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The manufacturing of paper with new functional properties is a current problem today. A method of modifying the surface layer of paper by the partial dissolution of cellulose on its surface is proposed. N-Methylmorpholine-N-oxide (NMMO) is proposed for use as a solvent, the regeneration of which provides an environmentally friendly process. It was shown that among the possible hydrate forms of the solvent, the monohydrate and higher-melting forms are optimal for modifying the paper surface. The temperature–time modes of processing were revealed and the weight gain and density increase in the course of modification were estimated. The structural and morphological features of the original and modified paper were studied by X-ray imaging and scanning microscopy. The NMMO surface treatment makes it possible to vary the air permeability of the paper, making it practically non-permeable. The capillary and pore system were radically transformed after the partial dissolution of cellulose and its coagulation, as the formed cellulose film isolates them, which leads to a decrease in surface absorbency. The processing conditions allowing for the optimization of the optical and strength properties of the modified paper samples are revealed. The resulting paper with a modified N-methylmorpholine-N-oxide surface layer can be used for printing valuable documents.

Evolution of the morphology of cellulose solutions in N-methylmorpholine-N-oxide during coagulation with a “soft” coagulant, isobutyl alcohol, at different temperatures is considered. Using optical interferometry and transmitted and scanning electron microscopy the mechanism of phase separation of the system to form a polymer phase is studied depending on the temperature of alcohol. It is shown that, in the case of a room temperature coagulant, a heterogeneous film with a droplet texture enlarging over thickness appears along the precipitation front. At a high temperature of alcohol the coagulation of the solution occurs in two stages. At the first stage the penetration of the coagulant into the jet of spinning solution leading to the formation of vacuoles occurs. The phase separation of the solution proceeds within the vacuoles as microreactors to form a polymer-concentrated shell and a polymer-diluted phase in the vacuole cavity. At the second stage the coagulant diffuses through the vacuole shell into the bulk of the solution and causes its uniform coagulation. The process of vacuole formation is visualized. The transverse cleavage of the film is analyzed by energy dispersive X-ray spectroscopy. The difference in the content of C, N, and O atoms on the walls of vacuoles and in the region of a film with a uniform cellular morphology is established.

The kinetics of formation of a three-dimensional structure in compositions based on butyl rubber and silicon-containing hyperbranched polymethylsilsesquioxanes and MQ copolymers is studied in comparison with compositions containing common dispersed phases: carbon black and silica. Features of the chemical structure of the synthesized organosilicon polymers make it possible to treat the morphology of their elementary particles as core–shell. The role of an inorganic “core” is played by silica structures, whereas methyl shells should ensure compatibility with the carbochain matrix of the rubber. Quinol ether is used as an agent of crosslinking via double bonds of the isoprene part of the rubber. The crosslinking process is carried out in the mode of continuous heating of compositions with registration of thermal effects by differential scanning calorimetry and dynamic moduli by oscillatory rheometry. The apparent activation energies of the process of chemical crosslinking under nonisothermal conditions are calculated in terms of various models. It is shown that the apparent activation energy of crosslinking is lower for filled systems. This indicates that rubber macromolecules are partially uninvolved in chemical crosslinking as a result of adsorption and loss of relaxation mobility. The adsorption activity of fillers is estimated from a difference in the activation energies of the initial rubber and filled compositions; this parameter is the lowest for polymethylsilsesquioxanes.

The process of solid-phase dissolution of polyacrylonitrile copolymer containing ionic sulfo groups in an electron-donating solvent, N-methylmorpholine-N-oxide, is studied depending on its crystal hydrate form and preparation conditions. Optical studies of the transition of solid-phase copolymer–solvent systems to a viscous flow state make it possible to construct solubility curves and reveal stages of morphological transformations during dissolution, explaining their nature. Solid-phase mixed systems are studied by IR spectroscopy, and interactions of the functional groups of the copolymer with various crystal hydrates of the solvent are analyzed both during standard mechanical mixing and mechanochemical activation under intense shear deformation, which predetermines the formation of solid solutions.

The review is devoted to the fundamental problems of physical chemistry and rheology posed in the analysis of stability loss of polymer jets in extension. Studies of phenomena occurring in deformation of polymeric fluids are of considerable applied interest because extension of polymeric fluids underlies many industrial processes, first of all, fibre spinning. Studies of critical conditions of deformation are based on general principles of fluid mechanics, which are applicable to all fluids and various phenomena in nature and technology. First we discuss solutions to classical problems of instability of liquid jets as the basis for further analysis of the behaviour of polymeric fluids in particular situations. Next, specific features of the deformation mechanisms and appearance of instabilities of polymeric fluid jets are considered as consequences of their physicochemical and rheological properties. The bibliography includes 162 references.

The rheological properties of concentrated suspensions containing 55 and 60 vol % aluminum particles are studied. This concentration range corresponds to the transition from the viscoelastic to the elastoplastic behavior of the suspensions. Moreover, this range is most favorable for powder injection molding of metals and ceramics. The measurements are performed in a rheometer at different shear stresses. Elastoplastic deformations take place at low stresses, while separation, i.e., the rupture of the adhesion contact between the bulk suspension and the boundary of a solid wall of the rheometer, is observed with an increase in the stress. The rupture of the adhesion contact occurs with time, and this process is characterized by a dependence of the lifetime (durability) of the contact on stress. This dependence is of an exponential character. The replacement of smooth working surfaces of the rheometer by rough ones leads to some increase in the stresses. This reflects the replacement of the adhesion separation by the formation of discontinuities in the bulk suspension at the asperities of the rough surface. The observed behavior of the concentrated suspensions in the aforementioned range of compositions is represented by a mechanical model, into which a new element has been introduced. It is represented by a friction pair with variable length (and, accordingly, variable friction force). The spurt arises when a threshold force that induces displacement over the friction surface is reached.

