Dependences of changes in the structural viscosity of oil films on the friction surface with fullerene compositions

In this work, the physical phenomenon of the formation of an oil film containing fullerenes was further developed, on the friction surface of tribosystems, which, in contrast to the known ones, takes into account the structural viscosity and structure of the formed film under the action of the electrostatic field of the friction surface. An increase in load significantly increases the structural viscosity of the gel structure, 13 - 20 times. The concentration of fullerenes in the base lubricant does not significantly affect the dynamic viscosity of aggregates in the composition of the liquid and the structure of the gel. An increase in the tribological properties of the base lubricant medium reduces the value of the structural viscosity of the gel on the friction surface by a factor of 3. At the same time, the concentration of fullerenes in the range of 0.5 - 1.5% does not have a large effect on these indicators. This phenomenon can be explained by the presence or absence of an additive package in the base lubricating medium. For those oils where the additive package is absent or present in a small amount J/m3, the introduction of a fullerene composition promotes the formation of clusters and micelles, which increase the structural viscosity and, consequently, form a film on the friction surface in the form of a gel structure. Conversely, if fullerenes are introduced into a base oil that contains a large and balanced additive package, where tribological properties are high J/m3, interaction at the molecular level does not occur. Fullerenes to a lesser extent will form stable aggregates in the form of micelles. The effect of reducing the coefficient of friction, equal to 96 %, is typical for low and medium loads of operation of tribosystems and base lubricants with average values of tribological properties. With increasing loads or tribological properties of base oils, the effect of the use of fullerenes decreases.

Investigation of the structural viscosity of oil films on the friction surface with fullerene compositions

The paper presents theoretical studies of changes in the structural viscosity of oil films on the friction surface with fullerene compositions in the field of action of electrostatic forces of the friction surface and the base lubricant. A feature of the use of fullerene additives in lubricants is that fullerenes are readily soluble in a wide class of organic and inorganic solvents. At the same time, poor solubility of fullerenes in technical oils (mineral, semi-synthetic and synthetic). The purpose of this work is to carry out theoretical studies of changes in the structural viscosity of oil films on the friction surface with fullerene compositions in the field of action of electrostatic forces of the friction surface and the base lubricant. On the basis of the working hypothesis, it was theoretically established that for a thin oil film, located in the field of action of electrostatic forces of the friction surface, it is necessary to consider the structural dynamic viscosity of the lubricant, which at the friction surface has a gel structure, and as the electrostatic forces from the friction surface decrease, the gel structure transforms into the sol structure. It is shown that the value of the structural viscosity of the considered aggregates is comparable with the viscosity of polymers or bitumen. Moreover, the viscosity of the gel structure is four orders of magnitude higher than the viscosity of the sol structure. An increase in the concentration of fullerenes leads to an increase in the dynamic viscosity of aggregates. It is theoretically shown that the structure of the oil film, which corresponds to the structure of the gel, belongs to the class of non-Newtonian fluids. With an increase in the sliding speed, the dynamic viscosity of such structures decreases by a factor of 4, which explains the destruction of micelle clusters and the appearance of rotational motions of elastic flocks. It is assumed that this will lead to a decrease in the value of the coefficient of friction. It is shown that for the gel structure, the concentration of fullerenes in the bulk of the base lubricant does not have a large effect on the structural viscosity. Conversely, for the structure of a sol, the concentration of fullerenes has a significant effect on the value of the structural dynamic viscosity.

Functional Method of Designing Self-Compacting Concrete

The article presents a new functional method of designing self-compacting concrete (SCC). The assumptions of the functional method of designing self-compacting concrete were based on the double coating assumption (i.e., it was assumed that the grains of coarse aggregate were coated with a layer of cement mortar, whereas the grains of sand with cement paste). The proposed method is composed of four stages, each of which is responsible for the selection of a different component of the concrete mix. The proposed designing procedure takes into consideration such a selection of the mineral skeleton in terms of the volumetric saturation of the mineral skeleton, which prevents the blocking of aggregate grains, and the designed liquid phase demonstrated high structural viscosity and low yield stress. The performed experimental studies, the simulation of the elaborated mathematical model fully allowed for the verification of the theoretical assumptions that are the basis for the development of the method of designing self-compacting concrete.

