A Magnetooptical Effect in a Rotating Field in the Case of a Polymorphic Colloid

Magnetooptical methods are used to study particle polymorphism in colloids and suspensions. Electrooptical methods of studying disperse systems make it possible to determine the average value of the shape factor of colloidal particles approximated by ellipsoids of revolution. However, they do not enable one to solve the problem of the particle shape distribution in real disperse systems, because the orientation of particles in an electric field always depends on their size as well as shape. The use of a magnetic field makes it possible to create the conditions under which the orientation of particles is determined by their shape irrespective of the size.     

Magnetooptical phenomena in disperse systems in uniform linearly oriented magnetic fields

The theory of magnetooptical phenomena in disperse systems subjected to constant magnetic fields is outlined. A magnetooptical method is proposed for determining the magnetic characteristics and size distribution of particles in polydisperse colloidal solutions and suspensions. The magnetooptical properties of aqueous colloids of anisaldazine and acetoxybenzalazine are studied and the size distribution functions of dispersed particles are determined.     

Numerical methods for inverse problems in electrooptics of polydisperse colloids

In this paper we propose a new method for the determination of the distribution of electrical and geometrical particle parameters based on electrooptical experimental data. The electrooptical method leads to the solution of inverse ill-posed problems. The main equations for the determination of the distribution of particles on these parameters are presented. To find out the distribution functions from the electrooptical experimental data one has to solve the first-kind Fredholm integral equation corresponding to the problem under study. The proposed method of its solution is based on the penalty functions method. The results of modelling that let us compare the various numerical methods are presented.     

Structure of aqueous dispersions of Mg<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> nanotubes

Behavior of hydrosilicate nanotubes of composition Mg₃Si₂O₅(OH)₄ in aqueous dispersions was studied. Experiments devoted to observation of steady-state and relaxation electro-optical effects demonstrated that, irrespective of their initial concentration in water, nanotubes form stable bulk aggregates with weak anisotropy, rather than a homogeneous system of separate suspended nanosize cylinders.     

Electrooptical properties of aqueous suspensions of nickel hydrosilicate nanotubes

We present the results of our investigations of electrooptical effects that occur as a result of light scattering by an aqueous polydisperse system the disperse phase of which consists of nickel hydrosilicate nanotubes with a chrysotile structure. Multilayer nanotubes were synthesized by the hydrothermal method and had the composition Ni₃Si₂O₅. The dimensions of nanotubes were as follows: the length was 0.1–1 μm or more, the outer diameter was 10–15 nm, and the inner diameter was 3 nm. We have studied relative changes in the intensities of light transmitted and scattered by the suspension that were caused by the orientation of nanotubes in an external electric field. Experiments have been performed at different directions of the linear polarization of the incident and scattered light, different scattering angles, and different degrees of orientation of nanotubes along the field. These measurements allowed us to determine the magnitude of electrooptical effects, such as the conservative dichroism, the light scattering, and the influence of the orientation of nanotubes in the field on the intensity and degree of depolarization of light scattered by them. Curves of free relaxation of electrooptical effects and their field dependences allowed us to determine the distributions of nanotubes and their aggregates in the colloid over lengths and polarizability anisotropy values. The dependences of the degree of depolarization of the scattered radiation on the scattering angle and the relaxation dependences of electrooptical effects allowed us to characterize the aggregation stability of nanotubes in water.     

Effect of electric field on light scattering by aqueous colloids of diamond and graphite

We present the results of our experimental investigation of light scattering by polydisperse colloids of diamond and graphite. The scattering is studied at a random orientation of particles and in an external radiofrequency electric field, which orients particles along the strength. The average dimensions of particles in both colloids are close to each other and comparable with the wavelength of the incident light. The shape of particles and the optical and electrooptical properties of diamond and graphite colloids are significantly different. We analyze the polarization components of scattered light energy when the light incident on the colloids is linearly polarized. We show that the quadrupole light scattering by isotropic diamond particles has the main effect on angular dependences of depolarization of scattered light. For light scattering by anisotropic graphite particles, the depolarization of scattered light is mainly determined by a particular feature of the dipole scattering of particles. It is shown that, in both colloids, the orientational order of particles considerably reduces the depolarization of light scattered by particles. We show that relative changes in the intensity and depolarization of scattered light, which depend on the scattering angle and polarization direction of light, as well as on the parameters of particles, can be used as a measure of electrooptical effects observed in colloids.     

An Electrooptical Method for Studying the Coagulation of Nanodisperse Systems: Formation of Aggregates of Graphite Particles in Aqueous Electrolytes

Optics and Spectroscopy - We demonstrate that the electrooptical method can be used to study the coagulation of liquid nanodisperse systems, in particular, colloids and suspensions. Two...     

Stability of tungsten(VI) oxide dispersions in electrolyte solutions

The aggregation stability of tungsten oxide hydrosols is studied by the photometric and electrooptical methods. Coagulation thresholds determined in solutions of 1 : 1, 2 : 1, and 3 : 1 electrolytes obey the Schulze-Hardy rule. The coagulation is shown to occur by the barrier mechanism predominantly through adhering of small particles to large ones without considerable changes in the sizes of the latter.     

Relaxation of an electrooptical effect in colloids induced by a field of short pulses

The possibility of studying the size distribution of particles suspended in a liquid irradiated with short pulses of strong electric fields, which almost do not change the properties of the disperse system is considered. The particle size is varied from 10 to 1000 nm. Relaxation dependences of the optically anisotropy induced by such pulses are investigated. The relaxation curves of the induced electrooptical effect are shown to behave similarly to the relaxation curves of the effect in the system with completely oriented particles. For aqueous polydisperse systems of diamond, graphite, and palygorskit, whose particles significantly differ in shape and physicochemical properties, the relaxation dependences of the electrooptical effect induced by fields of different duration and amplitude are measured. The correlation coefficients between the relaxation dependences are calculated. If the field is sufficiently strong, the correlation coefficients remain close to unity for all the three systems studied irrespective of the duration of the field pulse. This indicates that these curves are similar and that short powerful pulses can be used for determining the size distribution of particles in nanodisperse systems.     

Electrooptic properties of aqueous suspensions of nanotubes based on magnesium hydrosilicate

Nanotubes suspended in a fluid medium have been investigated by the electrooptic method. This method is based on measuring the relative changes in the intensity of light transmitted through a suspension of nanotubes with application of an external electric field. The electrooptic effect (difference in these changes for transmitted light plane-polarized along the external field and perpendicularly to it) is analyzed. For aqueous suspensions of Mg₃Si₂O₅(OH)₄ nanotubes, the field and relaxation dependences of this effect are investigated. An analysis of the results obtained suggests that nanotubes, even when their concentration in water is low, form strong stable aggregates, which, however, can be elongated and enlarged under long-term action of strong rf fields.