Silicone resins are hyperbranched macromolecules, which are nearly spherical in shape, nanometer in size, and covered with numerous terminal organic groups. For this reason, they can play a role of functionalized silica nanoparticles that are miscible with a polymer medium. In this paper, mixtures of linear polyisobutylene (PIB) with methyl-terminated silicone MT resin are considered. The phase states of mixtures were studied by laser interferometry method accompanied with rheological tests. It turned out that the solubility of the silicone resin in PIB matrix does not exceed a few percent even at high temperatures. Nevertheless, the addition of the resin significantly reduces the effective viscosity of PIB due to the shear-induced interlayer slip. To describe the concentration dependence of the blend viscosity, various empirical equations were considered, and their combination to describe the viscosity of blends in different phase states by one equation was proposed.

A new method is developed for the production of composite fibers based on cellulose and vinyltriethoxysilane and formed from N-methylmorpholine-N-oxide solutions. Introduction of the organosilicon additive promotes the activation of cellulose pyrolysis processes, and its choice relies on the presence of a double bond in vinyltriethoxysilane, which can be opened when the temperature rises. Mixed solutions are emulsions with labile droplets of the organosilicon liquid that easily change their shape under deformation. The study of the rheological behavior of the mixed solutions of cellulose with vinyltriethoxysilane reveals an unusual character of a change in viscosity with the concentration of vinyltriethoxysilane—with a minimum at 10–15%. From joint solutions by the dry-jet wet method, composite fibers are spun in an aqueous coagulation bath at a rate of 50–70 m/min. The study of their thermal properties shows that in thermolysis vinyltriethoxysilane additives catalyze condensation processes in cellulose and lead to an increase in char yield. Using IR spectroscopy, the combined chemical transformations of cellulose and vinyltriethoxysilane at all stages of the heat treatment of composite fibers up to 1200°C are analyzed for the first time. It is found that during thermolysis the chemical interaction of vinyltriethoxysilane with cellulose occurs and carbon fibers “crosslinked” by silicon carbide fragments are formed.

A series of new wholly aromatic (co)polyesters based on m-substituted bifunctional comonomers—4′-hydroxybiphenyl-3-carboxylic (3HBCA) and 3-hydroxybenzoic (3HBA) acids with molar ratios of 3HBCA:3HBA from 0:100 to 60:40, respectively—was synthesized. NMR and FTIR spectroscopy methods proved the full compliance of the copolymer composition with the target ratio of comonomers, as well as high compositional homogeneity (absence of block sequences). The resulting copolyesters have a sufficiently high molecular weight and their intrinsic viscosity values are in the range of 0.6–0.8 dL/g. Thermal analysis showed that all 3HBCA-3HBA copolyesters are amorphous, and with an increase in the content of biphenyl units (3HBCA), the glass transition temperature increases significantly (up to 190 °C). The onset of the intense thermal decomposition of the synthesized polyesters occurs above 450 °C. Thus, this indicates a sufficiently high thermal stability of these polyesters. Rheological measurements have shown that melts of copolyesters with a high content of 3HBCA units exhibit anisotropic properties. At the same time, the method of polarization optical microscopy did not confirm the transition to the liquid crystal state for these polyesters. These results confirm that it is possible to obtain high-performance polyesters based on 3HBCA, but not a mesogenic comonomer. Thus, 3HBCA is a promising comonomer for the synthesis of new thermotropic copolyesters with controlled anisotropic properties.

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.

The influence of alkyl acrylate comonomers in the rank of methyl- (MA), butyl- (BA), ethylhexyl- (EGA), and lauryl- (LA) in ternary copolymers based on acrylonitrile, alkyl acrylate and acrylamide (PAN-alkyl acrylate) on their solutions rheological behavior in dimethyl sulfoxide (DMSO), and mechanical properties of the spun fibers have been investigated. To reveal the role of molecular weight, two series of copolymers with molecular weights of ~50 and 150 kg/mol have been studied. It was shown that the nature of the alkyl acrylate does not significantly affect the rheological behavior of their solutions regardless of the length of the alkyl substituent and the content of the alkyl acrylate in copolymers. An exception is the high-molecular PAN-LA, which is characterized by a non-Newtonian behavior at lower concentrations. Two series of fibers were spun from the characterized ranks of low and high-molecular-weight copolymer solutions. For all copolymers, a 2.5–5-fold increase in the strength and elastic modulus of the fiber was found with an increase in Mw. It has been shown that PAN-MA and PAN-LA fibers have a tensile strength of 800 MPa that is 1.5–3 times higher than that of other copolymers spun in the same conditions.

