Таємниця одного адміністратора

Провінційний чиновник, особливо дореформених часів, – і досі рідкісний гість на сторінках вітчизняних наукових монографій, дисертаційних досліджень, ба, навіть, статей у спеціалізованих періодичних виданнях. Поясненням цього феномену є, мабуть, сформована ще класичною російською літературою і діяча-ми доби Великих Реформ слава більшості миколаївських чиновників чи то як «сірості», посередності (стор. 73), чи то як хабарників і крадіїв [1]. З іншого боку, тривалій відразі до студій з адміністративної історії прислужилася логіка т.зв. «національного наративу», за якою місцевий представник імперської адміністра-ції видавався своєрідним «чужинцем» – колоніалістом чи колабораціоністом. Втім, останні десять років досі так само національно орієнтовані англо- і російськомовна історіографії демонструють тенденцію до «імперського пово-роту» («imperial turn»), зокрема, актуалізуючи і переосмислюючи проблематику адміністрування Російської імперії [2]. Вкупі зі зростаючою від часів Великих Реформ кількістю поодиноких праць із історії місцевого управління [3], зокре-ма, і біографічного спрямування [4], це дозволяє очікувати і вітчизняного рене-сансу студій у царині адміністративної історії

The Role of Structure in Polymer Rheology: Review

The review is devoted to the analysis of the current state of understanding relationships among the deformation-induced structure transformations, observed rheological properties, and the occurrence of non-linear effects for polymer liquids (melts, solutions, and composites). Three levels of non-linearity are the base for consideration. The first one concerns changes in the relaxation spectra of viscoelastic liquids, which are responsible for weak non-linear phenomena. The second one refers to the strong non-linearity corresponding to such changes in the structure of a medium that leads to the emergence of a new relaxation state of a matter. Finally, the third one describes the deformation-induced changes in the phase state and/or the occurring of bifurcations and instability in flow and reflects the thermodynamic non-linear behavior. From a structure point of view, a common cause of the non-linear effects is the orientation of macromolecules and changes in intermolecular interaction, while a dominant factor in describing fluid dynamics of polymer liquids is their elasticity. The modern understanding of thixotropic effects, yielding viscoplastic materials, deformation-induced phase transition, and the experimental observations, demonstrating direct correlations between the structure and rheology of polymer liquids, are the main objects for discussion. All these topics are reviewed and discussed mainly on the basis of the latest five-year publications

Flow behaviour of highly concentrated emulsions of supersaturated aqueous solution in oil

A set of highly concentrated water-in-oil emulsions with supersaturated dispersed phase were investigated in this work to verify and/or develop the models that have been presented both in the literature and in this work. The material used to form emulsions consisted of supersaturated oxidiser solution, hydrocarbon oil and PIBSA-based surfactants. The interfacial characteristics for different surfactant types were first examined. Then, the rheology of samples was studied, and different scaling methods and fitting of experimental data were studied. On the basis of flow curve measurements and observed τ\emphv∼γ˙1/2τ\emphv∼γ˙1/2 scaling, a modified version of Windhab model was suggested which showed excellent fitting of experimental results. The linear dependences of τy0/σ versus 1/d32 for studied emulsions showed non-zero intercept which implies a non-linear dependence (resulting from interdroplet interaction) to fulfil the zero-intercept requirement. It was established that the zero intercept condition was fulfilled in the τy0∼σ/d232τy0∼σ/d322 scaling, although the experimental results for different surfactants were not superimposed

