V.V. Shilov

Molecular mobility and protonic conductivity in polymers: hydrogels and ionomers

Abstract Dielectric relaxation spectroscopy (DRS) in wide ranges of frequency (10 −2 –10 10 Hz) and temperature (170–350 K) and thermally stimulated depolarization currents (TSDC) techniques (77–300 K) were employed to study protonic conductivity and molecular mobility in poly(ethylene oxide) (PEO) hydrogels and in novel segmented polyurethane ionomers. High protonic DC conductivity values are obtained with both systems. In the hydrogels the results are discussed in terms of polymer–water interactions, and of temperature- and water-induced effects. In the ionomers additional information on microphase separation and ionic aggregation obtained by means of DSC, WAXS, SAXS and DMTA measurements provides a basis for discussing structure–property relationships in this class of materials. Proton conductivity in both systems is governed by the motion of the polymeric chains. In the ionomers DC conductivity increases with decreasing hard segment content, suggesting that proton motion occurs through the soft segments phase.

Phase separation in blends of oligo (caprolactone glycol)-based polyurethane with poly(vinyl chloride)

The structure of o!igo (caprolactone glycol)-based polyurethane-poly(vinyl chloride) (PVC) blends obtained from tetrahydrofuran solution was studied by X-ray diffraction and electron microscopy. The system is characterized by a oornp!ex phase diagram with two types of equilibria: (1) crystal-liquid equilibrium in the region of blend compositions up to 40 wt% PVC; (2) liquid-liquid equilibrium in the region of man compositions. The crystallization kinetics of oligo(caprolactone) polyurethane blocks from an initially compatible amorphous blend was investigated. Small-angle X-ray cattering (SAXS) studies provide evidence that the amorphous component (PVC) is incorporated in the interlamellar crystalline regions of the compositions. The amorphous blends are characterized by the presence of modulated structures at two scale levels, this being explained as e result of the process in which the bulk samples were obtained from a three-component polymer-polymer-solvent system.

X-ray diffraction studies on liquid crystalline order in vinyl polymers with mesogenic side-groups

Abstract X-ray studies on some vinyl polymers with azobenzene sidegroups were performed. A model of layered structure rearrangement resulting from the substitution of the methacrylate main chain for the acrylate is proposed. It has been shown that the perfection of a layered structure is reduced with shortening of the flexible tail of the mesogenic group. Improvement of LC order with increase of temperature was revealed.

Morphology, dielectric relaxation and conductivity of the novel polyurethanes with acid and ionic groups in the polyether segments

Abstract The thermal transitions, microphase structure, local segmental and conductivity relaxation of the novel polyurethanes (PUs) based on the poly(tetramethylene glycol) as soft segments (SSs) and 4,4′-diphenylmethane diisocyanate-1,4-butane diol sequences of various length as hard segments (HSs) containing acid or ionic groups in SSs are studied by calorimetry, X-ray scattering and dielectric relaxation spectroscopy. The techniques used include differential scanning calorimetry, 173–473 K, wide-angle X-ray scattering, (WAXS) small-angle X-ray scattering (SAXS), broad band dielectric relaxation spectroscopy (DRS), 10−2–106 Hz, and thermally stimulated depolarization currents (TSDC) techniques, 100–300 K. The peculiarities of microphase-separated structure (MSS) of the PUs such as composition of the microphases, periodicity of non-ionic PU MSS (about 17 nm), size of ionic aggregates in the ionomer (about 7 nm) and their distribution in the SS matrix were determined. The features of α-relaxation, conductivity relaxation and dc conductivity of the proton-conducting PU with acid groups and ion-conducting PU with ionic ones are found and discussed in connection with MSS of the PUs. The level of protonic dc conductivity increases with temperature up to 10−5 S/m (323 K), whereas the ionic PU exhibits by about two decades lower conductivities, evidently due to ionic aggregation. Accordingly for the latter, apparent activation energy of the conductivity relaxation is considerably more than for the former.