The review summarizes recent advances in the production of carbon fiber precursors based on melt-spun acrylonitrile copolymers. Approaches to decrease the melting point of polyacrylonitrile and acrylonitrile copolymers are analyzed, including copolymerization with inert comonomers, plasticization by various solvents and additives, among them the eco-friendly ways to use the carbon dioxide and ionic liquids. The methods for preliminary modification of precursors that provides the thermal oxidative stabilization of the fibers without their melting and the reduction in the stabilization duration without the loss of the mechanical characteristics of the fibers are discussed. Special attention is paid to different ways of crosslinking by irradiation with different sources. Examples of the carbon fibers preparation from melt-processable acrylonitrile copolymers are considered in detail. A patent search was carried out and the information on the methods for producing carbon fibers from precursors based on melt-spun acrylonitrile copolymers are summarized.

AB-polybenzimidazole (ABPBI) dissolution kinetics in an eco-friendly complex acid-free solvent based on dimethyl sulfoxide (DMSO), methanol and KOH, and the rheological behavior of their solutions are investigated. The optimal component ratio of solvent providing the complete ABPBI dissolution is determined. Methanol containing dissolved KOH contributes to the creation of a single-phase superbasic medium, which accelerates and improves the polymer solubility in a mixture with DMSO, significantly reducing the viscoelasticity of the resulting solution. The optimum methanol content is up to 60 wt.% related to DMSO. The polymer dissolution rate increases by 5 times in this composition. It found the polymer concentration of 9% is close to the dissolution limit due to the strong solution structuring, which is probably associated with an increase in the amount of water released during the KOH-methanol-DMSO interactions. As a result, the conditions for obtaining high concentrated solutions in a complex, mainly organic solvent for fiber spinning are developed. The viscoelastic properties of solutions are measured in the concentration range of 1–9% at temperatures of 20–50 °C. The flow activation energy for 7 and 9% solutions decreases by 1.5 and 2.3 times, respectively, as the content of methanol in the complex solvent increases from 10 to 60%.

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 technological practice. The obtained sintered ceramic samples have quite acceptable mechanical properties of the usual corundum articles.

The viscoelastic characteristics (frequency dependences of the components of the two-dimensional complex dynamic modulus) of interfacial layers formed by polymer solutions on liquid surfaces are measured using a newly-designed instrument. The operation of the instrument is based on the use of a Langmuir trough and a new fast-response system for precise measurement of forces in a surface plane at Boussinesq numbers smaller than ten. Examples are presented to illustrate the abilities of the instrument: the measurement of dilatational dynamic elasticity moduli, the determination of the kinetic parameters of polymer solution spreading at interfaces, and the measurement of the moduli for layers of polymer solutions with different concentrations on solvent surfaces in compression–expansion cycles.

The kinetics of spreading of aqueous hydroxypropyl cellulose (HPC) solutions with different concentrations over a water surface and the rheological properties of films formed at the water–air interface have been studied. The performed experiments are distinguished by the fact that the solvent in the polymer solutions is identical to the liquid subphase, while, beginning from a certain concentration, the aqueous HPC solutions are capable of forming a liquid-crystalline phase. The chosen initial polymer solution concentrations correspond to different regions of the phase diagram for the HPC–water system. The contact of a solution droplet with water yields a time-stable spot of an HPC solution layer. In spite of the fact that some solution concentrations correspond to the existence range of a lyotropic liquid-crystalline phase, an isotropic layer is formed on the water surface irrespective of the concentration and phase state of the solution in the droplet. The dynamic dilatational storage modulus of such an interfacial layer at a frequency of 0.03 Hz is equal to 43 ± 2 mN/m; i.e., it almost coincides with the surface tension of the formed interfacial layer.

A series of experiments has been carried out in order to construct a master curve generalizing the combined impact of temperature and low viscosity additives on the viscosity of heavy crude oil. Th...

The rheological properties of aluminum suspensions in low-molecular-weight poly(ethylene glycol) have been systematically studied within a wide range of concentrations up to the ultimate content of the solid phase (about 70%). As the concentration of dispersed particles is increased, the rheological properties evolve from a Newtonian fluid to an elastoplastic solid. In the region of the flowable state, the studied dispersions have no yield stress. However, above a certain concentration, which is considered to be a mechanical glass transition, the suspensions become non-flowable. At higher concentrations, a region of elastoplastic state of highly concentrated systems arises, which has not yet been considered as we know. The boundaries of this region have been determined and the dependences of the characteristics of elasticity and plasticity on stress have been obtained. This region corresponds to the ultimate degrees of filling and is of importance for contemporary additive technologies and so-called “powder injection molding .”

Fibers of bacterial cellulose were obtained for the first time from solutions in N-methylmorpholine N-oxide (NMMO) by using the concept of solid-phase dissolution of bacterial cellulose. The mechanism of solid-phase dissolution of bacterial cellulose in NMMO is examined with due regard to the structural and morphological characteristics of native bacterial cellulose. By investigating the structure of the fibers it was possible to reveal the different orientation of the main diffraction planes of the outer shell and inner part of the fiber reflecting the structural aspect of the shell–core morphology. The fibrillar morphology of the fiber was established by scanning electron microscopy. The thermal characteristics of the fibers of bacterial cellulose differ radically from the characteristics of fibers of plant origin in the preponderance of condensation processes that produce exo effects on the thermograms and lead to increase of the carbon residue. The mechanical characteristics of the obtained fibers were characterized.

