Universal Yield Stress Equation Research Articles

A universal yield stress equation for electrorheological fluids

In this study, we investigate the universality of the yield stress [τyE0, where E0 is electric field strength] for examining electrorheological (ER) fluids both experimentally and theoretically. We found that the published experimental data for the yield stress of ER fluids for various materials and measurement conditions obey a yield stress scaling equation. In other words, the ER yield stress data in the literature collapse onto a universal correlation: τ̂=1.313Ê3/2tanhÊ using scaled variables τ̂≡τyE0/τyEc and Ê≡E0/Ec. Here, Ec is critical electric field strength. Although this expression is attractive for experimentalists, this empirical equation has not been derived from first principles. We introduce a mesoscopic elementary region concept and justify this universal correlation for the first time. We decompose the ER system into a finite number of elementary regions and introduce “glueons,” which adhere to neighboring elementary regions resulting in fibrillary structures. We investigated the limiting case when the elementary region size is reduced to zero (continuum limit) and used a reaction-diffusion model to calculate glueon concentration. In modeling the reaction term (generation of glueons), we used a linear model by recognizing that the electric field activates glueons, i.e., the number of glueons increases as the electric field strength increases. In our preliminary study, we were able to justify a universal correlation by solving the glueon concentration equation using a simple geometry. The novelty of this work is the development of universality for the ER yield stress and derivation of a universal scaling equation.

Polyaniline coated ZnFe2O4 microsphere and its electrorheological and magnetorheological response

Magnetic zinc ferrite particles synthesized by the solvothermal method were coated with conductive polyaniline, and their electro- and magneto-responsive smart fluid behaviors were investigated. Both size and morphology of the produced particles were identified by SEM and TEM. Their chemical composition and crystal faces were analyzed by FT-IR and X-ray diffraction, respectively. The synthesized particles were suspended in silicone oil at 5 vol%, and their electro- and magneto-responses were scrutinized using a rotation rheometer. In an electric field, the flow curve was fitted smoothly to the CCJ model, and the yield stress showed an exponential value of 1.5. In contrast, an exponential value of 1.0 was observed for the yield stress in a magnetic field. • Core-shell structured ZnFe 2 O 4 /PANI microspheres were synthesized. • Aniline monomer was adsorbed onto ZnFe 2 O 4 surface and polymerized via oxidation polymerization. • ER fluid based on ZF/PANI particles was prepared. • Different yield stresses of EMR fluid were correlated with universal yield stress equation.

Fabrication and magnetic stimuli-response of polydopamine-coated core–shell structured carbonyl iron microspheres

Soft magnetic carbonyl iron (CI) for application to magnetic stimuli-responsive smart materials in an external magnetic field normally implies severe sedimentation problems because of the density imbalance between the CI particles and the dispersed medium. As a new method of ameliorating this problem, CI/polydopamine (PDA) composite particles with core–shell structure were synthesized via an oxidative self-polymerization process, bringing into an account of the coating efficiency of the PDA. Surface morphology of the CI/PDA composite particles was characterized by scanning electron microscopy, while Fourier transform infrared spectroscopy, X-ray energy-dispersive spectroscopy, and vibrating sample magnetometry were adopted to measure the chemical composition, weight and atomic percentages, and magnetic properties of the fabricated composites. The magnetic stimuli-response of their magnetorheological (MR) properties was examined by using a rotational rheometer at various magnetic field strengths and compared with pristine CI-particle-based MR fluid. The measured dynamic yield stress was fitted to a universal yield stress equation well. The sedimentation properties of the CI/PDA-composite-based MR fluid were further examined by a Turbiscan™. In addition, the anti-corrosion characteristic of these particles was also investigated.

Yield stress analysis of 1D calcium and titanium precipitate-based giant electrorheological fluids

1D calcium and titanium composite nanorods synthesized were applied as electrorheological (ER) active materials with extremely high static yield stresses, i.e., giant ER effect. The yield stress of this giant ER fluid was analyzed using a new universal yield stress scaling equation in the form of the modified Bessel functions with two different limiting behaviors in a low and high electric field region. The universal yield stress equation collapsed the yield stress data onto a single curve.

