In this work, the deformation dynamics of viscoelastic droplets of polyacrylonitrile (PAN) solutions in dimethyl sulfoxide flowing in silicone oil through a channel with an abrupt contraction is investigated experimentally and by numerical simulation. The main attention is focused on the influence of PAN concentration and capillary number on the deformation behavior and stability of such droplets. It is shown that increasing PAN concentration leads to a substantial increase in droplet elongation. The mode of droplet instability development also depends on the polymer concentration: at low PAN contents, the primary droplet is disintegrated into secondary droplets of comparable sizes, whereas, at higher polymer concentrations, the formation of a “swallow-tail” structure is followed by its disintegration into small satellite droplets. The observed trends are systemized as droplet stability diagrams plotted in the capillary number–PAN concentration coordinates. The obtained results are of interest for the development of technologies for producing microfibers based on viscoelastic polymer solutions using flow focusing in microfluidic chips.

This study investigates the physicochemical and rheological properties of fuel oil released during the December 2024 spill in the Kerch Strait, aiming to elucidate its behavior under varying environmental conditions and the mechanisms of its transformation in marine sediments. Comprehensive rheological measurements were performed on samples collected from the damaged tanker and from the seafloor, within a temperature range of 0-50 °C. All tested oils exhibited a pronounced transition from Newtonian to yield-stress flow behavior as the temperature dropped below 20 °C, indicating the formation of a structured dispersion phase. The rheological response of coastal sediments contaminated with fuel oil was also examined; these systems behaved as viscoplastic media capable of sustaining significant irreversible deformation under low shear stress. Furthermore, the addition of the nonionic surfactant Tween 80 was found to induce the formation of a time-dependent oil-in-water emulsion with a viscosity reduced by more than an order of magnitude compared to the original fuel oil, thereby enhancing its potential for dispersal and biodegradation. The mechanical strength and cohesion of the surface fuel layer were quantified, revealing temperature-dependent consolidation processes. Overall, the results provide a quantitative framework for understanding the temperature- and composition-controlled rheology of marine fuel oil residues, offering insights for the optimization of remediation strategies in cold marine environments.

A new unique two-stage method for spinning hollow polynaphthoylenebenzimidazole (PNBI) fibers has been proposed. Polyacrylonitrile (PAN) fiber having a porous morphology was coated with poly(o-aminophenylene)- naphthoylenimide (PANI-O) precursor to form a composite fiber with a core–shell structure and subsequently this composite fiber precursor was heat treated in air. The inner PAN fiber underwent oxidative cyclization, accompanied by its high shrinkage, while the PANI-O shell, due to heterocyclization, turned into a PNBI-O shell, and the inner space of the hollow fiber was only partially filled with cyclized PAN.

The fiber formation process via the uniaxial stretching jet of concentrated polyacrylonitrile solutions in dimethyl sulfoxide has been investigated. Data on viscoelastic properties obtained by oscillatory shear rheometry have been compared with the evolution of jet thinning during stretching. It was found that at a fixed temperature and moderate air humidity (20%), the jet thinning process involves an initial rapid viscous thinning followed by phase separation and the formation of solid fibers coated with solvent droplets. Changes in morphology as the solution transforms into solid fiber were analyzed using cryo-microscopy. It was demonstrated that at the final thinning stages there exists an increase in a solvent concentration in the near-surface layers of the jet/fiber. Finally, the role of air humidity was analyzed. Two possible scenarios of fiber formation were considered: predominantly due to uniaxial deformation or through coagulation of solution with moisture from the air humidity. Comparative morphological analysis of prepared fiber cross sections showed that monolithic fibers with homogeneous transverse morphology are obtained in the case of strain-induced formation. In contrast, fibers obtained due to phase separation induced by air humidity have gradient porosity. The mechanisms underlying the observed behavior are discussed.

This study focuses on the development of environmentally sustainable polypropylene (PP)-based composites with the potential for biodegradability by incorporating cellulose and the oligomeric siloxane ES-40. Targeting industrial applications such as fused deposition modeling (FDM) 3D printing, ES-40 was employed as a precursor for the in situ formation of silica particles via hydrolytic polycondensation (HPC). Two HPC approaches were investigated: a preliminary reaction in a mixture of cellulose, ethanol, and water, and a direct reaction within the molten PP matrix. The composites were thoroughly characterized using rotational rheometry, optical microscopy, differential scanning calorimetry, and dynamic mechanical analysis. Both methods resulted in composites with markedly reduced crystallinity and shrinkage compared to neat PP, with the lowest shrinkage observed in blends prepared directly in the extruder. The inclusion of cellulose not only enhances the environmental profile of these composites but also paves the way for the development of PP materials with improved biodegradability, highlighting the potential of this technique for fabricating more amorphous composites from crystalline or semi-crystalline polymers for enhancing the quality and dimensional stability of FDM-printed materials.

