Broad Bandwidth Optical and Mechanical Rheometry of Wormlike Micelle Solutions

Abstract

We characterize the linear viscoelastic shear properties of an aqueous wormlike micellar solution using diffusing wave spectroscopy (DWS) based tracer microrheology as well as various mechanical techniques such as rotational rheometry, oscillatory squeeze flow, and torsional resonance oscillation covering the frequency range from 10 ÿ1 to 10 6 rad=s. Since DWS as well as mechanical oscillatory squeeze flow and torsional resonance oscillation cover a sufficiently high frequency range, the persistence length of wormlike micelles could be determined directly from rheological measurements for the first time.PACS numbers: 83.80. Qr, 82.70.ÿy, 83.60.Bc, 83.85.Ei Significant progress has been made over the past decade in developing optical microrheology as a noninvasive means to study the rheological properties of soft complex fluids. Following the seminal Letter of Mason and Weitz in 1995 [1], several hundred studies have reported on the application of optical microrheology to such diverse systems as polymers, emulsions, gels, biomaterials, hydrogel scaffolds, stomach mucus, magnetic fluids, ceramics, slurries, and many more [1][2][3][4][5]. The underlying idea is to study the response of small (colloidal) particles embedded in the system under study. The motion of probe particles can either be controlled actively, e.g., using optical tweezers or one can analyze the thermal motion of particles to obtain information about the viscoelastic properties of the surrounding fluid. The latter can be achieved by using diffusing wave spectroscopy (DWS) [6]. DWS provides a fast ensemble average of the tracer motion and can resolve extremely fast displacements on the order of microseconds with subnanometer resolution. Despite the large literature, benchmarking optical microrheological techniques with macroscopic mechanical measurements is still not concluded. Almost all comparisons between microrheology and macrorheology have been restricted to the frequency range <10 2 rad=s due to mechanical limitations and inertial effects in the gap loading limit of conventional rotational rheometers and the limited availability of mechanical devices operating at higher frequencies [7][8][9].Here we apply both DWS and macroscopic mechanical rheometry to characterize an aqueous solution of cetylpyridinium chloride and sodium salicylate (100mM CPyCl-60mM NaSal) at different temperatures. These solutions display complex viscoelastic properties but are easy and reproducible to prepare and stable in time. They exhibit fast dynamics and the structural features are much smaller than the tracer particles. The latter is an important requirement for the successful application of tracer microrheology which might otherwise lead to erroneous results [4]. Because of the peculiar viscoelastic behavior such systems have found wide commercial application ranging from personal care to enhanced oil recovery products [10]. Rapid access to microscopic structural and dynamic properties is therefore of interest both from a fundamental and an applied point of vi...

Desmin and Vimentin Intermediate Filament Networks: Their Viscoelastic Properties Investigated by Mechanical Rheometry

“…The onset of this ω 3/4 scaling is related to the highest Zimm relaxation frequency ω 0 = k B T/8η s l p 3 , which can also be used to obtain the persistence length l p . This concept has been successfully used to determine l p for solutions of worm-like micelles 37 representing another class of self-assembling semiflexible objects. The occurrence of G ∼ ω 3/4 has also been observed for F-actin solutions.…”

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