Smart monodisperse polystyrene/polyaniline core–shell structured hybrid microspheres fabricated by a controlled releasing technique and their electro-responsive characteristics

We synthesized core/shell structured monodisperse semi-conducting polystyrene/polyaniline (PS/PANI) composite microspheres, and studied their electro-responsive electrorheological (ER) performance under an applied electric field strength when dispersed in silicone oil. An over-layer of the conducting PANI is formed by a controlled releasing process of the aniline pre-adsorbed on the PS seed latex without any surface modification, in which the PS seed microspheres were readily prepared by a dispersion polymerization method. The PS microspheres are observed to be regularly encapsulated with PANI from the morphology test. The ER behaviors of the hybrid microspheres are characterized using a rotational rheometer equipped with a high voltage supplier. The yield stress and flow response as a function of shear rate under certain electric field strengths are investigated using the universal yield stress equation and the Cho–Choi–Jhon model of rheological equation of state, respectively. The relaxation time and achievable polarizability of the fluid from its dielectric analysis were also found to be well correlated with the ER performance of the ER fluid.

Silica nanoparticle decorated polyaniline nanofiber and its electrorheological response

We fabricated polyaniline nanofibers (PANIFs) with an average diameter of 350 nm through an interfacial polymerization by using dodecylbenzylsulfate acid as a dopant, and then examined their electrorheological (ER) characteristics. Silica modification was carried out in ethanol/water solution via a modified Stober method, and successful location of the silica nanoparticles on the surface of PANIF was confirmed by both scanning electron microscope (SEM) and transmission electron microscope (TEM) images. Thermogravimetric analysis (TGA) showed enhanced thermostability of the modified nanofibers. ER tests including flow curve and amplitude/frequency sweeps, which were performed by a rotational rheometer, demonstrated that the nanosilica modified PANIF exhibits higher ER effect than pure PANIF. In addition, the resultant flow curves are fitted well by Cho–Choi–Jhon model rather than Bingham model, while the yield stresses of both ER fluids versus electric field strengths are fitted well into a single line by the universal yield stress equation.

Comment on “Universal yield stress equation for transient response of zeolite based electrorheological fluid”

We comment on the transient process of an electrorheological (ER) fluid under square-wave electric field excitation by analyzing its electric field-induced stable shear stress at a different shear rate. Using a critical electric field in the ER system, we find that the universal yield stress equation collapses the reported experimental data onto a single curve very well.

Electrorheology of a mesoporous silica having conducting polypyrrole inside expanded pores

A pore-expanded mesoporous silica (MCM-41-E) having particles of conducting polypyrrole (PPY) included inside its uniformly aligned one-dimensional channels was prepared, and their electrorheological (ER) characteristics when dispersed in a silicone oil were investigated. Both N 2-adsorption isotherm and SEM images were employed to confirm the successful formation of PPY/MCM-41-E nanocomposite. The XRD also provided an additional information on the properties of the synthesized nanocomposite material. The nanocomposite showed typical ER characteristics. Shear stress curve was more accurately described by using the rheological constitutive equation (CCJ model) we proposed compared with the Bingham fluid model. Yield stress which increases with applied electric field strength was analyzed based on the universal yield stress equation we suggest as a function of applied electric field strength. It was found that the universal yield stress equation collapses these data onto a single curve well in the case of PPY/MCM-41-E nanocomposite based ER fluid.