The process of film formation including the initial treatment of thin layers of cellulose solutions in N-methylmorpholine N-oxide with isobutanol followed by washing with water is investigated in detail, and the structural and morphological features of the obtained films are examined. The phase state of the N-methylmorpholine N-oxide–isobutyl alcohol system is studied by differential scanning calorimetry and optical interferometry, and a diagram describing the crystalline equilibrium and allowing determination of the temperature–concentration “window” of compatibility of components is constructed. The dependence of viscosity of N-methylmorpholine N-oxide solutions in isobutanol on temperature confirms the phase composition of the system. The process of film formation is modeled by analyzing the diffusion zone of the cellulose solution–isobutyl alcohol system. The IR study of the interaction of N-methylmorpholine N-oxide containing 13.3% water with isobutanol shows that the affinity of isobutanol for water is much higher than that for N-methylmorpholine N-oxide. For this reason, when the spinning solution is brought in contact with isobutanol, the redistribution of water between the interacting components occurs and the structure of the heterogeneous gel-like complex cellulose–N-methylmorpholine N-oxide–isobutanol “is frozen,” as proved by the X-ray diffraction study of the films. Complete removal of the solvent and isolation of cellulose from this film proceed only upon subsequent washing with water. The X-ray diffraction and optical interferometry study of the effect of temperature on the interaction of a hot cellulose solution with cold isobutanol suggests that at room temperature the film obtained from solution contains inclusions of the vitrified N-methylmorpholine N-oxide. Under isothermal conditions (at a temperature of 90°С), the rate of interdiffusion grows appreciably and the solution preserves the homogeneous structure. Thus, the precipitation of cellulose from the bicomponent solvent N-methylmorpholine N-oxide–water upon contact first with isobutanol and then with water proceeds via two stages: initially the system undergoes phase separation and a concentrated solution is formed in the isobutanol-N-methylmorpholine N-oxide blend, from which cellulose precipitates upon interaction with water. When the process of primary interaction of the solution with alcohol is conducted under the conditions of compatibility of isobutanol with N-methylmorpholine N-oxide, a more homogeneous morphology of the films can be obtained.

Solid–state dissolution in N–methylmorpholine N–oxide was used to obtain solutions of mixtures derived from cellulose and various organosilicon additives, namely, tetraethoxysilane, vinyltriethoxysilane, and bis (trimethylsilyl)acetylene. Optical study of the phase composition and morphology of these solutions showed that they are two–phase emulsions with a rather broad size distribution of particles of the dispersed phase. The nature of the flow of the mixed systems in continuous and dynamic deformation when the rheological behavior is monotypic depends to a certain extent on the nature of the organosilicon additive. Dry wet–jet spinning was used to obtain composite fibers. The structure and morphology of these fibers were studied as well as their mechanical and thermal properties. Analysis of the x–ray patterns diffractograms of the cellulose and composite fibers showed that the introduction of organosilicon additives into the cellulose matrix leads to less structural ordering of the cellulose. The mechanical characteristics of the composite fibers show some decrease in the strength and deformation characteristics with an increase in the elastic modulus in comparison with the cellulose fibers. Heat treatment of the cellulose and composite fibers up to 1000°C revealed a significant increase in the mass of carbon residue, whose amount depends on the type of additive.

The compatibility of tetraethoxysilane (TEOS) with polyacrylonitrile (PAN) solutions in dimethyl sulfoxide, the morphology of the mixed systems, and their rheological behavior have been analyzed. The combination of interferometry, refractometry, and optical microscopy has been employed to study the phase equilibrium realized in mixtures of TEOS with dimethyl sulfoxide and a PAN solution and to plot phase diagrams, which have indicated that TEOS is soluble in the PAN solution up to TEOS concentrations of 10–11%. As the TEOS content is increased within a concentration range of 10–20%, an emulsion with droplet sizes up to 40 µm is formed. At higher TEOS concentrations, the macroscopic separation of the system takes place. It has been shown with the use of rotational rheometry that, in the range of solutions, the presence of TEOS leads to a decrease in their viscosity and elasticity, while the viscosity increases in the range of emulsification. The analysis of the dynamic data has, for the first time, shown the bifurcation of the dependences of the storage modulus on the loss modulus at the point of phase separation. The calculation of the characteristic relaxation time of the ternary system and the dependence of this time on TEOS concentration has indicated a dramatic growth of the relaxation time in the region of emulsification, with this growth being determined by the relaxation properties of interfaces. Considering the obtained systems as a raw material for producing composite fibers, a solution droplet has been used to simulate the effect of TEOS on the kinetics of coagulation of PAN solutions with precipitants having different activities. It has been shown that, depending on TEOS concentration, the precipitation may yield gels with the content of this organosilicon additive either uniformly or nonuniformly distributed over the hypothetic cross section of a fiber.

The study of different colloidal and polymeric fluids by rotational rheometry has shown that their shear deformation may be accompanied by oscillations of three types. Oscillations of the first type result from the influence of controlling or measuring systems of an instrument and are observed in a stress range of 0.01–0.1 Pa, although the elasticity of a fluid may substantially increase this threshold. Oscillations of this type arise in all regimes of measurements; however, they make an essential contribution only when the rheological properties of low-viscosity fluids or viscoelastic systems are measured near the yield stress. These instrumental oscillations represent an artifact that is not related to the properties of an object under examination. Oscillations of the second type result from the slip/stick effect upon the contact between a solid working surface of an instrument and the surface of a studied viscoelastic material. Such oscillations are observed at relatively high shear rates of moving various materials that may form solidlike structures. In particular, oscillations of this type are of special importance in the case of gels. Oscillations of the third type are due to volume effects and reflect structural bifurcations at rather high shear stresses (substantially higher than possible experiment errors). Such oscillations reflect periodic structure formation/disruption in multicomponent systems, such as, e.g., concentrated suspensions. The amplitude of these oscillations depends on the elastic properties of studied systems. “Superposition” of different reasons, which cause the oscillations observed in the course of testing multicomponent systems, is also possible.

