Experimental Study of Pressure Loss and Rheo-Optical Behavior of CTAB/NaSal Aqueous Solution under Elongational Flow

Abstract

In a previous paper we clarified the behavior of pressure losses DP for aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal) in an elongation dominant flow through slots: the flow curves relating DP to the apparent elongational rate consisted of three characteristic regions. In particular, DP increased largely in a specific region II, and this characteristic was suggested to be closely connected to the flow induced structure (FIS). However, it could not be asserted that FIS solely causes the large increase in DP, because vortices were also found in the flow upstream of the slot in region II and such vortices are known to induce large pressure drops frequently. In the present experiment, we used a nozzle providing almost the same constant elongational rate as the slot in order to eliminate the influence of vortices on DP, estimated elongational rates of the upstream flow, compared DP for both the slot and the nozzle, and concluded that vortices existing in the region upstream of the slot do not give a significant effect on DP. Next, the image of small angle light scattering (SALS) was examined to clarify the developing process of FIS: A butterfly-type and streak-type combined pattern in SALS occurs in region II, indicating the generation of FIS; the streak-type pattern degenerate at higher elongational rates in region III, meaning a partial collapse of FIS generated in region II; change in FIS depends not only on strain rate but also on strain in elongational flow. Moreover it was found that FIS shows a step-like development in the upstream flow of constant elongational rate.

Flow Properties of Several Types of Liquid Flows through Micro-Orifices

“…Also, 2∆p/ρV 2 for AE (nonionic surfactant) rose up steeply at a particular Re. Okawara et al have shown structure of surfactant micelle was changed by passing though small apertures (23) . The steep rises for AE solution were caused by structure changes.…”

Elongational deformation of wormlike micellar solutions

“…Early investigations were based on opposed jet experiments ; Lu et al (1998);Prud'homme and Warr (1994); Walker et al (1996); Chen and Warr (1997)], four-roll mill experiments [Kato et al (2002); Kato et al (2004); Kato et al (2006)], entrance flow [Okawara et al (2008); Okawara et al (2009)], two-dimensional squeeze flow [Takahashi and Sakata (2001)], and flow through porous media experiments [Muller et al (2004)] showing an elongational hardening (increase of elongational viscosity with increasing elongation rate) of WLM solutions which is attributed to strong alignment of the micelles in flow direction. However, all these experiments were not purely extensional or had an unknown preshear history.…”

“…However, it could not be resolved whether the increase in R G observed at low elongation rates is just due to alignment and elongation of micelles in flow direction or whether fusion of micelles occurs increasing the average micellar contour length [Chen and Warr (1997)]. Okawara et al [Okawara et al (2008); Okawara et al (2009)] investigated the pressure loss Dp of CTAB/NaSal solutions (c s ¼ 30 mM) at high salt/surfactant ratios R flowing through two different converging channels and analyzed structural changes using simultaneous SALS experiments. For a distinct apparent elongation rate regime (regime II), a strong increase of Dp with increasing elongational rate has been observed.…”

Flow Properties of Microbubble/Polyethylene Glycol Mixtures Passing through Orifices and Slits

“…Okawara et al 7) measured the pressure drop in slit flows of a wormlike micelle surfactant and found that flow properties changed as the surfactant structure was changed. Ouchi et al 8) conducted an experiment using an aqueous solution of cetyltrimethylammonium bromide and sodium salicylate, which form wormlike micelles, and reported on the shear induced structure and instabilities.…”