Comment on: Preparation, microstructure, and electrorheological property of nano-sized TiO2 particle materials doped with metal oxides

We comment on the shear stresses of recently reported Na-doped, Zr-doped, Al-doped, and Ce-doped TiO2-based electrorheological (ER) suspensions under applied electric strengths. Using deduced critical electric-field strength and additional scaled parameter, we found that the shear stresses could be analyzed using the universal yield stress equation, collapsing the data of Na-doped, Zr-doped, Al-doped, and Ce-doped TiO2 ER fluids onto a single curve

Organic/inorganic hybrid of polyaniline/BaTiO3 composites and their electrorheological and dielectric characteristics

AbstractBarium titanate (BaTiO3) inorganic particles which possess large electronic resistance and excellent dielectric properties were employed to synthesize conducting polyaniline (PANI)/BaTiO3 composites via an in situ oxidative polymerization, since conducting PANI/inorganic composites have been considered as a superior candidate of electrorheological (ER) fluids because of their physical properties, unique structure, and the combined merits of the two phases. The influence of the fraction of BaTiO3 particles in the as‐synthesized composites on the physical properties (morphology and crystal structure) and the ER behaviors were examined. Yield stress data obtained were analyzed based on the universal yield stress equation as a function of applied electric field and it was found that the universal yield stress equation collapses these data onto a single curve independent of BaTiO3 particle concentration. Their shear stresses under an applied electric field were also found to be fitted well with the Cho–Choi–Jhon model. In addition, the investigated dielectric spectra were found to be useful to interpret the differences in the ER performances for the PANI/BaTiO3 composite based ER fluids. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Comment on ‘Two roles of guest and crosslinked degree on hydrosoluble β-cyclodextrin polymer electrorheological fluids’ by Z. Gao and X. Zhao

Comments on the recent studies of electrorheological (ER) properties of hydrosoluble β-cyclodextrin polymer based ER fluids are given based on the analysis of their yield stress data as a function of applied electric field strengths. Using our previously reported universal yield stress equation and critical electric field strengths deduced, it is found that we can collapse their data into a single curve.

Comment on “An enhanced polarization mechanism for the metal cations modified amorphous TiO2 based electrorheological materials” by Qing Wu, Bin Yuan Zhao, Chen Fang and Ke Ao Hu

Comments on a recent article on an enhanced polarization mechanism for the metal cations modified amorphous TiO2 based electrorheological materials are presented, based upon an examination of the yield stress, which is a function of electric-field strength, of the materials. Using the deduced critical electric-field strengths, we find that the universal yield stress equation proposed collapses the data given by Qing Wu, Bin Yuan Zhao, Chen Fang, Ke Ao Hu, Eur. Phys. J. E 17, 63 (2005), onto a single curve.

Comment on “Preparation and electrorheological properties of triethanolamine-modified TiO 2”

Comments on the recent report of electrorheological (ER) properties of an organic modified titanium dioxide with considerably high yield stress are given based on the analysis of its yield stress data as a function of applied electric field strengths. Using our previously reported universal yield stress equation and critical electric field strengths deduced, it is found that we can collapse their data onto a single curve.

Comment on “Synthesis and electrorheological characterization of polymer containing amino and carboxy groups”

The comments for the recent article on electrorheological (ER) characterization of polymer containing amino and carboxy groups based ER fluids are given by analyzing its extrapolated yield stress data as a function of electric field strengths. Using the critical electric field strengths deduced, we found that the universal yield stress equation collapses their data onto a single curve.

Comment on “Preparation and electrorheological property of rare earth modified amorphous Ba xSr 1− xTiO 3 gel electrorheological fluid”

The comments on the recent results on electrorheological (ER) property of rare earth modified amorphous barium strontium titanate gel based ER fluid are given via analysis of its dynamic yield stress data as a function of applied electric field strengths. Using our previously reported universal yield stress equation, we obtained the critical electric field strength and collapsed their data onto a single curve.

Comment on “Preparation and electrorheological property of alkaline earth metal compounds modified amorphous TiO2 electrorheological fluid”

Comments on recent studies of electrorheological (ER) characteristics of alkaline earth metal compounds-modified amorphous TiO 2 based ER fluid are made based on the analysis of its yield stress data as a function of applied electric field strengths. It is found that our universal yield stress equation collapses their data onto a single curve.