A series of novel copolyesters based on polyethylene terephthalate (PET) and 4′-hydroxy-biphenyl-4-carboxylic acid (HBCA) was obtained by melt polycondensation of bis(2-hydroxyethyl) terephthalate and 4′-acetoxybiphenyl-4-carboxylic acid (ABCA) as co-monomers with Sb2O3 as a catalyst. Using this synthetic procedure, a set of copolymers containing 20–80 mol% of HBCA units was prepared. According to NMR spectroscopy, the copolymers were of random composition. Copolyesters comprising 60–80 mol% of HBCA possessed increased heat resistance and formed nematic melts at 270 °C and higher. The liquid crystal (LC) phase formation was accompanied by transition to non-Newtonian characteristics of the melt flow, as well as an equalization of storage and loss moduli values. According to XRD and polarizing microscopy, the LC glassy phase of the copolyesters coexists with crystalline regions of poly-(4′-hydroxy-4-biphenylcarboxylate), non-melting up to 400 °C and above. The mechanical characteristics of these LC copolyesters showed similar or better values than those of well-known LC polymers. These novel copolyesters can be useful in obtaining heat-resistant materials with an ordered structure and, as a consequence, improved performance.

The effect of temperature and storage time at a constant temperature on the stability of poly-(o-aminophenylene)naphthoylenimide solutions in N-methylpyrrolidone has been analyzed using rotational rheometry. A temperature&ndash, time window beyond which an irreversible change in the viscoelastic properties of solutions due to cumulative reactions of continuous polymerization and possible intramolecular cyclization has been detected. The influence of polymer concentration and its molecular weight on the rheological properties of solutions determining the choice of methods for their processing into fibers and films has been investigated. The effect of non-solvents (water and ethanol) additives on the rheological properties of solutions and the kinetics of their coagulation has been studied. Dosed addition of non-solvent into the solution promotes a significant increase in the viscoelasticity up to gelation and phase separation. Non-solvent presence in the polymer solutions reduces the activity of the solvent, accelerates the movement of the diffusion front at coagulation, and minimizes the number of macro defects. The combination of parameters under investigation renders it possible for the first time to develop new principles modifying dopes for wet spinning into aqueous or ethanol coagulation bath and finally to obtain a heat- and fire-resistant polynaphthoylenebenzimidazole fibers.

The dynamics of a straight section of a jet arising during the electrospinning of a polymer solution without entanglements, and the orientation of polymer chains in the jet were explored based on the analysis of the forces balance equation and the rheological equation of the finitely extensible nonlinear elastic model. Two modes of the jet behavior were predicted. At relatively low volumetric flow rates, the straight jet has a limited length, after that, its rectilinear motion becomes impossible, while at higher flow rates, the jet always remains straightforward. It is shown that polymer chains in a jet can be strongly stretched, which leads to phase separation in a spinning solution. Aggregation of the stretched chains was also studied and the parameters of the emerging inhomogeneous structure were predicted.

Replacing the aqueous coagulation bath with an alcoholic one during spinning cellulose fibers (films) from solutions in N-methylmorpholine-N-oxide leads to a radical restructuring of the hydrogen bonds net of cellulose and, as a result, to a change in the structure and properties of the resulting material. By the method of optical interferometry, it was possible to identify the intrinsic features of the interaction of the solvent and isomeric alcohols and to construct phase diagrams of binary systems describing the crystalline equilibrium. Knowledge of the phase states of the system at different temperatures renders it possible to exclude the process of solvent crystallization and conduct the spinning in pseudo-homogeneous conditions. The structure and morphology of samples were studied using X-ray diffraction and scanning electron microscopy methods for a specific coagulant. When the solution under certain conditions is coagulated at contact with alcohol, the solvent may be in a glassy state, whereas, when at coagulation in water, an amorphous-crystalline structure is formed. The structural features of cellulose films obtained by coagulation of solutions with water and alcohols help to select potential engineering or functional materials (textile, packaging, membranes, etc.), in which their qualities will manifest to the best extent.

The influence of introducing acrylic acid (AA) into the reaction mixture with acrylonitrile at the synthesis of copolymers by free-radical polymerization (FRP) and radical polymerization with reversible addition&ndash, fragmentation chain transfer (RAFT) on the rheological properties of their solutions in dimethyl sulfoxide, as well as on the capability to spin fibers by the mechanotropic method, is analyzed. The influence of AA dosing conditions on the rheological properties of the solutions in the concentration range above the crossover point was not revealed. In the case of RAFT synthesis, the rheological properties differ distinctively in the high concentration region that is expressed by unusual viscoelastic characteristics. Dilute solution viscometry revealed the influence of the comonomer loading order on the interaction intensity of the copolymer macromolecules with a solvent, which is more pronounced for samples synthesized by FRP and can be associated with the copolymers&rsquo, molecular structure. Fiber spinning from solutions of polyacrylonitrile and its copolymers (PAN) synthesized by the RAFT method was not able to achieve a high degree of orientation drawing, while for polymers with a wider molecular weight distribution synthesized by FRP, it was possible to realize large stretches, which led to high-quality fibers with strength values up to 640 MPa and elongation at a break of 20%.

