Revealing importance of particles' surface functionalization on the properties of magnetic alginate hydrogels.

Iron/silica core-shell microparticles (IMPs) were functionalized by different functional groups including amine, glycidoxy, phenyl, and thiocyanate. Many of the IMPs modifications are reported for the first time. The resulting surface chemistry turned out to affect the properties of magnetic alginate hydrogels fabricated from sodium alginate and dispersed IMPs.

Multi-ionic effects on energy production based on double layer expansion by salinity exchange.

It has been recently shown that the free energy change upon salinity mixing in river mouths can be harvested taking advantage of the fact that the capacitance of charged solid/liquid interfaces (electrical double layers, EDLs) depends strongly on the ionic composition of the liquid medium. This has led to a new generation of techniques called Capmix technologies, one of them (CDLE or capacitive energy extraction based on DL expansion) based precisely on such dependence. Despite the solution composition playing a crucial role on the whole process, most of the research carried out so far has mainly focused on pure sodium chloride solutions.

How nonmagnetic particles intensify rotational diffusion in magnetorheological fluids.

In this work we propose a mechanism to explain the enhancement of the magnetic-field-induced yield stress when nonmagnetic particles are added to magnetic particulate suspensions, i.e., two-component suspensions.

Dynamic characterization of extremely bidisperse magnetorheological fluids.

In this work, we investigate the stability and redispersibility of magnetorheological fluids (MRFs). These are disperse systems where the solid is constituted by ferro- or ferri-magnetic microparticles. Upon the application of external magnetic field, they experience rapid and reversible increases in yield stress and viscosity.

Steric repulsion as a way to achieve the required stability for the preparation of ionic liquid-based ferrofluids.

With this work we would like to emphasize the necessity of steric repulsion to stabilize novel ionic liquid-based ferrofluids. For this purpose, we prepared a suspension of magnetite nanoparticles coated with a double layer of oleic acid, dispersed in 1-ethyl-3-methylimidazolium ethylsulphate ([EMIM][EtSO(4)]). For comparison, a suspension of bare magnetite nanoparticles in [EMIM][EtSO(4)] was also prepared.

Measurement and interpretation of electrokinetic phenomena.

In this report, the status quo and recent progress in electrokinetics are reviewed. Practical rules are recommended for performing electrokinetic measurements and interpreting their results in terms of well-defined quantities, the most familiar being the zeta-potential or electrokinetic potential. This potential is a property of charged interfaces and it should be independent of the technique used for its determination.

Nonstationary electro-osmotic flow in closed cylindrical capillaries. Theory and experiment.

Both from the experimental and theoretical viewpoints it is of fundamental importance to know precisely which are the fluid flow characteristics in a (cylindrical, say) closed cell under the action of an externally applied electric field, parallel to the cell axis. This is so because in many cases the experimental determination of the electrophoretic mobility of dispersed particles is carried out in closed cells, whereby the motion of the particles in the laboratory reference system is the result of the superposition of their electrophoretic migration plus the liquid motion with respect to the cell. This makes it of utmost importance to analyze the above-mentioned fluid and particle movements.

Study of the colloidal stability of concentrated bimodal magnetic fluids.

In this paper, we describe an investigation of the stability and sedimentation behavior of moderately concentrated suspensions of extremely bimodal magnetite particles, including micro- (diameter 1450 nm) and nano- (diameter 8 nm) units. An original method is used, based on the determination of the time dependence of the inductance of a coil surrounding the suspensions. The method proves to be very useful for the determination of the volume fraction of magnetic material in the sensed volume.

Structural explanation of the rheology of a colloidal suspension under high dc electric fields.

In this work we describe the electrorheology of suspensions consisting of hematite (alpha-Fe2O3) particles dispersed in silicone oil in the presence of large dc electric fields. If an electric field pulse is applied to the systems, it is possible to estimate the time that the electrorheological (ER) fluid takes to reach its final microstructure in the presence of the field. Our results indicate that response times of several seconds are typical, and that this time decreases with the field strength.

Nonstationary electroosmotic flow in closed cylindrical capillaries.

A theoretical model of the EOF and hydrodynamic flow in wide closed cylindrical capillaries, after the application of a stepwise voltage, is developed. Analytical expressions have been obtained as a sum of the solutions for the direct flow and backflow in both periodical and aperiodical regimes with arbitrary pulse/pulse or pulse/pause durations and amplitudes. The numerical analysis, performed for a few types of periodical and aperiodical regimes, shows the qualitative peculiarities of the liquid velocity profiles and its displacement for different numbers of pulses.

Nonstationary electroosmotic flow in open cylindrical capillaries.

A theoretical model of the EOF established in a wide capillary after the application of a stepwise voltage has been developed. Both periodical and aperiodical flow regimes were studied with arbitrary pulse/pulse or pulse/pause durations and amplitudes. The numerical analysis performed for a few types of periodical regimes showed the peculiarities of the profiles of liquid velocity and its displacement both for the transition to the stationary regime and for the quasi-stationary periodical and aperiodical regimes.

Preparation and sedimentation behavior in magnetic fields of magnetite-covered clay particles.

This work is devoted to the preparation of magnetite-covered clay particles in aqueous medium. For this purpose, magnetite nanoparticles were synthesized by a coprecipitation method. These magnetic particles are adhered to sodium montmorillonite (NaMt) particles in aqueous suspensions of both materials, by appropriate control of the electrolyte concentrations.

Stability and magnetic characterization of oleate-covered magnetite ferrofluids in different nonpolar carriers.