A series of linear high molecular weight acrylonitrile homopolymers have been synthesized using controlled anionic polymerization. The possibility of producing polyacrylonitrile with a wide range of molecular weights by controlling the concentrations of metal-free initiator and water has been demonstrated. The resulting homopolymers exhibit excellent spinnability.

The rheological properties, spinnability, and thermal–oxidative stabilization of high-molecular-weight linear polyacrylonitrile (PAN) homopolymers (molecular weights Mη = 90–500 kg/mol), synthesized via a novel metal-free anionic polymerization method, were investigated to reduce coagulant use, enable solvent recycling, and increase the carbon yield of the resulting carbon fibers. This approach enabled the application of the mechanotropic (non-coagulating) spinning method for homopolymer PAN solutions in a wide range of molecular weights and demonstrated the possibility of achieving a high degree of fiber orientation and reasonable mechanical properties. Rheological analysis revealed a significant increase in solution elasticity (G′) with increasing molecular weight, facilitating the choice of optimal deformation rates for effective chain stretching prior to strain-induced phase separation during the eco-friendly spinning of concentrated solutions without using coagulation baths. The possibility of collecting ~80 wt% of the solvent at the first stage of spinning from the as-spun fibers was shown. Transparent, defect-free fibers with a tensile strength of up to 800 MPa and elongation at break of about 20% were spun. Thermal treatment up to 1500 °C yielded carbon fibers with a carbon residue of ~50 wt%, in contrast to ~35 wt% for industrial radically polymerized PAN carbonized under the same conditions.

We studied the effect of water addition on the gelation kinetics of polyacrylonitrile (PAN) in dimethyl sulfoxide (DMSO) solutions. The gelation process was considered an evolution of the rheological properties, which were associated with a change in the PAN-DMSO-water system interactions. This approach enabled a detailed investigation of gelation kinetics and phase transformations across varying temperatures, identifying regions associated with solutions, dispersions, thermoreversible, and thermo-irreversible gels. The gelation temperatures of the ternary systems were ascertained using the Winter method. A pivotal element in the gelation process of PAN solutions was identified: the ratio of the unassociated solvent concentration available for PAN solvation relative to the PAN concentration. This specific ratio is instrumental in dictating the formation of nitrile-nitrile interactions. The obtained results will contribute to the understanding of physicochemical approaches to optimizing the composition of gelling polymer solutions in technologies, giving new knowledge to the fields of polymer and materials science.

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.

Terpolymers of acrylonitrile with acrylic acid and alkyl acrylates, including methyl-, butyl-, 2-ethylhexyl-, and lauryl acrylates, were synthesized using the reversible addition–fragmentation chain transfer method. In this study, the focus was on the investigation of the impact of different monomer addition methods (continuous and batch) on both the rheological behavior of the spinning solutions and the mechanical properties of the resulting fibers. Our findings revealed that the method of monomer addition, leading either to non-uniform copolymers or to a uniform distribution, significantly influences the rheological properties of the concentrated solutions, surpassing the influence of the alkyl-acrylate nature alone. To determine the optimal spinning regime, we examined the morphology and mechanical properties at different stages of fiber spinning, considering spin-bond and orientation drawings. The fiber properties were found to be influenced by both the nature and introducing method of the alkyl-acrylate comonomer. Remarkably, the copolymer with methyl acrylate demonstrates the maximum drawing ratios and fiber tensile strength, reaching 1 GPa. Moreover, we discovered that continuous monomer addition allows for reaching the higher drawing ratios and superior fiber strength compared to the batch method.