Concentrated metal-in-polymer suspensions (55 vol.% and 60 vol.%) of aluminum powder dispersed in low molecular weight polyethylene glycol) demonstrate elastoplastic properties under compression and shear. The rheological behavior of concentrated suspensions was studied in a rotational rheometer with uniaxial compression (squeezing), as well as shearing superimposed on compression. At a high metal concentration, the elasticity of the material strongly increases under strain, compared with the plasticity. The elastic compression modulus increases with the growth of normal stress. Changes in the shear modulus depend on both normal and shear stresses. At a low compression force, the shear modulus is only slightly dependent on the shear stress. However, high compression stress leads to a decrease in the shear modulus by several orders with the growth of the shear stress. The decrease in the modulus seems to be rather unusual for compacted matter. This phenomenon could be explained by the rearrangement of the specific organization of the suspension under compression, leading to the creation of inhomogeneous structures and their displacement at flow, accompanied by wall slip. The obtained set of rheological characteristics of highly loaded metal-in-polymer suspensions is the basis for understanding the behavior of such systems in the powder injection molding process.

Bacterial cellulose as polysaccharide possessing outstanding chemical purity and a unique structure compared with wood cellulose, attracts great attention as a hydrocolloid system. It was shown, that at intense mechanical action on a neat bacterial cellulose film in presence of water, the gel-like dispersions are obtained. They retain stability in time (at least, up to several months) and temperature (at least, up to 60 &deg, C) without macro-phase separation on aqueous and cellulose phases. The main indicator of the stability is constant viscosity values in time, as well as fulfilling the Arrhenius dependence for temperature dependence of viscosity. Flow curves of diluted dispersions (BC content less than 1.23%) show strong non-Newtonian behavior over the entire range of shear rates. It is similar with dispersions of micro- and nanocrystalline cellulose, but the absolute viscosity value is much higher in the case of BC due to more long fibrils forming more dense entanglements network than in other cases. Measuring the viscosity in increase and decrease shear rate modes indicate an existence of hysteresis loop, i.e., thixotropic behavior with time lag for recovering the structural network. MCC and NCC dispersions even at cellulose content more than 5% do not demonstrate such behavior. According to oscillatory measurements, viscoelastic behavior of dispersions corresponds to gel-like systems with almost total independence of moduli on frequency and essentially higher values of the storage modulus compared with the loss modulus.

Rheological and morphological properties of heavy crude oil-in-water (O/W) emulsions have been studied. Two series of emulsions were considered: first, the surfactant type remained constant, while the continuous phase content was varied and second, the surfactant type was varied while the continuous phase content remained constant. Under stress-controlled shearing, all samples exhibit viscoplastic behavior. The rheological properties are directly related to the morphology of the emulsions which vary in size of dispersed phase droplets and their inherent structure. Adding a surfactant characterized by a high value of interfacial oil-water tension results in a decrease in the yield stress (which is a measure of the interparticulate structure strength). The same effect is attained by increasing the water content. Meanwhile, these two factors determine the viscosity which can be much lower than that of the basic heavy crude oil if the O/W type of emulsions has been created. Special attention was paid to the viscoelastic properties which have been scarcely reported. Correlations were found between the surfactant properties, composition of the emulsion, and rheological characteristics of emulsions (yield stress, apparent viscosity, and viscoelastic properties), which allows for reduction in the crude oil viscosity down to a low enough level acceptable for pipe transportation.

In the present study, one of the possible methods of the bacterial cellulose processing is proposed via its dissolution in N-methylmorpholine-N-oxide using the stage of mechano-chemical activation of the solid polymer&ndash, solvent system. Preliminary solid-phase activation is apparently a decisive factor affecting the dissolution rate of bacterial cellulose in N-methylmorpholine-N-oxide. The effects of bacterial cellulose concentration, solvent nature, degree of polymerization and temperature on dissolution time were studied. The rheological behavior of the solutions does not change at 120 &deg, C for at least half an hour that allowed us to process such solutions for films preparation. The films from these solutions by means of dry-wet jet spinning in aqueous coagulant were formed. The structure of the nascent cellulose and formed films was tested by the X-ray diffraction method and SEM. The thermal behavior of the films revealed an increase in the carbon yield for the formed films compared to the nascent bacterial cellulose. The process of film pyrolysis is accompanied by exothermic effects, which are not typical for wood cellulose. Some reasons of such thermal behavior are considered.

The combined solutions of cellulose and PAN in N-methylmorpholine-N-oxide at total polymer contents of 18 and 25% are obtained by solid-phase dissolution. The investigation of phase composition and morphology of these systems via optical methods shows that the solutions of cellulose and PAN in N-methylmorpholine-N-oxide are incompatible and form emulsions. The action of deformation on the emulsions leads to the appearance of orientational effects. If PAN predominates in droplets of the dispersed phase of cellulose solutions, this leads to the formation of fibrillar structures under shear stress, while in the case of PAN dispersion medium double emulsions are formed, in which internal droplets of the cellulose solution are most easily extended under shear. The rheological behavior of the combined systems is the direct consequence of structural-morphological transformations proceeding during deformation of the system. An analysis of the morphological and rheological features of heterophase systems reveals the concentration interval for the moldability of composite fibers from spinning emulsions.

