Papers by Alexander Malkin
Kolloid-Zeitschrift und Zeitschrift für Polymere, 1963
Polymers, 2022
The review is devoted to the analysis of the current state of understanding relationships among t... more 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 interactio...
Polymers, 2021
Powder injection molding (PIM) is one of the modern and prospective technologies in processing di... more Powder injection molding (PIM) is one of the modern and prospective technologies in processing different materials. We proposed to use bimodal compositions of particles for increasing their content in the final products. A set of model suspension of Al with low-molecular-weight poly (ethylene glycol) as a binder based on theoretical arguments concerning the filling capacity of bimodal suspensions was prepared. Studying the rheological properties of these compositions showed that they demonstrate elasto-viscous behavior with significant plasticity that is favorable for the technological process. Using compositions with bimodal distributions allows for increasing the content of the solid phase up to 75 vol. % for PIM technology, which is significantly higher than the standard practical limit. This rheological approach developed for model formulations was applied to processing compositions containing aluminum oxide as typical ceramics and polyolefines as a binder widely used in technol...
Applied Rheology, 2015
Different rheological methods for yield stress estimation of cement pastes during initial hydrati... more Different rheological methods for yield stress estimation of cement pastes during initial hydration were used and results were compared. These methods include measuring of the hysteresis loop, flow curves (recalculated to the same time of hydration) and large amplitude oscillating strain (LAOS). Experiments were performed with four Ordinary Portland Cements from one manufacturer, produced at different factories and one polycarboxylate acid based superplasticiser (SP). The yield stress values obtained by constructing flow curves is the only method which gives information about the evolution of the rheological properties, reflecting structure evolution of cements pastes. It was shown that the yield stress values established by the LAOS method and that calculated from the flow curves are similar while the values found from the downward part of the hysteresis loops are much lower. Differences in the yield stress values obtained by various methods are related to the different states of t...
Applied Rheology, 2016
The addition of certain ingredients in conventional concrete is essential for improving rheologic... more The addition of certain ingredients in conventional concrete is essential for improving rheological properties of this construction material. The effect of limestone and superplasticisers on the hydration kinetics of self-compacting concrete (SCC) was investigated on cement paste scale. These additives interact mostly with cement paste, since aggregates are considered to be inert materials. The understanding of the effect of these mineral and chemical additives on the hydration kinetics of cement paste is the key to design a self-compacting concrete with great properties. Four CEM I 52.5 N Portland Cements, limestone (LS) and one type of superplasticiser (SP) were used in this research. The hydration kinetics were evaluated by monitoring the storage modulus growth and different coefficients of a self-acceleration kinetics equation were used to depict the effect of different concentrations of SP with and without the optimum concentration of limestone (30%) on the hydration kinetics o...
Engineering Journal: Science and Innovation, 2018
Applied Rheology, 2007
The concentration and size dependencies of elastic properties of highly concentrated w/o emulsion... more The concentration and size dependencies of elastic properties of highly concentrated w/o emulsions were studied. The range of weight concentration of the disperse phase was 90 - 96%, the range of the average droplet size was 16 - 20 mm, and the droplet size distribution remained unchanged. The disperse phase consists of droplets of over-cooled concentrated aqueous solutions of inorganic salts. The concentration range being studied lies above the limit of maximal close packing, j > jm. The droplet size distribution is fairly wide and the shape of droplets is polygonal. These factors alone determine possible new rheological effects, such as the elasticity and visco-plastic behaviour of emulsions, as well as the observed form of concentration and size dependencies of rheological properties of emulsions. The complete flow curves were measured for these fairly new emulsion systems. It emerged that they were similar to the entire concentration and droplet size ranges being studied. The...
Applied Rheology, 2004
The answer to this provocative question is “no”! This is demonstrated by experiment and analysis ... more The answer to this provocative question is “no”! This is demonstrated by experiment and analysis for two very different materials – a highly concentrated emulsion and an 8%v/v Kaolin clay suspension. The flow curves of both materials clearly showed a low shear Newtonian asymptote and a pseudoplastic domain. The difference in the accuracy of the fitting equations relates mainly to the low shear rate domain. While the Cross equation is adequate over the full flow curve, the power law and the Herschel-Bulkley equations are clearly inadequate for the low shear rate range. These equations as well as the direct numerical method (using the Rabinowitsch-Weissenberg integral) were used for the calculation of the laminar pipe flow transport characteristics and the results were compared with experimental pipe flow data. It was shown that in all cases the maximum error did not exceed 5%, which is quite acceptable for engineering design, indicating that the choice of the flow curve fitting equat...
Colloid Journal, 2014
The study of the viscoelastic properties of composites based on road bitumens have shown that the... more The study of the viscoelastic properties of composites based on road bitumens have shown that the addition of polymeric modifiers (poly(bytadiene block styrene) or devulcanized rubber particles) substan tially increases the storage and loss moduli and decreases the intensity of reduction in the storage modulus with temperature by several orders of magnitude. However, at high polymer content, growth inadmissible from the point of view of acceptable technological parameters is observed in the apparent viscosity. The intro duction of carbon nanotubes into bitumen does not substantially affect its viscoelastic properties. Filling with meta kaolin promotes an increase in the storage modulus at elevated temperatures. It has been shown that a direct correlation may be established between the objective characteristics of bitumen based composites and standard specification parameters, such as penetration depth and heat resistance.
