Nonlinear Shear and Extensional Flow Dynamics of Wormlike Surfactant Solutions

Accepted for publication in JNNFM.Nonlinear shear and extensional flow dynamics of rheological properties of a wormlike micellar solution based on erucyl bis (2-hydroxyethyl) methyl ammonium chloride, EHAC, are reported here. The influences of surfactant (EHAC) and salt (NH4Cl) concentrations on the linear viscoelastic parameters are determined using small amplitude oscillatory shear experiments. The steady and time-dependent shear rheology is determined in a double gap Couette cell, and transient extensional flow measurements are performed in a Capillary Breakup Extensional Rheometer (CABER). In the nonlinear shear flow experiments, the micellar fluid samples show strong hysteretic behavior upon increasing and decreasing the imposed shear stress due to the development of shear-banding instabilities. The non-monotone flow curves of stress vs. shear rate can be successfully modeled in a macroscopic sense by using the single-mode Giesekus constitutive equation. The temporal evolution of the flow structure of the surfactant solutions in the Couette flow geometry is analyzed by instantaneous shear-rate measurements for various values of controlled shear-stress, along with FFT analysis. The results indicate that the steady flow bifurcates to a global time-dependent state as soon as the shear banding/hysteresis regime is reached. Increasing the salt/surfactant ratio or the temperature is found to stabilize the flow, as also confirmed by the decreasing values of anisotropy factor in the Giesekus model. Finally we have investigated the dynamics of capillary breakup of the micellar fluid samples in uniaxial extensional flow. The filament thinning behavior of the micellar fluid samples is also accurately predicted by the Giesekus constitutive equation. Indeed quantitative agreement between the experimental and numerical results can be obtained providing that the relaxation time of the wormlike micellar solutions in extensional flows is a factor of three lower than in shear flows.NSF, Schlumberger, and the Turkish Scientific and Technical Research Institut

Rheo-PIV of a shear-banding wormlike micellar solution under large amplitude oscillatory shear

We explore the behavior of a wormlike micellar solution under both steady and large amplitude oscillatory shear (LAOS) in a cone–plate geometry through simultaneous bulk rheometry and localized velocimetric measurements. First, particle image velocimetry is used to show that the shear-banded profiles observed in steady shear are in qualitative agreement with previous results for flow in the cone–plate geometry. Then under LAOS, we observe the onset of shear-banded flow in the fluid as it is progressively deformed into the non-linear regime—this onset closely coincides with the appearance of higher harmonics in the periodic stress signal measured by the rheometer. These harmonics are quantified using the higher-order elastic and viscous Chebyshev coefficients e [subscript n] and v [subscript n] , which are shown to grow as the banding behavior becomes more pronounced. The high resolution of the velocimetric imaging system enables spatiotemporal variations in the structure of the banded flow to be observed in great detail. Specifically, we observe that at large strain amplitudes (γ [subscript 0] ≥ 1), the fluid exhibits a three-banded velocity profile with a high shear rate band located in-between two lower shear rate bands adjacent to each wall. This band persists over the full cycle of the oscillation, resulting in no phase lag being observed between the appearance of the band and the driving strain amplitude. In addition to the kinematic measurements of shear banding, the methods used to prevent wall slip and edge irregularities are discussed in detail, and these methods are shown to have a measurable effect on the stability boundaries of the shear-banded flow.Spain. Ministerio de Educación y Ciencia (MEC) (Project FIS2010-21924-C02-02

Recent experimental probes of shear banding

Recent experimental techniques used to investigate shear banding are reviewed. After recalling the rheological signature of shear-banded flows, we summarize the various tools for measuring locally the microstructure and the velocity field under shear. Local velocity measurements using dynamic light scattering and ultrasound are emphasized. A few results are extracted from current works to illustrate open questions and directions for future research.Comment: Review paper, 23 pages, 11 figures, 204 reference

Mechanical and tribological properties of scrap rubber based composites reinforced with glass fiber, Al and TiO2

Scrap rubber/Epoxy composites reinforced with Aluminium, Glass Fibre (GF) and TiO2 particles were prepared and mechanical and tribological properties of these composites were investigated. Basically, these composites are aimed to use in automotive and aeronautics applications. A detail microstructure and matrix/reinforcement interface analyze was made by means of Scanning Electron Microscope (SEM) The wear performance of hard particles reinforced composites were evaluated. Quasi static and dynamic compression tests were carried out and damaged specimens were studied by SEM. The hardness (short test) values of the composites were reviewed related to the reinforcement elements, Glass Fibre-fiber and TiO2 added in the matrix

Study of influence of sic and al \u3c inf\u3e 2 o \u3c inf\u3e 3 as reinforcement elements in elastomeric matrix composites

Rubber is an important polymer type that is widely used due to its high and reversible deformability. Since the modulus and strength of neat rubber are low, an additional reinforcing phase is necessary for the use of rubber materials in practical applications. Rubber is generally reinforced with fibers, carbon black (CB), and silicates. In our study we also use carbon black as filler reinforcement but in order to increase the mechanical properties even more we have added different particles (SiC and Al2O3) in rubber based composites. In the frame of the common research project, NR/BR based composites with different curing systems were characterized with respect to their curing characteristics and mechanical properties. The cure characteristics of the rubber compounds were studied by using the Monsanto MDR 2000 rheometer. Microindentation test was used for studying the viscoelastic behaviour of the compounds. Addition of different reinforcing particles can improve certain properties of rubber blends, such as stiffness, vulcanisation rate and crosslink density