We investigated how different solvents' affinity with polyacrylonitrile affects the formation of a jet that leads to stable fiber spinning. The study focused on two concentrations, one near and one above the crossover point where the topological entanglements are formed in the semi-dilute solutions. The role of the physical parameters of the solutions, including solvent-polymer affinity, viscosity, surface tension, and relaxation times, was analyzed. The experiment involved the uniaxial deformation of a solution drop under its weight, observed using a high-speed microscopic camera. The stability of the jet was associated with the relaxation time and solventpolymer affinity. The continuous fiber spinning is mainly determined by the high enough polymer concentration in the solution, and the solvent nature, or by how the solution state is close to the theta conditions. Bicomponent mixed solvents offer two viable routes to achieve this - evaporating a more volatile component from the mixture to increase the polymer concentration, or modifying the solvent with a combination of solvents of different solvent quality. Both approaches have been experimentally validated, enabling the production of continuous stable fibers in the gel stretching regime. In this case, the jet stretching occurs under conditions Wi > 1. Thereby, the transition to the gel state promotes the necessary conditions for macromolecule orientation during fiber spinning.

This study presents preparing and characterization of polyacrylonitrile (PAN) fibers containing various content of tetraethoxysilane (TEOS) incorporated via mutual spinning solution or emulsion using wet and mechanotropic spinning methods. It was shown that the presence of TEOS in dopes does not affect their rheological properties. The coagulation kinetics of complex PAN solution was investigated by optical methods on the solution drop. It was shown that during the interdiffusion process phase separation occurs and TEOS droplets form and move in the middle of the dope’s drop. Mechanotropic spinning induces the TEOS droplets to move to the fiber periphery. The morphology and structure of the fibers obtained were investigated by scanning and transmission electron microscopy, as well as X-ray diffraction methods. It was shown that during fiber spinning stages the transformation of the TEOS drops into solid silica particles takes place as a result of hydrolytic polycondensation. This process can be characterized as the sol-gel synthesis. The formation of nano-sized (3–30 nm) silica particles proceeds without particles aggregation, but in a mode of the distribution gradient along the fiber cross-section leading to the accumulation of the silica particles either in the fiber center (wet spinning) or in the fiber periphery (mechanotropic spinning). The prepared composite fibers were carbonized and according to XRD analysis of carbon fibers, the clear peaks corresponding to SiC were observed. These findings indicate the useful role of TEOS as a precursor agent for both, silica in PAN fibers and silicon carbide in carbon fibers that has potential applications in some advanced materials with high thermal properties.

High strength flame-resistant semi-ladder fibers of the "Lola " family (PNBI) have been obtained by an acid-free and more environmentally friendly method with controlled heating of precursor fibers in an inert atmosphere. The suggested two-step method consists in preparation of a prepolymer (PANI-O) in N-methylpyrrolidone. The prepared PANI-O dopes were additionally modified by introducing a certain part of a non-solvent (ethanol) to smooth the interdiffusion mass-transfer and prepare defectless precursor fibers. A detailed study of the thermal behavior of the PANI-O fibers by DSC and TGA shows that the maximum exothermic effect is observed at 320-370 degrees C, associated with formation of a ladder structure, i.e., transformation of the PANI-O into the PNBI-O. As a result, after the heat treatment, the flame-resistant PNBI "Lola " family fibers were obtained with an oxygen index of up to 83, tensile strength of similar to 500 MPa, relative elongation of-5% and elastic modulus of similar to 12 GPa.

Controlled synthesis of terpolymers of acrylonitrile with acrylamide and alkyl acrylate of similar composition but differing in the alkyl substituent (methyl, butyl, 2-ethylhexyl, and lauryl) has been performed for the first time via the reversible addition-fragmentation chain transfer polymerization under the action of dibenzyl trithiocarbonate. Investigation of thermal behavior of the terpolymers under inert atmosphere has allowed determination of the activation energy of the ionic cyclization as of ~80 kJ/mol irrespectively of the alkyl acrylate nature. Mechanism of chemical transformations of the terpolymers under isothermal treatment at 250°C has not differed from this known for the binary acrylonitrile–acrylamide and acrylonitrile–alkyl acrylate copolymers. At the same time, the rate of the polyconjugated structure formation has been higher in comparison with the analogous terpolymers with acrylic acid. The rate of the stabilization has changed along the following series of alkyl acrylates: methyl acrylate < butyl acrylate ≈ 2-ethylhexyl acrylate < lauryl acrylate. Concentration ranges of the dilute, semidilute, and concentrated solutions have been determined for the synthesized terpolymers.

