Paper MS+PS+TF-ThA4
Multifunctional Fabrics via Tungsten ALD on Kevlar

Thursday, November 13, 2014, 3:20 pm, Room 302

Multifunctional materials combine two or more distinct capabilities into a single article unit. Kevlar is a high strength fiber used for personal protection and other mechanically demanding applications. Adding conductivity to Kevlar creates a new multifunctional protective/electronic material for electromagnetic shielding, communications, and erosion resistant, anti-static fabrics and cables for space and automotive technologies. For this study, we coated Kevlar fibers and woven mats with ALD tungsten, using WF₆ and dilute silane (SiH₄, 2% Ar) at 220°C. Kevlar’s thermal stability makes it a very amenable polymer for ALD coating at relatively high temperatures. Before W ALD, we deposited a TiO₂/Al₂O₃ bilayer by ALD onto the Kevlar, at various temperatures (50- 220°C). The Al₂O₃ layer promotes W nucleation. The TiO₂ layer is important because previous mechanical analysis indicates that the TMA precursor degrades the Kevlar polymer backbone, whereas TiO₂ ALD using TiCl₄ and H₂O was less damaging. XPS analysis confirms the presence of TiO₂, Al₂O₃ and W on the fibers after each coating step. After W ALD, the yarns and mats are highly conductive (~3000 S/cm) and remain flexible. Tensile testing shows that upon coating with 20 ALD cycles, the strength of the Kevlar decreases from 3.32 GPa to 3.02 GPa. The ability to create highly conductive Kevlar with mechanical strength within 90% of the original mechanical performance could open new areas of application for large area low temperature ALD processing.