Rheology of wormlike micellar gels formed by long-chained zwitterionic surfactants

Abstract

Long-chained surfactant solutions have found widespread use in the oil and gas industry due to a host of attractive properties. In this paper, we characterize one such commercially used viscoelastic surfactant that forms a wormlike micellar gel at room temperature and a viscoelastic solution at higher temperatures. We probe both states by conducting linear and nonlinear rheological tests and analyze their behavior under the framework of micellar rheology. Our study outlines departure from behavior exhibited by more conventional micellar systems and uncovers interesting dynamics like shear-induced fracture and possible shear-banding in these materials. In doing so, we provide a detailed understanding of a novel class of wormlike micellar solutions.

Shear layers and plugs in the capillary flow of wormlike micellar gels

“…4 must be interpreted as a sign of possible transient shearbanding. In the absence of better resolved measurements, we cannot comment on if these bands persist in steady-state, but as mentioned in our previous work, 46 its likely that entanglement kinetics 31 leads to shear-banding in our wormlike micellar gel system at some level, possibly in a mechanism akin to that proposed for soft glassy matter. 50,89 The stress plateau is followed by the high-shear rate branch that, for conventional surfactant solutions, is usually only accessible via capillary rheometry.…”

“…3 we see that for more than two decades in frequency o, the storage modulus G 0 is independent of o, whereas the loss modulus G 00 is independent of o in the low o regime while having a power-law like dependence for higher o, reminiscent of the anomalous increase in G 0084 with o reported for Carbopol. [85][86][87] The lack of a crossover in G 0 and G 00 in the range of o probed indicates very long structural relaxation times 40,41,46 and the fact that values of G 0 are larger than G 00 by almost an order of magnitude (atleast for 2,3% solutions) motivates us to refer to these VES solutions as wormlike micellar gels. Note, that these wormlike micellar gels exhibit a sort of gel-sol transition with temperature, where at higher temperatures, their linear rheology is that of a Maxwell-type viscoelastic fluid with a single relaxation time.…”

“…45 For this paper, our system under investigation is a WLM gel formed by these types long-chained surfactants. 41,46 While there have been studies on the self-assembly and rheology of WLM gels in the last two decades, few studies have focussed on the flow dynamics of these complex materials. Previous studies from our group have documented the general gel-formation tendencies of long-chained surfactants and their turbulent drag reduction features.…”

“…47,48 More recently, it was shown that WLM gels show evidence of interesting features like long-lived transient shear-banding and shear-induced fracture. 46 More generally, the highly elastic nature of WLM gels leads to differences in behaviour when compared to the flow of more conventional WLM solutions. 49,50 Thus, WLM gels must be treated as a model system whose rheology and behaviour in different flows deserves further investigation.…”

“…49,50 Thus, WLM gels must be treated as a model system whose rheology and behaviour in different flows deserves further investigation. 51 Having systematically studied the linear and non-linear rheology (using a rheometer) of wormlike micellar gels formed by long-chained zwitterionic surfactants in an earlier paper, 46 here we focus on the behaviour of these gels when they flow in narrow, round capillaries.…”