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Elastic instability and elastic wave phenomena can be seen for the flow of a wormlike micellar solution past a confined microfluidic cylinder once the Weissenberg number exceeds a critical value.

This study presents an extensive numerical investigation on the flow characteristics of wormlike micellar (WLM) solutions past a single and vertically aligned two microcylinders placed in a microchannel in the creeping flow regime. The rheological behavior of the micellar solution is realized based on the two-species Vasquez–Cook–McKinley (VCM) constitutive model, which takes into account both the breakage and re-formation dynamics of micelles. For the case of single microcylinder, as the blockage ratio (ratio of the cylinder diameter to that of the channel height) is gradually varied, we find the existence of a flow bifurcation in the system, and also a gradual transition for a range of flow states, for instance, steady and symmetric or Newtonian like, steady and asymmetric, unsteady periodic and asymmetric, unsteady quasi-periodic and asymmetric, and, finally, unsteady quasi-periodic and symmetric. For the case of two microcylinders, we observe the presence of three distinct flow states in the system, namely diverging (D), asymmetric-diverging (AD), and converging (C) states as the intercylinder spacing in between the two cylinders is varied. Similar types of flow states are also observed in the recent experiments dealing with WLM solutions. However, we show that either this transition from one flow state to another in the case of a single microcylinder or the occurrence of any flow state in the case of two microcylinders is strongly dependent upon the values of the Weissenberg number and the nonlinear VCM model parameter ξ, which basically indicates how easy or hard it is to break a micelle. Based on the results and discussion presented herein for the single and two microcylinders, we hope this study will facilitate the understanding behind the formation of preferential paths or lanes during the flow of viscoelastic fluids through a porous media, which was seen in many prior experiments in the creeping flow regime.

In this study, the rheological behavior of polyacrylamide solutions in the absence and presence of cationic Gemini surfactants (16-s-16, s = 5, 6) and their monomeric counterpart, cetyltrimethylammonium bromide, at different temperatures has been studied in the light of its application field by rheometry. The polyacrylamide solution shows the shear thinning behavior at a very low shear rate in the absence and presence of surfactants, and the Ostwald de model was used to describe the pseudoplastic behavior of polyacrylamide solution. The viscosity of polyacrylamide solution increases with the addition of surfactants, and the increase in viscosity is quite significant with Gemini surfactant as compared with their monomeric counterpart cetyltrimethylammonium bromide, indicating stronger interaction of polyacrylamide with Geminis. Further, transmission electron microscope results support the viscosity data. The results obtained are quite interesting and could be of prolific use for selection of polymer-surfactant mixtures and surfactants for use in enhance oil recovery.