Colloids and Surfaces A: Physicochem. Eng. Aspects 404 (2012) 25–35 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects jo ur nal homep a ge: www.elsevier.com/locate/colsurfa Investigating the effectiveness of PEO/PPO based copolymers as dispersing agents for graphitic carbon black aqueous dispersions S. Yasin, P.F. Luckham ∗ Department of Chemical Engineering & Technology, Imperial College, South Kensington, Post Code: SW7 2AZ, London, United Kingdom a r t i c l e i n f o Article history: Received 6 October 2011 Received in revised form 4 April 2012 Accepted 6 April 2012 Available online 12 April 2012 Keywords: Graphitic carbon dispersions Rheology Surfactant adsorption Conductivity AFM a b s t r a c t The dispersability of graphitic carbon black, selected as a model for carbon nanotubes, has been investi- gated using a combination of rheological, conductivity and atomic force microscopy (AFM) techniques. The effectiveness of three PEO/PPO based non-ionic dispersants, namely polyethylene oxide polypropy- lene oxide ABA copolymers (synperonic PE/F 103 with 2 × 16 ethylene oxide units and PE/F 108 with 2 × 148 ethylene oxide units) and NPE1800 (nonyl phenyl polypropylene oxide-polyethylene oxide with 27 ethylene oxide units), is reported. Adsorption isotherms were determined for these dispersants. The adsorption isotherms of PE/F 103 in comparison with PE/F 108 revealed that in molar terms (mol/m 2 ) the adsorption decreases for PE/F 108 with more ethylene oxide units, indicating that adsorption is governed by size of the PEO (polyethylene oxide) chain length. Also, the synperonic PE series which has polypropylene oxide as an anchor group and does not contain any aromatic ring in their anchoring group, gave lower adsorption amounts (in moles) as compared to the NPE 1800 which contains an aromatic ring (nonyl phenyl) in its anchoring group as well as propyleneoxide. The relative viscosity-effective volume fraction ˚ ′ curves are compared with the theoretical curves for the hard sphere dispersions calculated using Krieger–Dougherty equation. For the graphitic carbon black studied here, in an aqueous medium, neither PE/F 103, nor PE/F 108 showed good agreement with the Krieger–Dougherty equation; the vis- cosities were all much higher than that predicted by that equation. Whilst NPE 1800 produced dispersions of lower viscosity and the viscosity values showed a good agreement with the Krieger–Dougherty equa- tion. The results achieved from oscillatory measurements showed that PE/F 103 and PE/F 108 dispersants showed a frequency cross-over of G ′ and G ′′ at lower volume fractions. Also they produced dispersions of high electrical conductivity, suggesting that these systems are aggregated. In the AFM force spectroscopy measurements, the interactions between the adsorbed layers of PE/F103 were initially attractive, whilst somewhat surprisingly the PE/F 108 adsorbed layers only showed repulsive interactions on approach and separation. NPE 1800 stabilised systems exhibited much lower viscosity and elastic modulus than the PE/F stabilised dispersions; produced dispersions of lower electrical conductivity and showed repul- sive interactions in AFM, suggesting that these systems are much more stable than the carbon black dispersions bearing adsorbed PE/F polymers. The results indicated that synperonics (PE/F 103 and PE/F 108) are not a good dispersants for graphitic carbon black and by consequence for carbon nanotubes; whilst NPE 1800 is a suitable dispersant for these dispersions and could be a good dispersant for carbon nanotubes. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Carbon nanotubes are nanometre scale wires with the potential of benefiting mankind in many ways because of their extraordinary mechanical, electrical, optical and thermal properties [1–4]. Car- bon nanotubes pack themselves into ropes which further aggregate and this aggregation is an obstacle to many applications [5]. This ∗ Corresponding author. Tel.: +44 0 2075945583; fax: +44 0 2075945636. E-mail addresses: s.yasin@imperial.ac.uk (S. Yasin), p.luckham01@imperial.ac.uk (P.F. Luckham). problem has motivated considerable recent research to develop methods to disperse the nanotubes more effectively [6]. The use of ultrasound has achieved some success in dispersing carbon nanotubes, but this method tends to damage the inter- nal structure of the tubes [7]. Physical adsorption of polymeric layers that will act as a steric stabilizer is an alternative [8,9]. Graphitic carbon black possesses largely a uniform surface, like carbon nanotubes, composed of aromatic carbon rings owing to crystalline nature of the two materials. Graphitic carbon is chemi- cally inert and stable, hence does not react with the environment. Also graphitic carbon black particles in a solution/suspension, like carbon nanotubes have a tendency to pack themselves and settle 0927-7757/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfa.2012.04.001