title: Surface properties of CNTs and their interaction with silica.
abstract: In order to improve the embedding of carbon nanotubes (CNTs) in cement-based matrices, silica was deposited on the sidewall of CNTs by a sol-gel method. Knowledge of the conditions of CNTs' surfaces is a key issue in understanding the corresponding interaction mechanisms. In this study various types of CNTs synthesized using acetonitrile, cyclohexane, and methane were investigated with regard to their physicochemical surface properties. Significant differences in surface polarity as well as in the wetting properties of the CNTs, depending on the precursors used, were revealed by combining electro-kinetic potential and contact angle measurements. The hydrophobicity of CNTs decreases by utilising the carbon sources in the following order: cyclohexane, methane, and finally acetonitrile. The XPS analysis, applied to estimate the chemical composition at the CNT surface, showed nitrogen atoms incorporated into the tube structure by using acetonitrile as a carbon source. It was found that the simultaneous presence of nitrogen- and/or oxygen-containing sites with different acid-base properties increased the surface polarity of the CNTs, imparting amphoteric characteristics to them and improving their wetting behaviour. Regarding the silica deposition, strong differences in adsorption capacity of the CNTs were observed. The mechanism of silica adsorption through interfacial bond formation was discussed.
authors.affiliation: Institute of Construction Materials, Faculty of Civil Engineering, Technische Universität Dresden, D-01062 Dresden, Germany.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Sobolkina
authors.forename: Viktor
authors.initials: V
authors.lastname: Mechtcherine
authors.forename: Cornelia
authors.initials: C
authors.lastname: Bellmann
authors.forename: Vyacheslav
authors.initials: V
authors.lastname: Khavrus
authors.forename: Steffen
authors.initials: S
authors.lastname: Oswald
authors.forename: Silke
authors.initials: S
authors.lastname: Hampel
authors.forename: Albrecht
authors.initials: A
authors.lastname: Leonhardt
keywords: Adsorption mechanism; Carbon nanotubes; Cement-based composites; Electro-kinetic potential; Silica adsorption; Wetting behaviour