This work describes the preparation and stability evaluation of suspensions consisting of hydrophobic magnetite nanoparticles dispersed in different organic solvents. The ferrite particles are covered by a shell of chemisorbed oleate ions following a procedure that is described in detail. The oleate-covered particles were dispersed in different organic solvents with dielectric constants, epsilon(r), ranging between 1.

Polarization of the Electrical Double Layer. Time Evolution after Application of an Electric Field.

Electrophoresis is one of the electrokinetic phenomena most widely investigated, both from a fundamental point of view and as a research tool in academia and industry. However, the dependence between electrophoretic mobility and zeta potential is, in a general case, far from simple, because of the many physical processes involved. In this work, we first describe qualitatively and (in some cases) quantitatively the time behavior of the dipole moment induced in the electrical double layer by an applied electric field.

Rheological and Electrokinetic Properties of Sodium Montmorillonite Suspensions.

In this article, we describe the rheology of Na montmorillonite suspensions as a function of pH, at constant ionic strength. The observed behavior is discussed quantitatively in terms of the potential energy of interaction between particles, keeping in mind the anisotropic nature of clay particles. The extended DLVO model that includes electrostatic, van der Waals, and polar acid-base contributions to the total energy is used.

Dynamics of the Electric Double Layer: Analysis in the Frequency and Time Domains.

No rigorous theory of electrokinetic phenomena is conceivable without properly accounting for double layer polarization under the action of external fields. Since processes leading to such polarization need a finite time to develop, an analysis of the behavior of the quantities of interest (potential and ion concentration profiles, particle or fluid velocity, and so on) as a function of time should be extremely illustrative. In this work, we analyze how those quantities evolve in the nanosecond to microsecond time range after the application of an electric field.

Deposition of Colloidal Zinc Sulfide on Glass Substrate.

The effect of colloidal forces involved in the deposition of spherical zinc sulfide colloidal particles on a packed bed of glass has been studied. Experiments were performed by pumping a suspension of monodisperse colloidal ZnS particles through a cylindrical plug of ground glass, and by continuous determination of the outgoing suspension concentration. The flux density of adhered particles, jexp (number of particles deposited per unit time and unit surface area of glass collector), decreased with both pH and ionic strength of the aqueous electrolyte solution.

Surface Chemical Analysis and Electrokinetic Properties of Synthetic Spherical Mixed Zinc-Cadmium Sulfides.

In this work, we analyze the surface and bulk chemical composition, as well as the crystal structure, of colloidal spherical particles of Zn-Cd mixed sulfides of different Zn/Cd ratios. The particles were obtained by precipitation from solution according to the method described by Wilhelmy and Matijevic [Colloids Surfaces 16, 1 (1985)]. Transmision electron microscopy of the particles show that their average diameter ranges from 50-60 nm (when the synthesis is carried out at 50degreesC) up to 150-200 nm (for a temperature of 70degreesC).

Expanding forces in aqueous outflow pathways of a nonaccommodating mammal: an approach via comparative dynamic morphology.

Six dog eyes were fixed by intracameral perfusion of fixative at pressures of 0, 5, 10, 15, 20, and 25 cm of water. Eight dog eyes were fixed after the injection in both ocular chambers of a number of cholinergic agents, either singly or in combination. Under the effect of miotics and under increased ocular pressure, the aqueous pathways expand.

Effect of amino acids on the stability properties of nitrofurantoin suspensions. Flocculation and redispersion compared with interaction energy curves.

The influence of the addition of amino acids, lysine, alanine and glutamic acid on the properties of nitrofurantoin suspensions was investigated. Flocculation and redispersability was investigated, taking into account the electrical properties of the nitrofurantoin/solution interface. We conclude that lysine and glutamic acid, but not alanine, would be suitable amino acids for control of the stability of nitrofurantoin suspensions.

Role of cameral mucous gel in primary narrow angle and closed angle glaucoma: a pathogenic clue.

The cameral mucous gel (CMG) has been described as a layer of glycoprotein-enriched hyaluronic acid lining the anterior surface of the iris, covering the trabecular meshwork, and spreading over the posterior surface of the cornea. The CMG is thought to exert a colloid-osmotic effect on the hydrostatic forces involved in the circulation of the aqueous humour which may help our understanding of the pathophysiology of open angle and angle closure glaucomas. The CMG was precipitated in two normal human eyes, one with an artificially shortened anterior chamber and the other with an open chamber.

A study of the electrokinetic and stability properties of nitrofurantoin suspensions. II: Flocculation and redispersion properties as compared with theoretical interaction energy curves.

The stability and redispersion properties of nitrofurantoin dispersions are experimentally studied using simple but reproducible techniques. Solutions of different electrolyte concentrations and pH values are employed as dispersing media. The pH appears to be a determinant factor in the properties studied.

A study of the electrokinetic and stability properties of nitrofurantoin suspensions. I: Electrokinetics.

An experimental investigation is described of the electrokinetic properties of nitrofurantoin. The experiments are based on measurements of electrophoretic mobility in suspensions of this drug and the calculation of its zeta potential (zeta) following two different procedures. A simple mechanism is proposed for explaining the sign of the surface charge of nitrofurantoin and its increase with the pH of the medium.

A network thermodynamic method for numerical solution of the Nernst-Planck and Poisson equation system with application to ionic transport through membranes.

Simple techniques of network thermodynamics are used to obtain the numerical solution of the Nernst-Planck and Poisson equation system. A network model for a particular physical situation, namely ionic transport through a thin membrane with simultaneous diffusion, convection and electric current, is proposed. Concentration and electric field profiles across the membrane, as well as diffusion potential, have been simulated using the electric circuit simulation program, SPICE.