Semi‐interpenetrating polymer networks based on polyurethane and polyvinylpyrrolidone. II. Dielectric relaxation and thermal behaviour

Semi‐interpenetrating polymer networks (semi‐IPNs) based on crosslinked polyurethane (PU) and linear polyvinylpyrrolidone (PVP) were synthezised, and their thermal and dynamic mechanical properties and dielectric relaxation behavior were studied to provide insight into their structure, especially according to their composition. The differential scanning calorimetry results showed the glass transitions of the pure components: one glass‐transition temperature (T_g) for PU and two transitions for PVP. Such glass transitions were also present in the semi‐IPNs, whatever their composition. The viscoelastic properties of the semi‐IPNs reflected their thermal behavior; it was shown that the semi‐IPNs presented three distinct dynamic mechanical relaxations related to these three T_g values. Although the temperature position of the PU maximum tan δ of the α‐relaxation was invariable, on the contrary the situation for the two maxima observed for PVP was more complex. Only the maximum of the highest temperature relaxation was shifted to lower temperatures with decreasing PVP content in the semi‐IPNs. In this study, we investigated the molecular mobility of the IPNs by means of dielectric relaxation spectroscopy; six relaxation processes were observed and indexed according the increase in the temperature range: the secondary β‐relaxations related to PU and PVP chains, an α‐relaxation due to the glass–rubber transition of the PU component, two α‐relaxations associated to the glass–rubber transitions of the PVP material, and an ionic conductivity relaxation due to the space charge polarization of PU. The temperature position of the α‐relaxation of PU was invariable in semi‐IPNs, as observed dynamic mechanical analysis measurements. However, the upper α‐relaxation process of PVP shifted to higher temperatures with increasing PVP content in the semi‐IPNs. We concluded that the investigated semi‐IPNs were two‐phase systems with incomplete phase separation and that the content of PVP in the IPNs governed the structure and corresponding properties of such systems through physical interactions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1191–1201, 2003     

Energy-Saving Technology of Assorted Glassware Decoration by Plasma Spraying

Glass and Ceramics - An energy-saving technology for decorating assorted glassware by plasma spraying of colored assorted and container glasses was developed. The optimal spraying parameters for...     

Influence of residual solvent on physical and chemical properties of amorphous glassy polymer films

One of the most important areas of current research is the study of the influence of the prehistory of samples of amorphous glassy polymers on their physical and chemical properties. The study of structural changes by high temperature IR spectroscopy compared with of quantum chemical calculations allows for an understanding of the mechanism and nature of such processes. The changes in the structure of the polymer chain depending on the type of solvent used in the formation of the films are demonstrated using the examples of several different classes of polymers. In turn, the impact of such changes in the structure on the physical and chemical properties of the polymer films is demonstrated. © 2013 Society of Chemical Industry     

Nanofluids for energetics: effect of stabilization on the critical heat flux at boiling

Investigation of aqueous nanofluids synthesized for the first time based on the natural alumosilicate attapulgite showed their high efficiency as heat-transfer agents and the ability to provide a more than twofold increase of the critical heat flux (CHF) as compared to that of the base liquid (pure water). It is shown that insignificant additives of sodium pyrophosphate, which produce disaggregation of nanoparticles and stabilization of attapulgite-containing nanofluids, significantly improve their thermal properties and heatexchange parameters. Several mechanisms are proposed for interpretation of the observed CHF growth. It is established that the use of attapulgite nanofluids not only allows higher CHF to be reached as compared to that of pure water, but also eliminates sudden onset of the boiling crisis.     

Interatomic interaction and vacancy mobility in FCC metals

A simple set of equations is derived to determine the Morse interatomic interaction potential parameters without any assumptions. These parameters are calculated for a model fcc crystal represented as 30 configuration spheres made of 1060 atoms surrounding a central atom. The dependences of these parameters on the number of surrounding atoms are obtained. The found parameters are used to calculate the energies of vacancy migration in 11 fcc metals using the proposed configuration sphere method.     

Assessing the Strategic Efficiency of Aviation Projects

Russian Engineering Research - The strategic efficiency of a project is defined. An approach to assessing the strategic efficiency of projects is outlined. This approach, incorporated in the State...     

Enhanced performance of FeOOH/ZnIn2S4/Au nanosheet arrays for visible light water splitting

Journal of Materials Science: Materials in Electronics - Carrier separation, charge transport, and visible light absorption are the main factors affecting the solar water splitting performance of a...     

Change in the nature of hydrodynamic cavitation in nonuniform magnetic fields

It is known that in nonuniform magnetic fields the precavitation properties of aqueous media change, leading to an increase in the irreversible physicochemical changes.Notation l length of zone II - D and d diameters of tubes I, III, and II - p_I, p_II, p_III pressures in regions I, II, and III - p_cr critical pressure at which cavitation occurs - p_cr and p _cr ⁰ critical pressures in the magnetic field and when there is no magnetic field - [V_I, V_II, V_III] velocities of the liquid in regions I, II, and III - V_II, lim velocity of the liquid at which breakdown of the hydrated layer occurs for a certain value of the induction - V_cr and V _cr ⁰ critical velocities at which cavitation occurs in the magnetic field and when there is no magnetic field - p_a atmospheric pressure - p_sv saturation-vapor pressure at the given temperature - density of the liquid - kinematic viscosity - Re Reynolds number - Re_cr critical Reynolds number - c_gf and c_gd concentrations of free and dissolved gases in the magnetic field and when there is no magnetic field - c_gf and c_gd, and c _gf ⁰ and c _gd ⁰ concentrations of free and dissolved gases in the magnetic field and when there is no magnetic field - _sc space-charge density - electrical conductivity in the volume of the liquid - _b electrical conductivity in the boundary layer - _l , _g, _d dielectric constants of the liquid in the volume, of the gas in the bubbles, and of the diffusion layer - j, j_b, j_i, and j_T current density of the general, boundary layer, induced and current flow - f_MHD and f_EHD volume forces of magnetohydrodynamic and electrodynamic nature (per unit volume) - p_MHD pressure in the liquid due to the action of the magnetohydrodynamic forces - ₀ limiting shear stress in the liquid - B magnetic induction - E electric field strength in the volume of the liquid Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 5, pp. 842–850, November, 1978.     

Improving the power efficiency of air refrigeration turbomachines

One way of improving the power efficiency of air refrigerating turbo-machines (RTM) is to combine low temperature production with mechanical power generation, sea water desalination or in the processing of some technological products. A study has shown that refrigeration and electrical power generation via the combined application of RTM and gas turbine units will decrease refrigeration costs by 15–20%. In the case of regenerative systems utilizing waste heat from the RTM for sea water demineralization, the cost of low temperature production can be reduced by 15–20%. In addition, a high quality distillate is produced at the rate of 10–15 kg for every 1000 kJ of refrigeration.     

Selection of rational methods of calculating the thermodynamic properties of compressed gases

Translated from Khimicheskoe i Neftyanoe Machinostroenie, No. 5, pp. 26–29, May, 1992.