The Influence of pH Values on the Rheological, Textural and Release Properties of Carbomer Polacril® 40P-Based Dental Gel Formulation with Plant-Derived and Synthetic Active Components

The physicochemical properties, especially pH value of dental medicines, have significant influence on the health of oral cavity tissues. The pH of formulations should correspond to the value of saliva pH (5.5–8.0). For carbomer-based gels, the required pH value is obtained by neutralizing them with alkaline components, which leads to their structuring (thickening). This affects the physical properties of the gel, its residence time at the application site and the rate of release of active pharmaceutical ingredient. Therefore, the main purpose of this study is to evaluate the rheological, textural, and biopharmaceutical properties of Carbomer Polacril® 40P-based dental gel depending on the pH value. Evaluation of the rheological properties of gel preparations were performed by measuring the structural viscosity of the samples as a function of pH and temperature. The textural properties of the gel were evaluated by performing tests regarding back extrusion and spreadability. Carbomer Polacril® 40P-based gels haven’t shown noticeable thixotropic behavior, and were characterized by plastic flow in the whole studied pH range. The structural viscosity at the selected average pH value hasn’t differed at storage (25 °C) and application (37 °C) temperature. Texture studies of dental gels have shown a strong correlation with rheoparameters. Their rheological behavior and textural properties haven’t changed significantly between the pH range of 5.5–6.6. The relatively narrow range of working pH values does not affect the change in the viscosity of the preparation significantly and, consequently, does not affect the release of APIs from the developed Carbomer Polacril® 40P-based dental gel.

Development of the gel-mask composition with nettle juice intended for telogen effluvium cutaneous application

Taking into account the frequency of telogen effluvium in women, pharmaceutical market demand, a wide range of pharmacological effects of plant biologically active substances, it is important to develop a new medicinal cosmetic remedy in the form of a gel-mask with nettle juice. The aim of the work – the gel-mask composition development by the results of rheological, biological, microbiological and microscopic studies. The objects of the experiment were gel-mask model specimens with different ratios of nettle juice and auxiliary substances, gel base samples in combination with essential oils and different content of solubilizer PEG-40 hydrogenated castor oil (PEG-40 hсo). The structural viscosity was determined on a brookfield-type viscometer at a temperature of 20 ºc and a spindle speed of 20 rpm. The nettle juice optimal concentration was substantiated on a paramecium caudatum biological model with studying of gel-mask antioxidant properties. effectiveness confirmation of 0.1% potassium sorbate preservative was carried out using the method of the Ukraine state pharmacopoeia 2.0 (USP 2.0), paragraph 5.1.3. The influence of the peg-40 hсo concentration on the essential oil dispersion degree was studied with microscopic method. Considering influence of the auxiliary substances and nettle juice concentration on the gel-mask structural viscosity, the ingredients’ correlations were selected which reached the required viscosity limit for gels (2 000–10 000 mpa∙s), namely: carbopol ultrez 10 and sodium alginate by 0.5 %, potassium sorbate – 0.1 %, nettle juice – 10–20 the optimal concentration of nettle juice was 15%. It was justified by the results of the study of the antioxidant properties of the experimental samples on paramecium caudatum infusoria. The conducted microbiological studies confirmed the effectiveness of the application of 0.1% potassium sorbate preservative, which meets the requirements of criterion a for the USP 2.0. The influence of solubilizer peg-40 hco on the degree of mixture of essential oils dispersion when distributed on a gel basis was studied. it was confirmed that the optimal concentration of PEG-40 hco is 0.4%, namely the ratio 1:1 according to the content of the perfume. According to the complex experimental researches, the optimal composition of the gel-mask with nettle juice intended for telogen effluvium cutaneous application has been worked out.

Rheological Behaviors of Graphene Oxide/Polyacrylonitrile Spinning Solutions

The rheological behaviors of polyacrylonitrile (PAN) in NaSCN aqueous solutions containing different amount of Graphene oxide (GO) were investigated through both steady-state and dynamic rheological measurements. The parameters such as apparent viscosity (ηα), flow activation energy (Eη), structural viscosity index (Δη), storage modulus (G’), loss modulus (G’’) and mechanical loss factor (tanδ) were measured to illustrate the rheological behaviors of these solutions. The results showed that the apparent viscosity decreased with adding appropriate amount of GO, while the structural viscosity index, the flow activation energy and the mechanical loss factor of GO/PAN spinning solutions increased. Accordingly, a possible mechanism of GO effect on rheological behaviors of PAN solution was proposed in this work.