Mixed micelles based on cationic and anionic amphiphilic diblock copolymers containing identical hydrophobic blocks

Through the use of the methods of turbidimetry, UV spectrophotometry, fluorescence spectroscopy, dynamic light scattering, and ultracentrifugation, micelle formation is studied for cationic (polysty-rene-poly-N-ethyl-4-vinylpyridium bromide) and anionic (polystyrene-sodium polyacrylate) diblock copolymers containing identical polystyrene blocks in dilute aqueous saline solutions. Mixing of aqueous dispersions of individual micelles is accompanied by the formation of only insoluble products, which likely are intermicellar interpolyelectrolyte complexes. At the same time, mixing of diblock copolymers in a nonselective solvent and its subsequent gradient replacement with water during suppressed interpolyelectrolyte interactions yields mixed diblock copolymer micelles, which are found to be dispersionally stable in an excess of charged units of any polymer component. The micelles are composed of an insoluble polystyrene core and a mixed interpolyelectrolyte corona, and their hydrodynamic characteristics are controlled by the ratio of charged units in the mixed diblock copolymers. The mixed micelles are found to be able to interact with the macromolecules of a homopolyelectrolyte, sodium poly(styrene sulfonate), in aqueous solutions and form ternary complexes. In this case, depending on the composition of the mixed micelles, ternary complexes can be dispersionally stable or can aggregate and precipitate.     

Experimental Study of the Polydispersity of Aqueous Colloid of Palygorskite and Suspensions of Escherichia Coli and Pseudomonas Fluorescens by an Electrooptical Method

The results of experimental study on the polydispersity of an aqueous colloid of palygorskite and aqueous suspensions of Escherichia coli (E. coli) and Pseudomonas fluorescens(Ps. fluorescens) are reported. The study is based on the use of a new method; i.e., on the investigation of an electrooptical effect appearing when a weak sinusoidal electric field with sinusoidal amplitude modulation is applied on the system. This method was developed for studying systems in which only slight particle orientation is possible under action of an external electric field. Disperse systems with a high conductivity, including cell suspensions and other biocolloids, colloids containing small particles, as well as solutions of macromolecules and polyelectrolytes, are among such systems. The experimental setup developed in this work is described. The results obtained are compared with data of microscopic measurements and the results of the study of polydispersity in strong fields based on the investigation of the relaxation of electrooptical effect.     

Electro-optical study of the correlation between dimensions and polarizability of particles in colloid systems

The applicability of methods of molecular electro-optics for the study of colloid systems is analyzed. It is shown that the basic formulas of molecular electro-optics can be applied for the calculation of electrical and geometric characteristics of particles of colloid size. The basic integral equations describing electro-optical effects in colloid systems are presented to find distributions of particles over their size and polarizability anisotropy. The accuracy of their solutions is evaluated by mathematical simulation. Studying the dichroism induced by an external electric field in aqueous colloids of anisylidenbenzidine and graphite, the polarizability and size distribution functions are found for particles with an “optical weight.” From the resulting distribution functions, the statistical dependences of the polarizability anisotropy of those particles on their size are found and analyzed.     

Lasers based on vapors of complex organic compounds

The properties of the emission of lasers based on complex organic compounds, in the quasistationary lasing regime, are theoretically investigated with allowance for the induced losses in the spectral lasing region in the system of triplet and excited singlet states of the molecules. The results of the calculations are compared with the experimental data for lasers using POPOP and TOPOT vapors. The thermal endurance of these compounds at T < 600OlaggyK is investigated, the constants of the singlet-triplet conversion and the cross sections for the absorption of the excited singlet molecules TOPOT in the lasing band are determined, and the effectiveness of stabilizing the POPOP and TOPOT vapors by a buffer gas is estimated.The paper contains results of calculations and experiments included in the candidate's dissertation of K. K. Trusov, Investigation of lasers based on vapors of complex organic compounds, Moscow, Physics Institute of the Academy of Sciences, 1978).Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Akademii Nauk SSSR, Vol. 125, pp. 20–45, 1980.     

Comparative analysis of some formulations of the stability problem

Various formulations of the problem of stability of uniaxial tension of a band under superplastic strains are analyzed. A more general formulation (as compared to those available) is proposed; criteria of stability are obtained. Various methods of describing the behavior of materials in the superplasticity regime are considered. __________ Translated from PrikladnayaMekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 110–117, January–February, 2009.     

Specific features of the electrooptical effect and light scattering of water dispersed system of carbon nanotubes

Results of an electrooptical study of a water solution of carbon nanotubes obtained using the catalytic method are presented. It is shown that nanotubes, which anisotropically absorb light, are oriented in an electric field and create a pronounced linear electric dichroism due to light absorption, rather than light scattering (as in the case of colloids with particles with sizes close to that of nanotubes). An analysis of the relaxation dependences of the electric dichroism shows that nanotubes deform, which are oriented in the electric field; in this case, the deformation sublinearly depends on the field amplitude and reaches a limiting value. The relaxation dependence of the field-induced dichroism agrees with the autocorrelation function of depolarized light scattered perpendicular to the incident light flux.     

Theoretical upper bound on the mass of the LSP in the MNSSM

We study the neutralino sector of the Minimal Non-minimal Supersymmetric Standard Model (MNSSM) where the μ problem of the Minimal Supersymmetric Standard Model (MSSM) is solved without accompanying problems related with the appearance of domain walls. In the MNSSM as in the MSSM the lightest neutralino can be the absolutely stable lightest supersymmetric particle (LSP) providing a good candidate for the cold dark matter component of the Universe. In contrast with the MSSM the allowed range of the mass of the lightest neutralino in the MNSSM is limited. We establish the theoretical upper bound on the lightest neutralino mass in the framework of this model and obtain an approximate solution for this mass.     

Formation of submicron-sized SrFe12−xAlxO19 with very high coercivity

Submicron-sized SrFe_12−xAl_xO₁₉ (x=1.3) was formed in glass-ceramic matrix using controlled thermocrystallization of the SrO–Fe₂O₃–Al₂O₃–B₂O₃ glass and the hexaferrite powder was obtained by removing the matrix phases. The samples were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray (EDX) analysis and magnetization measurements. The glass-ceramic material exhibits very high coercivity value up to 10.18 kOe which approaches a theoretically estimated maximum value for the compound. The hexaferrite powder consists of well faceted single crystals, which adopt the shape of a truncated hexagonal bipyramid. The powder saturation magnetization value is close to the theoretically estimated one for bulk material. Crystal structure of the powder was refined by Rietveld method and distribution of Al atoms on Fe sites was determined. Al atoms occupy 41% of 2a sites, 14% of 12k sites and 5% of 4e(1/2) sites, while 4f sites are not affected.