Series of polyacrylonitrile terpolymers with molecular weights of (7–20) × 104 have been synthesized in dimethylsulfoxide using classical radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of the synthesis method on the rheological behavior of dilute and concentrated solutions of the resulting copolymers has been analyzed. No differences have been found in the viscous properties and viscoelastic behavior of the concentrated solutions in the temperature range of 20–80°C. However, viscometry of the dilute solutions made it possible to detect a difference in the interaction between the solvent and macromolecules of the copolymers obtained by these methods. The copolymers differ in the values of the second virial coefficient, which indicates that the interaction of the solvent and polymer is specific to the synthesis method. This phenomenon seems to be caused by different branching of chains in the copolymer and/or its compositional heterogeneity. For dilute solutions, it was possible to construct a single generalized concentration dependence of reduced viscosity in the coordinates of the Martin equation. Transition to the region of concentrated solutions required an introduction of yet another parameter that describes the effective density of the mesh network, namely, the ratio of the current solution concentration to the crossover concentration. This approach made it possible to construct a generalized dependence of viscosity in the entire concentration range of solutions of polyacrylonitrile copolymers.

A systematic study of the influence of surfactant and stabilizing polymer additives on the rheological properties of heavy oil was carried out. The aim was to optimize the recipe for the most effective reduction in the oil viscosity. A total of 41 versions of the emulsion were prepared using different protocols. Creation of the emulsions with different recipes and modes of mixing led to a regulation of their morphologies, which determined the rheological properties of the final products. In all cases, emulsification resulted in a transformation of the oil from Newtonian behavior to a viscoplastic medium with a blurred yield stress. Dependent upon the composition, the yield stress was decreased up to 0.6 Pa and the viscosity at high shear obtained a value up to 50 mPa s, which is lower than the viscosity of crude oil by 34 times. The efficiency of the viscosity reduction increased with a decreasing temperature.

Carbon—silicon-carbide fibers were produced from cellulose and triethoxyvinylsilane and spun using the solid-phase NMMO-process. Scanning and transmission electron microscopy studies, energydispersive x-ray spectrometry, and x-ray structure analysis of composite carbon fibers established and identified the structure and morphology of carbon fibers that varied from an isotropic shell to regularly organized lamellae of graphite-like layers of the fiber core. Distributions of chemical elements were plotted. The nano-sized dimensions of silicon-carbide regions in the carbon fibers were determined.

A series of model experiments were carried out on drops of poly-(o-aminophenylene)naphthoylenimide (PANI-O) solutions in N-methyl-2-pyrrolidone (NMP) surrounded by a coagulant of different compositions as starting points of defect-free fibers spinning by the wet method. An influence of compositions of dopes and multicomponent coagulants on the diffusion kinetics and drop morphology during coagulation has been investigated. It is shown that the defining parameters of the coagulation process are viscoelastic properties of the polymer solution and the diffusion activity of the coagulant, meaning not only the rate of coagulation but also the presence/absence of macro defects in the resulting fiber. The optimal morphology of as-spun fibers is obtained by coagulation of solution in a three-component mixture containing solvent and two precipitants of different activity (water and ethanol). The chosen coagulating mixture was used for the fiber spinning of PANI-O with different molecular weights dopes, and fibers with sufficiently high strength (~250 MPa), moduli (~2.1 MPa), and elongation at break (50%) were obtained.

The evolution of the morphology of two incompatible polymer melts in a capillary flow was studied using analytical electron microscopy. The spatial distribution of polysulfone and the liquid-crystal (LC) polymer was evaluated by measuring the concentration of sulfur (which is contained exclusively in polysulfone) and oxygen (contained in a much larger proportion in the LC polymer). The distributions of both polymers in the cross-sections of the strands do not change regardless of the specified shear rate, which varies by a factor of 25. However, a thin boundary layer with a width of about 10 μm formed by a low-viscosity LC polymer was detected. Nevertheless, there is a strong deformation and orientation of both polymers. This indicates that the movement of the mixture through the capillary occurs not due to sliding along the boundary layer but also due to shear in the entire volume of the material.

Highly concentrated solutions of acrylonitrile copolymers (PAN) in N-methylmorpholine N-oxide (NMMO) were obtained via the solid-phase activation method. Specific interactions in the system at different stages of the dissolution process starting from solid-state activation and finishing with a transition to a viscous state were studied by IR spectroscopy, polarizing microscopy, interferometry and rheology. It was shown that the crucial factor determining a possibility of dissolution is the complex formation between carboxyl groups in the copolymer and the electron-donor N → O group in the solvent. This complex arises during the process of solid-phase activation of PAN and crystalline NMMO, which thereafter melts and transforms into a homogeneous solution having viscoelastic behavior. In the temperature range of 130–135 °C, irreversible chemical transformations take place in the solutions due to the coherent interaction between nitrile groups; these reactions lead to the formation of cyclic structures and conjugated sequences in the PAN chains. Rheological properties follow this process via specific viscosity and viscoelasticity evolution in time.

