Mechanical agitation induces counterintuitive aggregation of pre-dispersed carbon nanotubes

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• 作者：Ricardo M.F. Fernandes^a ; ^b ; Matat Buzaglo^c ; Oren Regev^c ; ^d ; Istvá ; n Furó ; ^b ; Eduardo F. Marques^a ; ^{efmarque@fc.up.pt}
• 关键词：Single-walled carbon nanotubes ; Dispersion ; Surfactant ; Vortex-shaking ; Aggregation ; Network
• 刊名：Journal of Colloid and Interface Science
• 出版年：2017
• 出版时间：1 May 2017
• 年：2017
• 卷：493
• 期：Complete
• 页码：398-404
• 全文大小：1698 K
• 卷排序：493

文摘

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 10–60 s, power density ∼0.002 W mL−1), re-aggregation counterintuitively occurs. The initial dispersions are produced using surfactants as dispersants and powerful tip sonication (∼1 W mL−1) followed by centrifugation. Detailed imaging by light and electron microscopies shows that the vortex-induced aggregates consist of loose networks (1–102 μm 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 (∼0.03 W mL−1), the flocs break down and re-dispersal occurs. Molecular insight for the mechanism behind this surprising phenomenon is put forth.