Magnetorheological and deformation properties of magnetically controlled elastomers with hard magnetic filler

Viscoelastic and deformational behavior of soft magnetic elastomers with hard magnetic fillers under the influence of a magnetic field is studied by different experimental techniques. The magnetic elastomers used in this work were synthesized on the basis of silicone rubber filled with FeNdB particles and were magnetized in a field of 3 and 15 kOe. We have shown that due to high residual magnetization the materials demonstrate well pronounced non-elastic behavior already in the absence of any external magnetic field. In particular, in contrast to magnetic elastomers based on soft magnetic fillers their elastic modulus is strain-dependent. Under the influence of external magnetic field the storage and loss moduli of magnetic elastomers with hard magnetic filler can both increase and decrease tremendously.     

Electronic structure and absorption spectra of products from single-electron reduction of derivatives of 4,4′-dipyridyl

The Hartree-Fock absolute method has been used in the -electron approximation to investigate the absorption spectra of a number of cation-radical salts of derivatives from 4,4-dipyridyl with the objective of explaining the interrelation between their electronic structure and the nature of the set of these salts with the spectroscopic characteristics. The characteristic absorption spectrum of cation-radicals of 4,4-dipyridyl and its derivatives is formed due to the merging of three absorption bands of different natures, localized on the dipyridyl fragment. In the absorption spectra of products from single-electron reduction of dications of 4,4-dipyridyl a band is observed from charge transfer between the cation-radical and the dication, and also an absorption band of the -dimers being formed as a result of spin-spin interaction of the cation-radicals.Scientific Publications of the "Monocrystal Reagent" Association, Khar'kov, Khar'kov University. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 752–757, November–December, 1987.The authors express their deep gratitude to I. V. Krivoshei for constant interest in the work, attention and support, to A. V. Luzanov and V. É. Umanskii for valuable discussions and making available calculation programs for electronic characteristics of the molecules.     

Novel highly elastic magnetic materials for dampers and seals: Part I. Preparation and characterization of the elastic materials

The new generation of magnetic elastomers represents a new type of composites, consisting of small (mainly nano and micron‐sized) magnetic particles dispersed in a highly elastic polymeric matrix. The combination of polymers with magnetic materials displays novel and often enhanced properties. Highly elastic magnetic composites are quite new and understanding of the behavior of these materials depending on the composition, external conditions, and the synthesis processes is still missing. Thus, the aim of this work is the study of fundamental principles governing the preparation of these materials as well as their structure and elastic properties. Copyright © 2007 John Wiley & Sons, Ltd.     

Formation of Salt Bonds in Polyampholyte Chains

In this paper we study the influence of the formation of intrachain ion pairs (salt bonds) and the distribution of counterions on the behavior of single polyampholyte chains in a dilute solution. It has been shown that neutral polyampholyte chains can undergo jump‐like collapse transition from the swollen state to the globular state with the formation of ion pairs between oppositely charged ions of the chain. A polyampholyte chain with an excess charge shows the behavior of a conventional polyelectrolyte chain and counterions play an important role in the chain behavior. We distinguish three possible states of counterions: free counterions inside and outside the macromolecule, and a bound state of counterions forming ion pairs with the corresponding ions of the polymer chain. We found a non‐monotonous behavior of the chain upon increasing the excess charge on the chain: the chain swells from a compact state to elongated conformation and shrinks again to the compact state when the excess charge of the chain is increased.     

A three‐state model for counterions in a dilute solution of weakly charged polyelectrolytes

In this paper we consider the influence of counterion distribution on the behavior of polyelectrolyte systems. We propose the unified model to describe and to compare the swelling and collapse properties of single polyelectrolyte chains in dilute solutions, microgel particles of various molecular masses, and (as a limiting case) macroscopic gels. A novel feature of the new approach is that we distinguish three possible states of counterions: free counterions inside and outside the polymer macromolecule and a bound state of counterions forming ion pairs with corresponding ions of polymer chains. The latter possibility becomes progressively important when macromolecules or gels shrink. In this case the formation of a supercollapsed state is possible, when all couterions are trapped and form ion pairs. On the other hand, the fact that counterions can float in the outer solution affects essentially the conformation of polyelectrolyte chains in dilute solutions of good quality where practically all counter ions can escape the space inside polymer coils and the repulsion between uncompensated charges plays an important role in the chain behavior.