pH‐reversible destabilization‐dispersion of MWCNTs coated with functional plasma polymer films in water

The stability in water of multi‐walled carbon nanotubes (MWCNTs) coated with N‐ or O‐rich plasma polymers (PPs) is investigated at dif­ferent pH values. MWCNTs are coated with PPs by plasma enhanced chemical vapor deposition of ethylene and ammonia or ethylene and car­bon dioxide. MWCNTs coated with N‐rich PP in water at pH 12 exist as agglomerates that readily sediment, whereas, the agglomerate size de­creases and suspension stability increases as the pH changes from 10 to 2. The reverse effect is observed for MWCNTs coated with O‐rich PP which form agglomerates at pH 2, but are stable from pH 4–12. By switching the pH of suspensions containing either one of these coated MWCNTs, it is possible to cycle through destabilization and dispersion steps. MWCNTs coated with N‐ or O‐rich plasma polymers in water can be destabilized and redispersed through pH cycling. Charged nitrogen groups at pH 2 allow MWCNTs to remain stable in suspension, whereas agglomeration and sedimentation is observed at pH 12. The reverse trend is observed for the oxygen‐containing coating deposited on MWCNTs.