Combined effect of cetyltrimethylammonium bromide and laponite platelets on colloidal stability of carbon nanotubes in aqueous suspensions

Abstract

The combined effect of cationic surfactant (cetyltrimethylammonium bromide, CTAB) and laponite platelets (laponite RD) on the stability of aqueous suspension of carbon nanotubes (NTs) has been investigated. The experimental methods include measurements of electrokinetic potential, radius of particles and aggregation stability. In individual suspensions the concentration of NTs was Cn=0.003% and concentration of laponite was Cl=0.5% and 2%. In hybrid NT+laponite suspensions the concentration of NTs was Cn=0.003% and 0.01% and the laponite/NT mass ratio, X=ml/mn, was varied within the range of X=0–1. For individual NTs and laponite species the increase of the CTAB concentration, Cs, changed the electrokinetic potential from negative to positive. However, the different effects of CTAB on stability of this species were observed: addition of CTAB stabilized the individual NTs and enhanced aggregation of laponite. The CTAB-induced overcharging was also typical for hybrid NT+laponite suspensions. Surprisingly, the minimum of a position of an isoelectric point Cs(IEP) (≈3·10−6M) at X≈0.1–0.3 was observed. This behavior can reflect the impact of CTAB on adhesion interactions between NTs and laponite platelets and adsorption of CTAB on individual NT and laponite species and their hybrids.