Rheology of Gels and Yielding Liquids

In this review, today’s state of the art in the rheology of gels and transition through the yield stress of yielding liquids is discussed. Gels are understood as soft viscoelastic multicomponent solids that are in the incomplete phase separation state, which, under the action of external mechanical forces, do not transit into a fluid state but rupture like any solid material. Gels can “melt” (again, like any solids) due to a change in temperature or variation in the environment. In contrast to this type of rheology, yielding liquids (sometimes not rigorously referred to as “gels”, especially in relation to colloids) can exist in a solid-like (gel-like) state and become fluid above some defined stress and time conditions (yield stress). At low stresses, their behavior is quite similar to that of permanent solid gels, including the frequency-independent storage modulus. The gel-to-sol transition considered in colloid chemistry is treated as a case of yielding. However, in many cases, the yield stress cannot be assumed to be a physical parameter since the solid-to-liquid transition happens in time and is associated with thixotropic effects. In this review, special attention is paid to various time effects. It is also stressed that plasticity is not equivalent to flow since (irreversible) plastic deformations are determined by stress but do not continue over time. We also discuss some typical errors, difficulties, and wrong interpretations of experimental data in studies of yielding liquids

Scaling in pipeline flow of Kaolin suspensions

The dimensionless analysis is applied to pipeline transportation of Kaolin suspensions. Experimental data were obtained for flow through pipes of different diameters. The rheological properties of materials under study were characterized by the Hershel–Bulkley equation. The method of constructing the modified Reynolds number, Rem for visco-plastic materials was discussed. It was shown that in a wide range of the Reynolds number (up to five decimal orders) the experimental data is well fitted by the standard f = 16/Rem dependence up to the laminar-to-turbulent transition point. The transition point (critical Reynolds number, View the MathML source) is a linear function of the pipe diameter. At View the MathML source, the f(Rem) becomes dependent upon pipe diameter. Using the View the MathML source value as a scaling factor, it is possible to construct a universal dependence of View the MathML source versus View the MathML source, which is valid for the entire range of velocities and pipe diameters under study. In the laminar-to-turbulent transition zone this dependence approaches the asymptote View the MathML source and the pressure gradient becomes a quadratic function of average velocity

The Elasticity of Polymer Melts and Solutions in Shear and Extension Flows

This review is devoted to understanding the role of elasticity in the main flow modes of polymeric viscoelastic liquids—shearing and extension. The flow through short capillaries is the central topic for discussing the input of elasticity to the effects, which are especially interesting for shear. An analysis of the experimental data made it possible to show that the energy losses in such flows are determined by the Deborah and Weissenberg numbers. These criteria are responsible for abnormally high entrance effects, as well as for mechanical losses in short capillaries. In addition, the Weissenberg number determines the threshold of the flow instability due to the liquid-to-solid transition. In extension, this criterion shows whether deformation takes place as flow or as elastic strain. However, the stability of a free jet in extension depends not only on the viscoelastic properties of a polymeric substance but also on the driving forces: gravity, surface tension, etc. An analysis of the influence of different force combinations on the shape of the stretched jet is presented. The concept of the role of elasticity in the deformation of polymeric liquids is crucial for any kind of polymer processing

Size dependence of the elastic modulus of thin polymer fibers – modeling

The problem of the size dependence of physical properties is one of the most intriguing when we transit to the nano-level. Experiments have shown that this effect is characteristic of the elastic modulus of many polymeric nanofibers obtained by electrospinning. Existing explanations of this effect did not offer a general understanding of the physical nature of this phenomenon. In this study, we propose a universal model of this phenomenon. We consider the structure of fibers within the framework of the core-shell model, in which the shell is approximated by a thin elastic surface. The analysis of deformation is based on the fundamental laws of the mechanics of deformation of twisted thin shells and, unlike the theories proposed earlier, does not require any additional artificial arguments. This approach made it possible to obtain a simple analytical expression for the size dependence of the elastic modulus, which represents it as the sum of the bulk modulus of the core and two additional moduli proportional to D–1 and D–3, respectively. The resulting model corresponds to all available (from published sources) experimental data, related to polymer of very different chemical structure, and therefore can be considered as universal

Evolution of rheological properties of highly concentrated emulsions with aging — Emulsion-to-suspension transition