Composite fibers were obtained from highly concentrated solutions of cellulose and polyacrylonitrile (PAN) copolymers in N-methylmorpholine-N-oxide (MMO). The processes of co-dissolving cellulose and PAN in MMO and the rheological properties of the resulting composite solutions were examined. It was shown that introduction of PAN into the cellulose matrix affects the structurization processes. Specifically, an increase of the PAN content in the cellulose matrix affects the thermal behavior and mechanical properties of the composite fibers.

The results of a comparative study of the rheological properties of acrylonitrile copolymers solutions synthesized by classical and controlled radical polymerizations in aprotic solvents (dimethyl sulfoxide, dimethylformamide, and dimethylacetamide) are presented. The influence of the chemical nature of comonomers (styrene and acrylamide) and their share in the composition of the chain on the viscosity of solutions is discussed. For all copolymers, the viscosity of solutions is determined by a product of the intrinsic viscosity per concentration. In the transition from dilute and semi-dilute solutions to the concentrated solutions, the form of the dependence changes from linear to power-law. The concentrated solutions are non-Newtonian liquids exhibiting viscoelasticity. Copolymer solutions obtained by controlled radical polymerization have a higher viscosity and less pronounced non-Newtonian behavior. The solutions of copolymers with a high comonomer content obtained in dimethylformamide have the lowest viscosity.

Study of the dynamics of liquid droplets of dilute and semidilute polymer solutions on the surfaces of liquid subphases representing solvents for corresponding polymers has shown that a spot of a rather stable layer is formed on an air–liquid interface. The spot spreads over a liquid subphase surface to yield a monomolecular polymer layer. At the same time, the solvent passes into the solution, so that the polymer or its concentrated solution remains on the subphase surface. The polymer does not dissolve in the bulk subphase for several hours. The stability of the polymer spot has been explained under the assumption that the interfacial surface possesses elastic properties and hinders the penetration of macromolecules into the bulk subphase. Desolvation of macromolecules followed by phase separation occurs on the surface. The initial rate of the phase separation of the solution is rather high, while the time dependence of the diameter of the spreading spot is described by a scaling law with an exponent almost equal to 2/3.

The combined superimposing influences of the surface area of silica nano-particles and molecular weight of polyethylene oxide matrix on the rheological properties of suspensions have been studied. The parameters of both components varied over a wide range: the surface area of silica from 100 to 390 m2/g, molecular weight of poly(ethylene oxide) from 200 to 2 × 105 Da, and concentration of silica from 1 to 13 vol%. In all cases, silica formed aggregates in suspension with apparent diameters of 50 to 230 nm; the higher values were observed for particles with larger surface area. Low-concentration suspensions in an oligomer matrix showed a slight non-Newtonian behavior; the size of silica particles was a determining parameter. Increasing the silica concentration led to dilatancy at high shear stresses. There was a threshold in the concentration dependence of viscosity, beyond which gelation of suspensions occurred. Depending on the silica concentration and molecular weight of the polymeric matrix, the dispersions behaved more like typical colloidal suspensions in a low molecular weight matrix or viscoelastic polymer melts containing an amount of solid filler. An increase in molecular weight of the polymeric matrix resulted in competition between increase in viscosity, appearance of viscoelasticity, and finally the transition from the gel state of a suspension in viscous medium to an elastic fluid.

Morphology and rheological properties of emulsions produced from heavy oil and aqueous solutions of surfactants with high hydrophilic-lipophilic balance (HLB) varying from 11 to 40 have been studied. The initial oil containing only trace amounts of water showed Newtonian properties over a wide temperature range (20–70 °C). As a function of preparing conditions, surfactant HLB and amount of aqueous solution, stable emulsions with different morphologies were formed: water/oil (W/O), double water 1 /oil/water 2 (W 1 /O/W 2 ) and oil 1 /water/oil 2 (O 1 /W/O 2 ), as well as multiple emulsions having more complicated morphology. Structural diversity of the emulsions determines the scatter of their rheological properties from Newtonian to visco-plastic. Introduction of aqueous solutions of surfactants with HLB ≥15 (Tween 80 and sodium dodecyl sulfate) gives rise to multiple emulsions characterized by a specific structure: ultradisperse W/O emulsion permeated with channels consisting of double W 1 /O/W 2 emulsions. Such multiple emulsions containing 15–25 vol% of surfactant aqueous solution exhibit non-Newtonian properties. Their effective viscosity at the shear rates typical for the oil flow regime in pipelines is reduced by 10–50 times as compared with the viscosity of the initial crude oil, being therefore acceptable for transportation.

The phase equilibrium and rheological properties of poly(1-trimethylsilyl-1-propyne) solutions obtained with tantalum catalysts are studied. For three polymers with different molecular masses, phase diagrams are determined in a number of solvents. From these diagrams, the Hansen solubility parameters of poly(1-trimethylsilyl-1-propyne) are calculated by the method proposed in this work. Dilute solutions of poly(1-trimethylsilyl-1-propyne) behave as Newtonian liquids, whereas the viscosity of viscoelastic concentrated systems decreases as the shear rate grows. The molecular and rheological characteristics of studied poly(1-trimethylsilyl-1-propyne) samples are compared with the samples prepared with NbCl5 catalysts. Poly(1-trimethylsilyl-1-propyne) obtained with a catalytic system involving tantalum pentachloride is characterized by high intrinsic viscosity and solution viscosity compared to poly(1-trimethylsilyl-1-propyne) prepared with niobium catalyst. The difference in properties is due to the dissimilar ratios of cis and trans units in the samples.