Dynamic rheology of sphere- and rod-based magnetorheological fluids
J. de Vicente, J. P. Segovia-Gutierrez, E. Andablo-Reyes, F. Vereda, and R. Hidalgo-Alvarez
The effect of particle shape in the small amplitude oscillatory shear behavior of magnetorheological (MR) fluids is investigated from zero magnetic field strengths up to 800 kA/m. Two types of MR fluids are studied: the first system is prepared with spherical particles and a second system is prepare ... [J. Chem. Phys. 131, 194902 (2009)] published Mon Nov 16, 2009.
Dielectrophoretic and electrophoretic force analysis of colloidal fullerenes in a nematic liquid-crystal medium
Anoop Kumar Srivastava, Miyoung Kim, Sung Min Kim, Mi-Kyung Kim, Kyu Lee et al.
This research focuses on the electrokinetic motion of fullerenes suspended in liquid crystal host medium, which are investigated in the homogeneously aligned nematic liquid crystal cells driven by in-plane field. We investigated the effect of electrophoretic and dielectrophoretic forces and related ... [Phys. Rev. E 80, 051702 (2009)] published Mon Nov 16, 2009.
Ordering of a lamella-forming fluid near an interface
Andrew B. Croll, An-Chang Shi, and Kari Dalnoki-Veress
By using wedged thin films, we have measured the effect of interfaces on the ordering of an anisotropic fluid in real space. Symmetric diblock copolymers can form an ordered lamellar fluid, and the preference of the substrate for one of the blocks can induce order well into the disordered bulk phase ... [Phys. Rev. E 80, 051803 (2009)] published Wed Nov 11, 2009.
Quenched random disorder and x-ray scattering in smectic elastomers
L. T. Witkowski and E. M. Terentjev
In this work we examine layer fluctuations in a smectic elastomer with quenched random disorder induced by crosslinks. The system is analyzed in a continuum model and crosslinks are introduced as a random field in a macroscopic picture. In the case of small deformations and replica symmetry the inte ... [Phys. Rev. E 80, 051701 (2009)] published Tue Nov 10, 2009.
Structure and rheology of SiO nanoparticle suspensions under very high shear rates
J. Chevalier, O. Tillement, and F. Ayela
High shear rate experiments have been performed with capillary microviscometers onto SiO nanoparticles dispersed in alcohol (so-called nanofluids). The aim of these experiments was to investigate the processes of aggregation and dislocation of the nanoparticles in a shear flow under perikinetic and ... [Phys. Rev. E 80, 051403 (2009)] published Fri Nov 6, 2009.
Quick Clay and Landslides of Clayey Soils
Asmae Khaldoun, Peder Moller, Abdoulaye Fall, Gerard Wegdam, Bert De Leeuw et al.
We study the rheology of quick clay, an unstable soil responsible for many landslides. We show that above a critical stress the material starts flowing abruptly with a very large viscosity decrease caused by the flow. This leads to avalanche behavior that accounts for the instability of quick clay s ... [Phys. Rev. Lett. 103, 188301 (2009)] published Wed Oct 28, 2009.
Mathematical Modeling, Analysis, and Design of Magnetorheological (MR) Dampers
Weng Wai Chooi and S. Olutunde Oyadiji
Most magnetorheological (MR) fluid dampers are designed as fixed-pole valve mode devices, where the MR fluid is forced to flow through a magnetically active annular gap. This forced flow generates the damping force, which can be continuously regulated by controlling the strength of the applied magne ... [J. Vib. Acoust. 131, 061002 (2009)] published Tue Oct 27, 2009.
Storage shear modulus of columnar structure formed in an immiscible polymer blend under electric fields
Kohei Aida, Yang Ho Na, Tomoyuki Nagaya, and Hiroshi Orihara
Oscillatory measurements of a columnar structure were performed, which was formed in an immiscible polymer blend subjected to an electric field. The formation process was observed through a confocal scanning laser microscope and the structure for the measurements was confirmed to be well defined. Th ... [Phys. Rev. E 80, 041807 (2009)] published Mon Oct 26, 2009.
Yield Stress and Shear Banding in Granular Suspensions
Abdoulaye Fall, Francois Bertrand, Guillaume Ovarlez, and Daniel Bonn
We study the emergence of a yield stress in dense suspensions of non-Brownian particles by combining local velocity and concentration measurements using magnetic resonance imaging with macroscopic rheometric experiments. We show that the competition between gravity and viscous stresses is at the ori ... [Phys. Rev. Lett. 103, 178301 (2009)] published Fri Oct 23, 2009.
Conformational free energy of melts of ring-linear polymer blends
Gopinath Subramanian and Sachin Shanbhag
The conformational free energy of ring polymers in a blend of ring and linear polymers is investigated using the bond-fluctuation model. Previously established scaling relationships for the free energy of a ring polymer are shown to be valid only in the mean-field sense, and alternative functional f ... [Phys. Rev. E 80, 041806 (2009)] published Wed Oct 21, 2009.
