surface functionalization of quartz fibres via direct carbon nanotube growth. A comparison between thermal and plasma-enhanced CVD

This work investigates the surface functionalization of quartz fibres via direct carbon nanotube (CNT) synthesis as a route to tailored multiscale and multifunctional interfaces in advanced composite systems. Thermal and plasma-enhanced chemical vapour deposition (PE-CVD) are systematically compared to elucidate the relationship between synthesis conditions, CNT morphology, fibre mechanical integrity, and surface physico-chemical and functional properties. While conventional thermal CVD at 620–640 °C induces a severe degradation of the original fibre tensile strength (≈74%), PE-CVD enables the growth of a dense layer of radially aligned CNTs at lower temperatures (520–540 °C), thereby mitigating the thermal contribution to fibre strength degradation, although additional strength loss still occurs during catalyst-assisted CNT synthesis. Microscopic (SEM, TEM, AFM) and spectroscopic (Raman, EDS, EELS) analyses demonstrate that plasma assistance promotes CNT growth despite incomplete catalyst nanoparticle formation at low annealing temperatures, yielding CNTs with smaller diameters (≈12 nm), hollow cores, and reduced tortuosity. Wettability, surface-energy and single fibre fragmentation analyses demonstrate that CNT decoration enhances fibre–epoxy interfacial adhesion, resulting in an approximately 31% increase in interfacial shear strength through improved physico-chemical affinity and mechanical interlocking. Finally, CNT-modified quartz fibres demonstrate electrochemical activity for hydrogen peroxide generation, highlighting their potential as reinforcements in multifunctional composite materials for environmental remediation applications.