Recent Successes in Structural Studies of Thermotropic Liquid Crystalline Polymers

Abstract Liquid crystals are widespread in nature and are synthesized in large amounts for various practical applications which are associated with the unique properties inherent in these compounds. These include the following: practically instant change of the macroproperties (color, light transmission, etc.) under the action of small gradients of stress, electric, magnetic, and thermal fields, and also with a change of chemical composition of the environment [1-7]. A suitable form of visual response to external actions, high sensitivity, and a wide range of “memory” times ensure practically unlimited fields of application for liquid crystal (LC) compounds. There are optical memory; light filters; fast-response optoelectronic gates; polarizers (nematic and smectic LC); temperature, stress, pressure, and chemical composition indicators; TV receivers; displays, and light panels (cholesteric and smectic LC). Due to such diverse fields of application, LC systems should meet a number of design requirements. F...

Structure and molecular mobility studies in novel polyurethane ionomers based on poly(ethylene oxide)

Abstract Novel polyurethane ionomers based on poly(ethylene oxide) with nonionic hard segments of varying length and flexible segments containing alkali ions (or protons) have been prepared and their structure–property relationships have been investigated. Differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) were employed for structural investigation, whereas molecular mobility and ionic conductivity were studied by means of thermally stimulated depolarization currents (TSDC) techniques and of broadband (10 −2 –10 9 Hz) dielectric relaxation spectroscopy (DRS). The ionomers are characterized by the coexistence of the segment microphase separation and the ionic group segregation morphologies. Crystallization is observed at low hard segment contents (melting at about 305 K), the tendency for crystallization decreasing upon hard segment extension and decreasing upon neutralization. Values of ionic conductivity are in the range of 10 −4 S/m at 323 K, the conductivity in the amorphous polyurethanes being governed by the motion of the polymeric chains.

Microheterogeneous structure of liquid crystalline polymers

Abstract Liquid crystalline polymers with phenyl benzoate side groups with various lengths of flexible chain-end were synthesized. Small-angle X-ray scattering studies were carried out. Layer structures in the liquid crystalline polymers were characterized and the microheterogeneous structure was investigated. It was concluded that the microstructure is dependent on the length of the flexible mesogenic chain-end.

Critical phenomena in a polymer-solvent system: slow neutron transmission technique

Abstract The slow neutron transmission technique was used to study the shape of the coexistence curves for polystyrene-deuterocyclohexane solution in the fluctuation region of the critical mixing point. Critical indices and amplitudes of the scaled equation for the coexistence curve were determined. From the data obtained, one can conclude that the system belongs to the same universality class as the Ising model. It is shown that the use of different order parameters did not change the numerical values of critical indices of the coexistence curve and caused only the renormalization of amplitudes. Near the critical mixing point the gravity effect was observed, its temperature range being in agreement with theoretical predictions.

Organic-Inorganic Insulating Coatings Based on Sol-Gel Technology

The approach for improving bending strength of temperature-resistant flexible ceramic electric insulating coatings prepared by sol-gel processing is considered. Starting suspensions, based on both tetraethoxysilane (TEOS)-derived modified sols and highly dispersed fillers such as Cr2O3, are used to deposit the coatings on metals and alloys. Some polymers and organic substances are tested as additives for improving flexibility of the ceramic coatings. The results of study of both bending strength and electrical strength of flexible hybrid organic-inorganic insulation formed on a nichrome wire are discussed. The data obtained on the chemical and phase structure of the coatings, which have been heat treated at temperatures from 95 to 1100°C, using DSC as well as X-ray scattering techniques are presented.

Structure and electrical conductivity in novel polyurethane ionomers

Novel polyurethane (PU) ionomers based on poly(teramethylene oxide) (PTMO) or poly(ethylene oxide) (PEO), with nonionic hard segments of varying length and flexible segments containing sodium ions (Na + ), have been prepared and their structure-property relationships have been investigated. The structure and the morphology were studied by means of differential scanning calorimetry (DSC), infrared (IR) spectroscopy and small-angle X-ray scattering (SAXS). Ionic conductivity was studied by means of broadband dielectric relaxation spectroscopy (DRS, 10 -2 -10 9 Hz). PTMO-based ionomers are characterized by the coexistence of segment microphase separation and ionic group segregation morphologies. In the PEO-based ionomers, crystallization is observed at low hard segment content, with a tendency for crystallization to decrease upon hard segment extension. Values of ionic conductivity are in the range 10 -7 Sm -1 to 10 -4 Sm -1 at 323 K for PU ionomers based on PTMO and PEO, respectively.