A Novel Approach to Design Chitosan-Polyester Materials for Biomedical Applications

A novel approach to design chitosan-polyester materials is reported. The method is based on mechanical activation and effective intermixing of the substrates under high pressure and shear deformation in the course of solid-state reactive blending. The marked departure of this approach from previous practice resides on exploitation of a variety of chemical transformations of the solid polymers that become feasible under conditions of plastic flow. Low temperatures (above Tg but below the melting points of the crystalline polymers) are maintained throughout the process, minimizing mechanical and oxidative degradation of the polymers. Morphology as well as structural, mechanical, and relaxation properties of those prepared blends of chitosan with semicrystalline poly(L,L-lactide) and amorphous poly(D,L-lactide-co-glycolide) has been studied. Grafting of polyester moieties onto chitosan chains was found to occur under employed pressures and shear stresses. The prepared polymer blends have demonstrated an amphiphilic behavior with a propensity to disperse in organic solvents that widens possibilities to transform them into promising materials for various biomedical applications

Influence of oxygen vacancies on magnetic and transport properties of thin Zn

The features of the structural, transport and magnetic properties of thin Zn1-xCoxOy films (x=0-0.45), fabricated on С-sapphire substrates by the pulsed laser deposition method are studied. It is found that the transport and ferromagnetic properties of the wurtzite Zn1-xCoxOy films nonmonotonously depend on Co concentration at room temperature. For the Zn0.87Co0.13Oy film, the strongest ferromagnetic signal is observed that is caused by formation of the greatest number of metallic Co clusters. A further increase of doping impurity concentration in the films leads to the oxidation of metallic Co and formation of the paramagnetic Co3O4 phase, in consequence of which the ferromagnetic signal subsides

Influence of oxygen vacancies on magnetic and transport properties of thin Zn1-xCoxOy films

The features of the structural, transport and magnetic properties of thin Zn1-xCoxOy films (x=0-0.45), fabricated on С-sapphire substrates by the pulsed laser deposition method are studied. It is found that the transport and ferromagnetic properties of the wurtzite Zn1-xCoxOy films nonmonotonously depend on Co concentration at room temperature. For the Zn0.87Co0.13Oy film, the strongest ferromagnetic signal is observed that is caused by formation of the greatest number of metallic Co clusters. A further increase of doping impurity concentration in the films leads to the oxidation of metallic Co and formation of the paramagnetic Co3O4 phase, in consequence of which the ferromagnetic signal subsides

Свойства магнитореологических эластомеров в скрещенных переменном и постоянном магнитных полях

Dynamic properties of magnetorheological elastomers (MREs) with barium ferrite particles in the presence of crossed AC and DC magnetic fields were investigated. Calculations of the magnetic permeability were made based on the fact, that the inductance of the coil changes when the coil is filled with the elastomer. Measurements of inductances of an empty coil and the coil with elastomeric core were carried out. The core was smaller than the space inside the coil, so it was able to move within the coil. The dependencies of real and imaginary parts of magnetic permeability on AC field frequency had resonance peaks at different values of DC magnetic field strength. The sample vibration was considered in frame of the elastic rod oscillations model. The change of dielectric permittivity of the elastomer with conductive particles under magnetic field (so-called magnetodielectric effect) was also investigated. These effects are the examples of transformation of the magnetic field energy into the electrical or mechanical energy of the MREработе были исследованы динамические свойства магнитореологических эластомеров (МРЭ) с частицами феррита бария в скрещенных переменном и постоянном магнитных полях. Маг- нитная проницаемость МРЭ была измерена индуктивным методом. При этом эластомерный сердечник измерительной катушки не полностью заполнял пространство внутри катушки и имел возможность двигаться. На зависимостях действительной и мнимой частей магнитной проницаемости от частоты переменного поля присутствуют резонансные пики. Этот эффект рассматривался в рамках модели продольных колебаний упругого стержня. В работе также представлены результаты измерения диэлектрической проницаемости МРЭ с проводящими частицами в магнитном поле (так называемый магнитодиэлектрический эф- фект

Свойства магнитореологических эластомеров в скрещенных переменном и постоянном магнитных полях

Dynamic properties of magnetorheological elastomers (MREs) with barium ferrite particles in the presence of crossed AC and DC magnetic fields were investigated. Calculations of the magnetic permeability were made based on the fact, that the inductance of the coil changes when the coil is filled with the elastomer. Measurements of inductances of an empty coil and the coil with elastomeric core were carried out. The core was smaller than the space inside the coil, so it was able to move within the coil. The dependencies of real and imaginary parts of magnetic permeability on AC field frequency had resonance peaks at different values of DC magnetic field strength. The sample vibration was considered in frame of the elastic rod oscillations model. The change of dielectric permittivity of the elastomer with conductive particles under magnetic field (so-called magnetodielectric effect) was also investigated. These effects are the examples of transformation of the magnetic field energy into the electrical or mechanical energy of the MREработе были исследованы динамические свойства магнитореологических эластомеров (МРЭ) с частицами феррита бария в скрещенных переменном и постоянном магнитных полях. Маг- нитная проницаемость МРЭ была измерена индуктивным методом. При этом эластомерный сердечник измерительной катушки не полностью заполнял пространство внутри катушки и имел возможность двигаться. На зависимостях действительной и мнимой частей магнитной проницаемости от частоты переменного поля присутствуют резонансные пики. Этот эффект рассматривался в рамках модели продольных колебаний упругого стержня. В работе также представлены результаты измерения диэлектрической проницаемости МРЭ с проводящими частицами в магнитном поле (так называемый магнитодиэлектрический эф- фект

Preparation, phase stability, and magnetization behavior of high entropy hexaferrites

Summary: The polycrystalline SrFe12O19 samples deeply substituted up to at.67% by Al3+, Ga3+, In3+, Co3+, and Cr3+ cations with a high configurational mixing entropy were prepared by solid-phase synthesis. Phase purity and unit cell parameters were obtained from XRD and analyzed versus the average ionic radius of the iron sublattice. The crystallite size varied around ∼4.5 μm. A comprehensive study of the magnetization was realized in various fields and temperatures. The saturation magnetization was calculated using the Law of Approach to Saturation. The accompanying magnetic parameters were determined. The magnetic crystallographic anisotropy coefficient and the anisotropy field were calculated. All investigated magnetization curves turned out to be nonmonotonic. The magnetic ordering and freezing temperatures were extracted from the ZFC and FC curves. The average size of magnetic clusters varied around ∼350 nm. The high values of the configurational mixing entropy and the phenomenon of magnetic dilution were taken into account