DIRECTED REGULATION OF THE STRUCTURAL AND RHEOLOGICAL PROPERTIES OF HEAT-INSULATING ACRYLIC AQUEOUS DISPERSIONS USING THE COMBINED USE OF HYDROPHILIC AND HYDROPHOBIC SILICATE FILLERS

The formation technology and performance characteristics of coatings based on aqueous dispersions are largely determined by the properties of the initial film-forming materials, which should ensure uniform thin-layer distribution on the substrate surface and the formation of coatings with the required technological complex of properties. Among them, due to their functional properties and relatively low cost, the most widespread are water-dispersion polymer coatings based on acrylic film-formers. In this paper, mathematical models of the structural and rheological dependences of heat-insulating acrylic aqueous dispersions are considered depending on the combined content of hydrophilic-hydrophobic fillers. To describe these dependencies, it is advisable to use equations of the second degree. According to the mathematical theory of experiment, the second-order orthogonal central compositional design makes it possible to predict the behavior of the response function. Carrying out an experiment in accordance with this plan makes it possible to establish the analytical dependence of the response function on the corresponding factors in the form of a polynomial equation of the second degree. The main response functions were: conditionally static yield stress, viscosity at the minimum rate of onset of fracture (initial effective viscosity), viscosity of the “destroyed” structure according to the Newtonian nature of the flow, activation energy of viscous flow at minimum, average and maximum shear rates. On the basis of the established dependences, the optimal ratios of hydrophobized aerosil and aluminosilicate microspheres were selected, the combined use of which makes it possible to reduce shear stresses to create a homogeneous aqueous acrylic dispersion, to predict the activation energy at various technological stages of preparation and application of heat-insulating coatings. The established results made it possible to create a hydrophilic-hydrophobic aqueous acrylic dispersion, which, without the use of surfactants, makes it possible to simplify the production technology of heat-insulating water-dispersion coatings, namely, to exclude the stage of pretreatment of fillers, to reduce the rotation speed of the frame mixer, and also to increase the kinetic stability of the finished dispersion.

Rheological and thermal stability of interpenetrating polymer network hydrogel based on polyacrylamide/hydroxypropyl guar reinforced with graphene oxide for application in oil recovery

The purpose of the present work is to enhance the thermal stability and rheological properties of semi-interpenetrating polymer network (IPN) hydrogel based on partially hydrolyzed polyacrylamide/hydroxypropyl guar (HPAM/HPG) nanocomposite reinforced with graphene oxide (GO), at temperatures (200 and 240 °F) for use in oil recovery applications. FTIR spectra of the IPN nanocomposite hydrogels revealed interactions of GO with HPAM/HPG chains. An increase in the viscosity is also observed from the rheological study. Moreover, IPN and its nanocomposite hydrogels exhibited non-Newtonian behavior. The decline of viscosity of IPN nanocomposite hydrogels was observed with an increase in the temperature from 200 to 240 °F but was still higher than IPN hydrogel without GO. Dispersion of GO through the HPAM/HPG hydrogel matrix was evaluated by SEM morphology and electrical conductivity. The IPN nanocomposite hydrogels showed high viscosity stability, thermal stability, and flow activation energy as compared to IPN hydrogel without GO. Therefore, the addition of 0.1 wt.% of GO to the HPAM/HPG matrix is suitable to create a cross-linked polymer solution with improved properties which may be beneficial for use in oil recovery applications.

Effect of MgO and K2O on High-Al Silicon–Manganese Alloy Slag Viscosity and Structure

The viscosity, melting proprieties, and molten structure of the high-Al silicon–manganese slag of SiO2–CaO–25 mass% Al2O3–MgO–MnO–K2O system with a varying MgO and K2O content were studied. The results show that with the increase in MgO content from 4 to 10 mass%, the measured viscosity and flow activation energy decreases, but K2O has an effect on increasing those of slags. However, the melting temperature increases due to the formation of high-melting-point phase spinel. Meanwhile, Fourier transform infrared (FTIR) and X-ray photoelectron spectra (XPS) were conducted to understand the variation of slag structure. The O2− dissociates from MgO can interact with the O0 within Si–O or Al–O network structures, corresponding to the decrease in the trough depth of [SiO4] tetrahedral and [AlO4] tetrahedral. However, when K2O is added into the molten slag, the K+ can accelerate the formation of [AlO4] tetrahedra, resulting in the increase in O0 and O− and the polymerization of the structure.

Connecting the stimuli-responsive rheology of biopolymer hydrogels to underlying hydrogen-bonding interactions

Many biopolymer hydrogels are environmentally responsive because they are held together by physical associations that depend on pH and temperature. Here we investigate how the pH and temperature response of the rheology of hyaluronan hydrogels is connected to the underlying molecular interactions. Hyaluronan is an essential structural biopolymer in the human body with many applications in biomedicine. Using two-dimensional infrared (2DIR) spectroscopy, we show that hyaluronan chains become connected by hydrogen bonds when the pH is changed from 7.0 to 2.5, and that the bond density at pH 2.5 is independent of temperature. Temperature-dependent rheology measurements show that due to this hydrogen bonding the stress relaxation at pH 2.5 is strongly slowed down in comparison to pH 7.0, consistent with the sticky reptation model of associative polymers. From the flow activation energy we conclude that each polymer is crosslinked by multiple (5-15) hydrogen bonds to others, causing slow macroscopic stress relaxation, despite the short time scale of breaking and reformation of each individual hydrogen bond. Our findings can aid the design of stimuli-responsive hydrogels with tailored viscoelastic properties for biomedical applications.