Colloid Journal, 2008
Critical comparison of dependences of elastic and plastic properties of highly concentrated emuls... more Critical comparison of dependences of elastic and plastic properties of highly concentrated emulsions (so-called "compressed" emulsions) on the concentration and droplet sizes is performed. The studied emulsions of water-in-oil type are so-called "liquid explosives." They are characterized by different mean sizes and different droplet size distributions of the dispersed phase. Different average values (D av , D 32 , and D 43) are used as characteristics of droplet sizes. Experiments are carried out with emulsions of two concentrations. Aqueous phase (dispersed droplets) is presented by supercooled solutions of inorganic salt in water in a metastable state. The concentration limit of the existence of highly concentrated emulsions is determined by the condition of the closest packing of liquid droplets, which lies in the * = 0.77-0.80 range. In addition, there is a limiting value of the maximal size of droplets. This limiting value depends on the concentration and meets the requirement that droplets should be small enough for the solution to exist in a supercooled state. The elastic modulus and the yield stress of emulsions studied are proportional to the square of the reciprocal linear size of droplets, which contradicts some theoretical models, according to which these parameter should be proportional to the reciprocal size of droplets. Using the obtained experimental data, we constructed generalized dependences of the elastic modulus and the yield stress on the concentration and size of droplets. These characteristics are in good agreement with the experimental data.
Rheologica Acta, 1995
Different non-linear phenomena (such as non-Newtonian flow, large elastic deformations, instabili... more Different non-linear phenomena (such as non-Newtonian flow, large elastic deformations, instabilities of different types and many others) are the heart of theology. Therefore many attempts were carried out to find quantitative, or at least qualitative, models of non-linear behavior. The general or perhaps most attractive way of developing rheological constitutive equations consists in the search for the most general method to describe everything in the framework of a single approach. Naturally, this leads to very complicated and ambiguous equations. Meanwhile, it is reasonable to try another way based on separating observed phenomena into different types depending on observed phenomena into different types depending on their physical origin. An attempt to propose such their physical origin. An attempt to propose such classification of nonlinear rheological effects is made. According to the assumed scheme three levels of non-linearity are distinguished. There is a group Key words Finite deformationsnon-Newtonian equations-nonlinearity-constitutive equations-elastic potential-neckingphase transitions-melt fracture instabilities
Rheologica Acta, 1969
This paper deals with slow processes of extension of an elasto-viscous cylinder under conditions ... more This paper deals with slow processes of extension of an elasto-viscous cylinder under conditions where the theory of linear viscoelasticity is applicable. Kinematic dependences are given and four nonstationary problems are solved concerning the extension of a cylinder when one of the following parameters is constant: strain rate, extension rate, stress, and tensile force. Experiments were performed on a low-molecular polyisobutylene at 25 ~ and constant extension rates. The changes in total deformation and stresses, and after unloading, in highly elastic and irreversible deformation, were determined. The effect of the forces of surface tension on the elastic recovery of the samples was taken into account. The formulas of the linear theory of viscoelasticity are shown to apply within the range of extension rates studied. The viscosity and rubbery elasticity modulus were determined and found to agree well with the results obtained during steady shear flOWS.
Rheologica Acta, 2010
A set of highly concentrated water-in-oil y0 ∼ /d 2 scaling, although the experimental results em... more A set of highly concentrated water-in-oil y0 ∼ /d 2 scaling, although the experimental results 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 v ∼ γ 1/2 scaling, a modified version of Windhab model was suggested which showed excellent fitting of experimental results. The linear dependences of y0/ 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 for different surfactants were not superimposed.
Polymer Science Series A, 2011
Journal of Non-Newtonian Fluid Mechanics, 2013
For more than 20 years it has been debated if yield stress fluids are solid below the yield stres... more For more than 20 years it has been debated if yield stress fluids are solid below the yield stress or actually flow; whether true yield stress fluids exist or not. Advocates of the true yield stress picture have demonstrated that the effective viscosity increases very rapidly as the stress is decreased towards the yield stress. Opponents have shown that this viscosity increase levels off, and that the material behaves as a Newtonian fluid of very high viscosity below the yield stress. In this paper, we demonstrate experimentally (on four different materials, using three different rheometers, five different geometries, and two different measurement methods) that the low-stress Newtonian viscosity is an artifact that arises in non steady state experiments. For measurements as long as 10 4 seconds we find that the value of the 'Newtonian viscosity' increases indefinitely. This proves that the yield stress exists and marks a sharp transition between flowing states and states where the steady state viscosity is infinite-a solid!
International Journal of Polymeric Materials, 1982
Abstract An analysis is presented of the principal rheological factors inherent in the flow of ne... more Abstract An analysis is presented of the principal rheological factors inherent in the flow of nematic solutions of rigid-chain aromatic poly(para-amides), viz., viscosity anisotropy, yield points, and viscosity peaks in the region of phase transition on the temperature and the concentration scale, thereby making it possible to use the rheological characteristics to plot phase diagrams.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
An investigation was performed into the effect of surfactants on the rheology of water-in-oil hig... more An investigation was performed into the effect of surfactants on the rheology of water-in-oil highly concentrated emulsions (HCE). The surfactants were oligomers of the PIBSA-type with different headgroups and low-molecular-weight sorbitan monooleate (SMO). The rheological properties of HCE are presented by flow curves with clearly expressed yield stress and dynamic modulus which does not depend on frequency but does on the amplitude of deformations. The changes in modulus and the yield stress depend on the nature of the headgroups as well as the addition of low molecular weight surfactant. It was shown that an increase in the surfactant concentration results in the decrease in the rheological parameters. This shows the significance of micellar structure on the rheological behaviour of HCE. The dependencies of elastic modulus as well as the yield stress on droplet size are deviated from scaling by Laplace pressure. This means that some additional arguments to explain the elasticity of HCE emulsions should be included for comparison with the classical models based on the conception of increase in the surface area of droplets. Finally, it was found that the scaling of shear modulus with reciprocal squared droplet size fulfil the zero intercept condition for this variation.
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Papers by Alexander Malkin