title: Mechanical agitation induces counterintuitive aggregation of pre-dispersed carbon nanotubes.
abstract: Mechanical agitation is commonly used to fragment and disperse insoluble materials in liquids. However, here we show that when pristine single-walled carbon nanotubes pre-dispersed in water are subject to vortex-shaking for very short periods (typically 10-60s, power density ∼0.002WmL-1), re-aggregation counterintuitively occurs. The initial dispersions are produced using surfactants as dispersants and powerful tip sonication (∼1WmL-1) followed by centrifugation. Detailed imaging by light and electron microscopies shows that the vortex-induced aggregates consist of loose networks (1-102μm in size) of intertwined tubes and thin bundles. The average aggregate size increases with vortexing time in an apparently logarithmic manner and depends on the dispersant used, initial concentration of nanotubes and size distribution of bundles. The aggregation is, nonetheless, reversible: if the vortex-shaken dispersions are mildly bath-sonicated (∼0.03WmL-1), the flocs break down and re-dispersal occurs. Molecular insight for the mechanism behind this surprising phenomenon is put forth.
authors.affiliation: Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, P-4169-007 Porto, Portugal; Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
authors.forename: Ricardo M F
authors.initials: RMF
authors.lastname: Fernandes
authors.affiliation: Department of Chemical Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel.
authors.forename: Matat
authors.initials: M
authors.lastname: Buzaglo
authors.affiliation: Department of Chemical Engineering, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel; Ilse Katz Institute for Nanoscale Science and Technology, Ben-Gurion University of the Negev, 84105 Beer-Sheva, Israel.
authors.forename: Oren
authors.initials: O
authors.lastname: Regev
authors.affiliation: Division of Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology, SE-10044 Stockholm, Sweden.
authors.forename: István
authors.initials: I
authors.lastname: Furó
authors.affiliation: Centro de Investigação em Química, Department of Chemistry and Biochemistry, Faculty of Science, University of Porto, Rua do Campo Alegre, s/n, P-4169-007 Porto, Portugal. Electronic address: efmarque@fc.up.pt.
authors.forename: Eduardo F
authors.initials: EF
authors.lastname: Marques
keywords: Aggregation; Dispersion; Network; Single-walled carbon nanotubes; Surfactant; Vortex-shaking