Effect of Solid Additives on the Rheological Property of Nitroglycerin Plasticized Nitrocellulose

The rheological properties of energetic materials comprising nitroglycerin plasticized nitrocellulose were studied using rheological tests in a parallel plate rheometer. The Carreau-Yasuda equation was applied to calculate the zero-shear viscosity, and the dependence of solid additives, temperature and solvent content on zero-shear viscosity was developed. One can study flow characteristics of the energetic materials by observing the zero-shear viscosity instead of the effect of solid additives, temperature and solvent content. Additionally, the relationship between zero-shear viscosity and additives concentration was studied. The Kissinger-Akahira-Sunose (KAS) method was used to obtain the viscous flow activation energy, and the equation to describe the relationship between solid additives concentration and viscous flow activation energy was represented. The Zero-Shear Viscosity (ZSV) test showed that temperature was the predominant effect on the ZSV value at low solvent content, as the concentration of solid additives increased, the ZSV value decreased at low solvent content but increased at high one, however, there is an opposite trend when graphene concentration is above 0.1%. The viscous flow activation energy showed different changing trends with solid concentration that increased at different solvent content. The master curves were obtained by Time-Temperature Equivalence Principle, the viscosity prediction model has been established and showed a good agreement with the experimental data, compared with the test results, the viscosity prediction model is more accurate at low temperature (15°C-25°C). The obtained knowledge of the different equations will form a contribution to the research on extrusion process of this energetic material containing Cyclotrimethylenetrinitramine (RDX) and graphene, and the results obtained by this research have certain practical significance of the extrusion process for this energetic material.

DEPENDENCE OF DYNAMIC VISCOSITY OF NAPHTHENIC HYDROCARBONS IN CYCLOPENTANE SERIES ON QUANTUM AND STRUCTURAL PARAMETERS

Interrelation of parameters for Newtonian fluid viscous flow of monocyclic hydrocarbons with quantum and structural (topological) characteristics of molecules are considered. Ionization potentials and topological indices, respectively, were considered as quantum and topological characteristics. The vertical ionization potentials were calculated by the Koopmans ' theorem of quantum chemical methods with full molecular geometry optimization. We have studied topological indices that take into account the size and shape of the molecular graph. As a topological descriptors the Wiener index, the Balaban centric index, the Randic index (the index of molecular connectivity), Gutman (Szeged) index, Platt index and the Harary index were considered. For hydrocarbons in cyclopentane series with side chains, the kinetic compensation effect of dynamic viscosity has been established, which connects the activation energy and Arrhenius factor in the framework of the Frenkel-Eyring model. It is established that for compounds of a number of five-membered naphthenes, the apparent activation energy for viscous flow and the associated pre-exponential factor, depends on quantum parameters (ionization potentials) and the topology of the molecules. In this paper, a regression quantitative structure−property relationship (QSPR) is proposed using as descriptors the ionization potentials and topological indices for the prediction of dynamic viscosity. Prognostics capabilities of the proposed model and the adequacy of the forecast were verified by calculating the values of the dynamic viscosity of hydrocarbons that are not included in the base series. Experimental and theoretical substantiation of the proposed regularity was given within the framework of the representation of the viscous flow activation energy as a measure of intermolecular interaction and the predominance of dispersion interaction in hydrocarbon molecules for cyclopentane series. The equation obtained during the study can be used to predict the viscosity characteristics of synthesized and natural five-membered naphthenes.

Effects of B2O3 on Melting Characteristics and Temperature-Dependent Viscosity of High-Basicity CaO–SiO2–FeOx–MgO Slag

In order to reduce the amount of fluorite during the steelmaking process for environmental protection, it is essential to investigate the fluorine-free slag system. Thus, high-basicity CaO–SiO2–FeOx–MgO slag with B2O3 content from 0% to 15% was designed, and its melting characteristics and viscosity were investigated. The influence of B2O3 content on the phase diagram of the slag system was calculated using FactSage 7.3, and the break temperature was determined from the curves of temperature-dependent viscosity. The results show that, with the increase in B2O3 content, the melting characteristics of the CaO–SiO2–FeOx–MgO/B2O3 slag system, including liquidus temperature, flow temperature, softening temperature, and hemispheric temperature, all decreased; the main phase of the slag system transformed from Ca2SiO4 into borosilicate, and finally into borate; the viscous flow activation energy reduced from 690 kJ to 130 kJ; the break temperature reduced from 1590 °C to 1160 °C. Furthermore, the melting characteristics and the break temperature of the slag system with 5% and 8% B2O3 content were found to be the closest to the values of fluorine-containing steel slag.

Cross-Linker Control of Vitrimer Flow

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

Cross-Linker Control of Vitrimer Flow

<div><p>Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that cross-linker reactivity represents an additional design parameter to tune stress relaxation rates in vitrimers. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition—elimination of thiols in a PDMS vitrimer. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.</p></div>

Cross-Linker Control of Vitrimer Flow

Vitrimers are a class of covalent adaptable networks (CANs) that undergo topology reconfiguration via associative exchange reactions, enabling reprocessing at elevated temperatures. Here, we show that the use of an associative mechanism additionally enables decoupling of stiffness and stress relaxation. Guided by calculated activation barriers, we prepared a series of cross-linkers with varying reactivity for the conjugate addition–elimination of thiols in a PDMS vitrimer, and demonstrate modulation of stress relaxation rate while maintaining constant stiffness. Surprisingly, despite a wide range of stress relaxation rates, we observe that the flow activation energy of the bulk material is independent of the cross-linker structure. Superposition of storage and loss moduli from frequency sweeps can be performed for different cross-linkers, indicating the same exchange mechanism. We show that we can mix different cross-linkers in a single material in order to further modulate the stress relaxation behavior.