Flow-Induced Microstructure in Aqueous Cationic Surfactant Solution in the Presence of Structure-Enhancing Additives

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In the present article, we report the flow-induced microstructure in a dilute wormlike micellar solution of cetyltrimethylammonium bromide (CTAB). The additive used here is sodium salicylate (NaSal) to enhance the supramolecular structure formation. The flow-induced microstructures in surfactant solution were reproduced by the in situ gelation of the substrate. A silicon alkoxide of tetramethylorthosilicate (TMOS) in aqueous hydrochloric acid was used as a silica precursor to capture the microstructure. The captured flow-induced structures in the wormlike micellar solution show alignment to the direction of flow under a weak flow. Meanwhile, at high shear rates, flow-induced coagulation or layer fluctuations occur. The flow-induced morphologies are dependent on the surfactant concentration, molar ratio of NaSal to CTAB, and flow intensity. SEM images taken from the direct observations through in situ gelation are consistent with the rheological responses such as shear thinning or shear thickening behavior.
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