We examined the rheological properties of polyacrylonitrile (PAN) solutions in seven solvents over a wide range of shear rates. These solutions were characterized using the Hansen solubility parameter. The vis-cosity of these dilute solutions was primarily determined by this parameter. However, above the cross-over point (at c[g] > 0.7) not only viscosity but also nature of the solvents was found to be an important factor. At high polymer concentrations, certain solutions showed gelation tendency.This study aims to determine a correlation between the rheological properties of the solutions and the affinity of the solvent with PAN. These correlations are present for an intrinsic viscosity (or the Huggins constant), a second virial coefficient, and solubility parameter. However, in certain cases, experimental points do not correspond to general dependence. This is also observed for these solutions when present-ing the data of viscoelastic measurements in G0-G00 coordinates: certain points deviate from the general dependence.A detailed infrared spectroscopy analysis has been used for examining these experimental results. It has been shown the water presence in the solvents and polymer solutions even than anhydrous solvents were used. Water presence tend to a solvent-water associate formation in the solutions. The solubility of PAN in these solvents and the gelation tendency depends on the polymer concentration, in addition to the structure and stability of the polymer-water associates. The experimental results obtained and the reported correlation made it possible to develop a subsequence of solvents used as per their affinity with PAN. The charactristics of dilute solutions were compared with the rheological properties of moderately concentrated solution.(c) 2022 Elsevier B.V. All rights reserved.

Branched polyacrylonitrile has been synthesized via anionic polymerization with the 1,4-diazabicyclo[2.2.2]octane–ethylene oxide initiating system. The degree of branching has been determined by means of NMR spectroscopy and indirectly confirmed by viscometry of the dilute solutions. Solutions of binary mixtures of the branched PAN with the industrial linear polymer in dimethyl sulfoxide with different ratio of the components have been prepared; their rheological behavior has been investigated. It has been shown that the introduction of the branched polymer in a solution of linear PAN allows significant decrease in the mixed solutions viscosity at equal total fraction of the polymer. The addition of branched PAN in a solution of the linear PAN has increased the total concentration of the polymer in the system favoring the increase in the viscosity of the mixed solution, but the viscosity has been significantly lower than this of the equally concentrated solution of the linear polymer. Investigation of the frequency dependences of the components of complex shear modulus of these solutions has revealed that the increase in the viscoelastic properties is mainly due to the increase in the elasticity modulus. Exponent of the frequency dependence of the loss modulus in the terminal zone has not been changed, whereas this of the elasticity modulus has been decreased to 0.4 over the entire range of the ratio between the branched and linear PAN. The specific relaxation time has been decreased with the increase in the fraction of linear PAN. Thermal behavior of linear and branched PAN has been investigated by means of DSC. The performed study has revealed the possibility of preparation of the mixed films and fibers based on linear and branched polyacrylonitrile.

The fumed silica influence on the morphology, coagulation processes, and rheological properties of suspensions in dimethyl sulfoxide (DMSO) and polyacrylonitrile (PAN)–DMSO solutions has been studied for the production of composite films and fibers. It has been shown that silica–DMSO concentrated suspensions (24 wt%) form a weak gel with a yield point of about 200 Pa. At concentrations of ~5 wt% and above the dispersions, depending on the shear stress, are pseudoplastic or dilatant liquids. It has been found that the silica addition method into a PAN solution has a significant impact on the aggregates dispersibility and the rheological behavior of the obtained systems. A thixotropy appearance and a sharp increase in the relaxation time were observed for PAN solutions at a SiO2 content of more than 3−5 wt%, which indicates the formation of structures with a gel-like rheological behavior. Upon reaching the critical stress their destruction takes place and the system starts to behave like a viscoelastic liquid. Two spinning methods have been used for preparing fibers: standard wet and mechanotropic. By the mechanotropic method it is possible to achieve a higher draw ratio at spinning and to obtain fibers with better mechanical properties. It is possible to spin fibers from PAN solutions containing up to 15 wt% of silica per polymer with a tensile strength up to 600 MPa.

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.

Polyacrylonitrile terpolymers based on acrylonitrile, acrylic acid, and methyl acrylate were synthesized by reversible addition–fragmentation chain-transfer polymerization with varying the monomer addition sequence during the synthesis. The monomer introduction sequence in the synthesis of a ternary copolymer significantly affects both the rheological properties of solutions and the strength of obtained fibers.

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%.