The effect of aging on the rheological properties and physical structure of highly concentrated water-in-oil emulsions with dispersed phase of 82–90v%82–90v% is the subject of this study. It was proven by various experimental techniques that aging leads to the emulsion-to-suspension transition. Significant shift of rheological properties to the solid-like behavior is the result of the emulsionsaging, which shows itself as an increase of the storage modules with time as well as Newtonian viscositymeasured in the upward sweeping shear rate mode. Comparison of flow curves measured in the upward and downward sweeping shear rate modes shows that the rheopectic effect at low stresses is observed for both fresh and aged emulsions.Viscosity measurements in the downward mode demonstrate transition to the elastic-like behavior at low stresses with appearance of strongly pronounced yield stress. Dependencies of the characteristic rheological parameters on aging have been investigated by using different analytical methods such as optical microscope studies, differential scanning calorimetry measurements, and x-ray diffraction. All these methods showed that aging is associated with the process of slow crystallization of the dispersed droplets that comprise of overcooled highly concentrated aqueous solution, which can be considered as the main mechanism for the evolution of the emulsion's rheological properties. In this sense, the observed emulsion-to-suspension transition is the consequence of the phase transition. The kinetics of the transition process is described by the Johnson-Mehl-Avrami-Kolmogorov equation and correlates with the evolution of the rheological properties of the dispersion.African Explosives Limite

A Novel Technique for Fiber Formation: Mechanotropic Spinning—Principle and Realization

We present basic experimental data and the theoretical background of a novel technique for fiber spinning from polymer solutions. The principal feature of the advanced process is realization of phase separation with detachment of a solvent, accompanied by the orientation of macromolecules, under the action of high extension rates. This is similar in some respects to dry spinning, though the driving force is not diffusion with subsequent evaporation of a solvent but redistribution of polymer-solvent interactions in favor of polymer-polymer and solvent-solvent ones governed by mechanical stresses. A promise of this approach has been demonstrated by experiments performed with polyacrylonitrile solutions in different solvents and solutions of the rigid-chain aromatic polyamide. We examined mechanotropic fiber spinning in model experiments with stretching jets from a drop of polymer solution in different conditions, and then demonstrated the possibility of realizing this process in the stable long-term continuous mode. During extension, phase separation happens throughout the whole section of a jet, as was confirmed by visual observation. Then a solvent diffuses on a jet surface, forming a liquid shell on the oriented fiber. Instability of this cover due to surface tension leads either to formation of separate solvent drops “seating” on the fiber or to the flow of a solvent down to the Taylor cone. The separate liquid droplets can be easily taken off a fiber. The physics underlying this process is related to the analysis of the influence of macromolecule coil-to-stretched chain transition on the intermolecular interaction

Rheological Properties of Fish Gelatin Modified with Sodium Alginate

Polyelectrolyte complexes of sodium alginate and gelatin obtained from cold-blooded fish were studied for potential application as structure-forming agents in food hydrogels. The mass ratio of sodium alginate to gelatin plays a decisive role in the sol-gel transition and rheological behavior of the complexes. Differences in the sol-gel transition temperature were observed upon heating and cooling, as is typical for such materials. We investigated the characteristics of this transition by measuring the isothermal changes in the elastic modulus over time at a constant frequency and the transition temperature at a range of frequencies. The kinetic nature of this transition depends on the composition of the complexes. A characteristic alginate-gelatin mass ratio is the ratio at which maximum transition temperature as well as elastic modulus and viscosity (rheological parameters) values are obtained; the characteristic mass ratio for these complexes was found to be 0.06. Calculation of the ionic group ratios in the biopolymers that form complexes and comparison of these data with the turbidimetric titration results clarified the origin of these maxima. Measuring the viscoelastic properties and the creep-elastic recoil of the samples allowed us to characterize these materials as viscoelastic media with a viscosity in the order of 103–104 Pa·s and an elastic modulus in the order of 102–103 Pa. These values drastically decrease at a certain stress threshold, which can be treated as the gel strength limit. Therefore, the observed rheological behavior of gels formed by fish gelatin modified with sodium alginate characterizes them as typical viscoelastic soft matter