Carbon black dispersions in surfactant-based microemulsion
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Dominique Guyomard and Bernard Lestriez Institut des Matériaux Jean Rouxel, Centre National de la Recherche Scientifique (CNRS), Université de Nantes, Nantes Cedex 3 44322, France (Received 1 October 2017; accepted 16 November 2017)
In an attempt to introduce a novel approach to formulate carbon black (ketjen black) suspension with enhanced colloidal stability, improved flowability, and higher conductivity, ketjen black was dispersed in microemulsion systems composed of a non-ionic surfactant (Triton X100), decanol, and water. Rheo-electric and rheo-microscopy proved to be very powerful techniques that are able to elucidate the microstructure evolution with the composition and under shear flow. Interestingly, the carbon black slurries at low decanol/water ratio are weak gels (flowable) with higher electrical conductivity than those at higher ratio, which shows strong-gel viscoelastic response. In addition, the slurries show recoverable electrical behavior under shear flow in tandem with the viscosity trend. It is likely that the oil-in-water microemulsion enhances slurries’ stability without affecting the percolating network of carbon black. On the other hand, the oil-in-water analogous and bilayer structure of the lamellar phase makes the slurries less conductive as a consequence of losing the network percolation.
I. INTRODUCTION
To enhance the energy and power densities of electrodes for energy storage systems, the formulation and processing of electrode slurries proved to be a critical issue in determining the electrode performance. Carbonaceous materials such as carbon black (CB), nanotubes, and nanofibers are main conductive additives in the electrode slurries.1,2 These materials are characterized by exceptional chemical stability and electrical and mechanical properties derived from their large diversity of structure that extends from the sp2-hybridization of carbon atoms to the crystalline structure (degree of graphitization). Among various kinds of carbonaceous materials, semispherical (three-dimensional) CB has a unique place in the formulations of electrodes for energy storage systems.3,4 CB is initially formed from semispherical primary particles of nanometric (few hundred nm) size, which are fused to form aggregates (few lm size scale) in suspensions. The van der Waals attraction forces drive the aggregates to bind into larger loosely agglomerates (10–100 lm).5 The surface area and surface chemistry of CB play a pivotal role in determining the strength of binding forces6 which determines the microstructure and hence the flow behavior of CB suspensions.7 Above a critical concentration, the so-called percolation Contributing Editor: Yat Li a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.451
threshold, a three-dimensional network is formed across the CB suspension showing abrupt increase of the rheological parameters (viscosity, shear modulus, and yield stress) and electrical conductivity of the suspension.5,8 This behavior is a consequence of formation of the pe
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