Self-diffusion of molecules in aqueous solutions of tetramethylurea

Solutions of tetramethylurea (I) in light and heavy water were studied by the proton spin echo method over a wide concentration range at different temperatures. The energies of self-diffusion activation for species in these systems were calculated. In the both systems, the lowest coefficient of self-diffusion and the highest energy of activation for all the temperatures studied (288 to 313 K) were found for its ∼20 mol % solution, which corresponds to a congruently melting compound in the solid phase and to maximum sound viscosity, density, and speed in aqueous solutions of tetramethylurea. The low-concentration range of compound I (from 1.2 to 5 mol %) proved to be featureless

A viscometric study of the liquid crystalline phase of alkyloxybenzoic acids

The viscosities of three benzoic acid derivatives (p-n-heptyloxy-, p-n-decyloxy-, and p-n-dodecyloxy-) were measured on a unique viscometer of the class of CS-rheometer-viscometers with controlled shear stress over the whole temperature range of the liquid crystalline state. Shear rates were calculated and flow and viscosity curves constructed from the experimental shear stress values taking into account the Rabinovich-Moony correction. The smectic and nematic phases were characterized by non-Newton and Newton viscosities, respectively, in all the samples studied. The activation parameters of viscous flow were calculated for Newton viscosity. The results are discussed in terms of intermolecular interactions and structural peculiarities of liquid crystalline phases. © 2009 Pleiades Publishing, Ltd

Specifics of the physicochemical properties of tetramethylurea

The rotational and translational mobility of tetramethylurea molecules over the temperature range 15-60°C was studied using the NMR relaxation and proton spin-echo methods. The activation energies for these motions were calculated. The density, viscosity, isothermal compressibility, and cubic expansivity were determined. A thermogravimetric analysis of the substance was performed. The physicochemical properties of tetramethylurea were compared to those of urea, its other methyl-substituted derivatives, and dimethylformamide. Copyright © 2005 by Pleiades Publishing, Inc

Rheology of liquid crystalline phases of alkyloxybenzylidene toluidines

A unique viscometer of the CS rheometer viscometer class designed at the Kazan State University of Technology is used to measure viscosities of two p-n-alkyloxybenzylidene-p-toluidines in the entire temperature range of the liquid crystalline state and transition into an isotropic liquid. The measured shear stresses and flow rates are used to calculate shear rates and plot flow and viscosity curves. The liquid crystalline phase and isotropic liquid are demonstrated to possess Newtonian viscosity, whose viscous flow activation parameters are calculated in the temperature range under study. The results are discussed from the standpoint of intermolecular interactions and structural details of the liquid crystalline phase. © 2010 Pleiades Publishing, Ltd

Dielectric spectroscopy of amino alcohols at low temperatures

© 2016 Pleiades Publishing, Ltd. The dielectric properties of three vicinal amino alcohols are studied at temperatures in the range of -140-70°C and the frequency interval of 0.1 Hz to 1 MHz. The temperature dependences of the observed relaxation processes indicate both glass transition and melting processes. The relatively high conductivity of the samples was considered from the viewpoint of proton conductivity through a network of hydrogen bonds of amino alcohol molecules