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[Display omitted] The elastic contribution to the fluid dynamics of wormlike micellar solutions makes these fluids unique due to the distinctive self-assembled micellar network formed by tubular micelles. Measured mesoscopic scales of the micellar network related to the degree of entanglement can give guidelines for understanding the origin of elastic forces and their effect on rheological response. Different experiments were made as flow curves, rotating the internal or external cylinder in a Couette geometry, small and large oscillatory shear tests, and linear shear banding observations, all of them to determine how elastic forces modify the rheological behavior in systems made of different ratios of hexadecyltrimethylammonium bromide (CTAB)/sodium salicylate (NaSal) and different ratios of CTAB/NaNO 3. Diffusive wave spectroscopy micro-rheology was also performed to measure the mean square displacements of microspheres embedded in the micellar fluids to obtain their high-frequency viscoelastic spectra. With this information, the entanglement index κ , the ratio of the total contour of the micelles to the entanglement length, was estimated and correlated with the rheological behavior. The entanglement index is a valuable piece of information to understand the origin of the contribution of the elastic forces from a molecular point of view on the fluid dynamics of wormlike micelle solutions. [ABSTRACT FROM AUTHOR]

We derive explicit analytical expressions for the recurrence relations using the analytical matrix method for frequency response and the Bautista-Manero-Puig model for complex fluids. The BMP model is derived from the Extended Irreversible Thermodynamics formalism and has been shown to be useful in predicting the complex rheological behavior of self-associative systems. All harmonics of the alternating normal and shear stresses in oscillatory shear with various amplitude oscillatory regimes (AOS) can be calculated analytically, i.e., small amplitude oscillatory shear (SAOS), medium amplitude oscillatory shear (MAOS), and large amplitude oscillatory shear (LAOS). We show that incorporating the effects of the first and second normal stress differences for all AOS regimes leads to the emergence of higher harmonics. We establish the limits between the different AOS regimes based on criteria suggested by the analytical method. For some typical systems, such as CTAB-NaSal, we found a satisfactory quantitative agreement with the measured behavior of AOS. [ABSTRACT FROM AUTHOR]

Oscillatory shear testing, used to characterize the viscoelastic response of soft materials, is often divided into small, medium, and large amplitude oscillatory shear (SAOS, MAOS, and LAOS) regions. SAOS is a common test that gives us a unified analysis and interpretation of linear viscoelastic behavior, whereas understanding MAOS and LAOS is still an active area of research. While numerous mathematical techniques have been proposed, a consensus interpretation is still missing. Recently, our understanding of nonlinear behavior in the LAOS regime has been developed using iterative recovery tests. Recovery rheology decomposes the strain into two components, allowing an unambiguous interpretation of the nonlinear behavior in terms of sequences of recoverable and unrecoverable processes. In this work, we revisit the MAOS material functions for polyvinyl alcohol-borax hydrogel and worm-like micelles using recovery rheology. We show that two mathematical formalisms, the Chebyshev and sequence of physical processes analyses, provide competing physical interpretations when they are derived from the total strain, but provide unified interpretations when describing the decomposed strains. We, therefore, show that what has often been treated as a mathematical problem can instead be solved experimentally by acknowledging the extra information provided by recovery rheology. [ABSTRACT FROM AUTHOR]

For over 25 years, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) techniques have been used to study materials under mechanical deformation. Collectively, these methods are referred to as Rheo‐NMR. In many cases, it provides spatially and temporally resolved maps of NMR spectra, intrinsic NMR parameters (such as relaxation times), or motion (such as diffusion or flow). Therefore, Rheo‐NMR is complementary to conventional rheological measurements. This review will briefly summarize current capabilities and limitations of Rheo‐NMR in the context of material science and food science in particular. It will report on recent advances such as the incorporation of torque sensors or the implementation of large amplitude oscillatory shear and point out future opportunities for Rheo‐NMR in food science. [ABSTRACT FROM AUTHOR]

Two instantaneous dimensionless numbers that act as Deborah and Weissenberg numbers are introduced to diagnose flow conditions for transient nonlinear rheology. The utility of the new numbers is demonstrated on the steady alternating large amplitude oscillatory shear response of a colloidal Ludox glass, the soft glassy rheology model, and a viscoelastic wormlike micelle solution. Complex nonlinear trajectories through Pipkin space are observed, from which it is concluded that large amplitude oscillatory shear represents a range of distinct flow types. These results indicate that the observation time may change significantly during a period of oscillation. The complex trajectories observed for all three systems go from close to one axis to close to the other and back in quick succession. Rather than existing in the dominant central area that Pipkin originally marked as "?", LAOS may simply be the way by which the axes of Pipkin space are dynamically linked. [ABSTRACT FROM AUTHOR]

Stress relaxation from a step strain test provides important information about constituent dynamics, but if a material has experienced a complex shear history, the underlying physics is not straightforward to access. We use recovery rheology and rheo‐small‐angle neutron scattering to probe the nonlinear dynamics of an entangled wormlike micelle solution by applying step strains after complex shear histories enforced by large‐amplitude oscillatory shear (LAOS) flow. We show that a universal relaxation modulus can be obtained from step strain tests with complex shear histories, as long as the modulus is defined in terms of the recoverable strain. The shear and normal stresses, as well as the alignment of micellar Kuhn segments, are shown to be positively correlated with the recoverable strain. We identify re‐entanglement of polymeric chains after cessation of LAOS and show that this process occurs over the same timescales as linear‐regime stress relaxation. This work, therefore, lays the foundation of how to accurately probe out‐of‐equilibrium rheology in a consistent manner. [ABSTRACT FROM AUTHOR]

Understanding how microscopic rearrangements manifest in macroscopic flow responses is one of the central goals of nonlinear rheological studies. Using the sequence-of-physical-processes framework, we present a natural 3D structure–rheology space that temporally correlates the structural and nonlinear viscoelastic parameters. Exploiting the rheo-small-angle neutron scattering (rheo-SANS) techniques, we demonstrate the use of the framework with a model system of polymer-like micelles (PLMs), where we unveil a sequence of microscopic events that micelles experience under dynamic shearing across a range of frequencies. The least-aligned state of the PLMs is observed to migrate from the total strain extreme toward zero strain with increasing frequency. Our proposed 3D space is generic, and can be equally applied to other soft materials under any sort of deformation, such as startup shear or uniaxial extension. This work therefore provides a natural approach for researchers to study complex out-of-equilibrium structure–rheology relationships of soft materials. [ABSTRACT FROM AUTHOR]