Experimental evidence for reversible zippering of chains in magnetic nanofluids under external magnetic fields
Junaid M. Laskar, John Philip, and Baldev Raj
We study the time-dependent transmitted intensity and the scattered pattern from magnetic nanofluids at constant ramping of uniform external magnetic field. The nanofluid used is the dispersion of magnetite particles with an average diameter of 6.5 nm with a protective surfactant coating. We observe ... [Phys. Rev. E 80, 041401 (2009)] published Fri Oct 16, 2009.
Two-particle microrheology at oil-water interfaces
Chih-yuan Wu, Yanmei Song, and Lenore L. Dai
We have explored and validated two-particle (2P) microrheology at polydimethylsiloxane (oil)-water interfaces using confocal laser scanning microscopy. The loss and storage moduli of the oil-water interfaces as a function of frequency are quantified using different tracer particles. In contrast to o ... [Appl. Phys. Lett. 95, 144104 (2009)] published Wed Oct 7, 2009.
Microviscoelasticity of adhesive hard sphere dispersions: Tracer particle microrheology of aqueous Pluronic L64 solutions
Christopher J. Kloxin and John H. van Zanten
DWS-based tracer particle microrheology is demonstrated to be a useful way to study the dynamics of aqueous Pluronic L64 solutions, which is viewed as a model adhesive hard sphere (AHS) system. The short-time dynamics of aqueous Pluronic L64 solutions indicate a purely hydrodynamic high frequency mi ... [J. Chem. Phys. 131, 134904 (2009)] published Wed Oct 7, 2009.
Reorientation effect and electrical current in a weakly anchored nematic cell
R. Teixeira de Souza, M. M. A. de Jesus, J. C. Dias, and L. R. Evangelista
A nematic cell subjected to a large electric field undergoes a molecular reorientation that affects the electrical current flowing through it. To analytically establish the dependence of the current on the applied voltage, the cell is considered as parallel of resistance, R(t), and capacitance, C(t) ... [Phys. Rev. E 80, 041702 (2009)] published Wed Oct 7, 2009.
Comment on Resolving the Mystery of the Chain Friction Mechanism in Polymer Liquids
K. L. Ngai, D. J. Plazek, and C. M. Roland
A Comment on the Letter by Alexei P. Sokolov and Kenneth S. Schweizer, Phys Rev. Lett. 102, 248301 (2009). The authors of the Letter offer a Reply. ... [Phys. Rev. Lett. 103, 159801 (2009)] published Mon Oct 5, 2009.
Sokolov and Schweizer Reply:
Alexei P. Sokolov and Kenneth S. Schweizer
A Reply to the Comment by K. L. Ngai, D. J. Plazek, and C. M. Roland. ... [Phys. Rev. Lett. 103, 159802 (2009)] published Mon Oct 5, 2009.
Shear thickening in colloidal dispersions
Norman J. Wagner and John F. Brady
The popular interest in cornstarch and water mixtures known as oobleck after the complex fluid in one of Dr. Seuss's classic children's books arises from their transition from fluid-like to solid-like behavior when stressed. The viscous liquid that emerges from a roughly 2-to-1 (by volume) combinati ... [Phys. Today 62, 27 (2009)] published Thu Oct 1, 2009.
Superhydrophobic surfaces reduce drag
Mark Wilson
Turbulent flows of a liquid along a wall experience frictional drag, a macroscopic phenomenon that strongly affects the efficiency, costs, and other parameters of countless engineering systemsfrom marine vessels to oil pipelines. The drag arises from shear stress, the rate per unit area of momentum ... [Phys. Today 62, 16 (2009)] published Thu Oct 1, 2009.
Topological analysis of polymeric melts: Chain-length effects and fast-converging estimators for entanglement length
Robert S. Hoy, Katerina Foteinopoulou, and Martin Kroger
Primitive path analyses of entanglements are performed over a wide range of chain lengths for both bead spring and atomistic polyethylene polymer melts. Estimators for the entanglement length N which operate on results for a single chain length N are shown to produce systematic O(1/N) errors. The ma ... [Phys. Rev. E 80, 031803 (2009)] published Tue Sep 29, 2009.
Interplay between Shear Loading and Structural Aging in a Physical Gelatin Gel
O. Ronsin, C. Caroli, and T. Baumberger
We show that the aging of the mechanical relaxation of a gelatin gel exhibits the same scaling phenomenology as polymer and colloidal glasses. In addition, gelatin is known to exhibit logarithmic structural aging (stiffening). We find that stress accelerates this process. However, this effect is def ... [Phys. Rev. Lett. 103, 138302 (2009)] published Tue Sep 22, 2009.
Elongational Flow of Blends of Long and Short Polymers: Effective Stretch Relaxation Time
Dietmar Auhl, Pierre Chambon, Tom C. B. McLeish, and Daniel J. Read
We study the onset of chain stretch and emergent extension hardening in the nonlinear rheological response of molten binary blends of long and short polymers. We predict that, upon dilution with short chains, the effective stretch relaxation time of the long chains initially increases in proportion ... [Phys. Rev. Lett. 103, 136001 (2009)] published Mon Sep 21, 2009.