Study of Colloidal Stability and Viscosity of Concentrated Aqueous Silicasols

Проведено исследование коллоидной устойчивости наносуспензий, полученных разбавлением концентрированных силиказолей. Рассмотрен широкий диапазон массовых концентраций наночастиц (от 1 до 50 масс.%) и средних размеров первичных частиц (от 10 до 35 нм). Анализ седиментационных экспериментов показал, что рассмотренные образцы обладают очень высокой коллоидной устойчивостью. Проведена характеризация размеров наночастиц с помощью электронной микроскопии, получены распределения частиц по размерам в суспензии методом акустической спектроскопии. В результате было показано, что почти все рассматриваемые силиказоли имеют очень узкое распределение частиц по размеру. Получены зависимости динамической вязкости наносуспензий от концентрации и размера наночастиц. На их основе построены эмпирические корреляции в широком диапазоне концентраций частицA study of the colloidal stability of nanosuspensions obtained by diluting concentrated silicasols was carried out. A wide range of mass concentrations of nanoparticles (from 1 to 50 wt.%) and average sizes of primary particles (from 10 to 35 nm) were considered. The analysis of sedimentation experiments showed that the considered samples have a very high colloidal stability. The characterization of the nanoparticle sizes by electron microscopy was carried out. The particle size distributions in the suspension were obtained by acoustic spectroscopy. Almost all of the considered silica sols have been shown to have a very narrow particle size distribution. The dependences of the dynamic viscosity of nanosuspensions on the concentration and size of nanoparticles are obtained. Based on the dependences, empirical correlations in a wide range of particle concentrations were obtaine

Physicochemical properties of chitin isolated from shell of industrial crabs of various species

Differential thermal analysis was carried out over the range of –190 ÷ 400 °С on six samples of chitin from shells of industrial crabs of various species. All samples of the chitin have several relaxation transitions of endothermal character (g1-, g2-, β- and γ-)

Reactivity and Chemical Sintering of Carey Lea Silver Nanoparticles

Carey Lea silver hydrosol is a rare example of very concentrated colloidal solutions produced with citrate as only protective ligands, and prospective for a wide range of applications, whose properties have been insufficiently studied up to now. Herein, the reactivity of the immobilized silver nanoparticles toward oxidation, sulfidation, and sintering upon their interaction with hydrogen peroxide, sulfide ions, and chlorocomplexes of Au(III), Pd(II), and Pt(IV) was investigated using SEM and X-ray photoelectron spectroscopy (XPS). The reactions decreased the number of carboxylic groups of the citrate-derived capping and promoted coalescence of 7 nm Ag NPs into about 40 nm ones, excluding the interaction with hydrogen peroxide. The increased nanoparticles form loose submicrometer aggregates in the case of sulfide treatment, raspberry-like micrometer porous particles in the media containing Pd(II) chloride, and densely sintered particles in the reaction with inert H2PtCl6 complexes, probably via the formation of surface Ag-Pt alloys. The exposure of Ag NPs to HAuCl4 solution produced compact Ag films along with nanocrystals of Au metal and minor Ag and AgCl. The results are promising for chemical ambient temperature sintering and rendering silver-based nanomaterials, for example, for flexible electronics, catalysis, and other applications

Синтез опалов из частиц полиметилметакрилата в дисперсионных средах с различной вязкостью

The article was prepared based on the materials of the report at the first All-Russian scientific conference with international participation "YENISEI PHOTONICS – 2020". Photonic crystals are structures that have a spatial architecture with a periodically changing complex dielectric function at scales comparable to the wavelengths of light in the visible frequency range. The purpose of this study is to obtain three-dimensional photonic crystals by self-assembly from submicron spherical monodisperse particles of polymethylmethacrylate in dispersion media with different viscositiesФотонные кристаллы — это структуры, которые имеют пространственную архитектуру с периодически изменяющейся сложной диэлектрической функцией в масштабах, сопоставимых с длинами волн света в видимом диапазоне частот. Целью данной работы является получение трёхмерных фотонных кристаллов путём самосборки из субмикронных сферических монодисперсных частиц полиметилметакрилата в дисперсных средах с различной вязкость

Тепловые и механические свойства биокомпозита на основе поли-3-гидроксибутирата и бионаполнителя

Biodegradable poly-3-hydroxybutyrate [P(3HB)] and birch wood flour (as filler) were used to prepare powdered blends and then pellets and granules. Pellets were produced by cold pressing of polymer and filler powders; granules were produced from the powders wetted with ethanol. The properties of the initial P(3HB) and filler and the blends thereof were studied using IR spectroscopy, differential scanning calorimetry, X-ray analysis, and electron microscopy. No chemical bonds between the components were revealed; the blends were physical mixtures. The degree of crystallinity of the blends was lower than that of the initial polymer, suggesting different crystallization kinetics of the blends. The introduction of increasing amounts of filler into the polymer progressively decreased the mechanical strength of the pellets, as confirmed by a decrease in Young’s modulus. The resulting composite, based on biodegradable polymers and wood flour, is a promising nontoxic material for the production of wood-based panels for the construction industry and the manufacture of furniture in place of materials produced using toxic polyester resinsБиоразлагаемый поли-3-гидроксибутират [P(3HB)] и березовые опилки (в качестве наполнителя) использованы для приготовления порошкообразных смесей с целью получения форм в виде гранул и таблеток. Таблетки получены прямым холодным прессованием порошков полимера и наполнителя, гранулы – техникой гранулирования из пасты смеси полимера с опилками, увлажненной этанолом. Свойства исходного полимера, наполнителя и полученных смесей изучены с помощью ИК-спектроскопии, дифференциальной сканирующей калориметрии, рентгенографии и электронной микроскопии. Химических связей между компонентами обнаружено не было, следовательно, эти смеси представляют собой физические смеси. Степень кристалличности смесей была ниже, чем у исходного полимера, что свидетельствует о различной кинетике кристаллизации смесей. Увеличение содержания наполнителя в полимере снижало механическую прочность. Полученный на основе биоразлагаемого полимера и опилок композит имеет перспективу в качестве нетоксичного материала для производства древесных плит для стройиндустрии и мебельной промышленности вместо материалов, изготовленных с использованием токсичных полиэфирных смо

Biodegradable Polyhydroxyalkanoates Formed by 3- and 4-Hydroxybutyrate Monomers to Produce Nanomembranes Suitable for Drug Delivery and Cell Culture

Biodegradable polyhydroxyalkanoates, biopolymers of microbiological origin, formed by 3- and 4-hydroxybutyrate monomers P(3HB-co-4HB), were used to obtain nanomembranes loaded with drugs as cell carriers by electrospinning. Resorbable non-woven membranes from P(3HB-co-4HB) loaded with ceftazidime, doripinem, and actovegin have been obtained. The loading of membranes with drugs differently affected the size of fibers and the structure of membranes, and in all cases increased the hydrophilicity of the surface. The release of drugs in vitro was gradual, which corresponded to the Higuchi and Korsmeyer-Peppas models. Antibiotic-loaded membranes showed antibacterial activity against S. aureus and E. coli, in which growth inhibition zones were 41.7 ± 1.1 and 38.6 ± 1.7 mm for ceftazidime and doripinem, respectively. The study of the biological activity of membranes in the NIH 3T3 mouse fibroblast culture based on the results of DAPI and FITC staining of cells, as well as the MTT test, did not reveal a negative effect despite the presence of antibiotics in them. Samples containing actovegin exhibit a stimulating effect on fibroblasts. Biodegradable polyhydroxyalkanoates formed by 3-hydroxybutyrate and 4-hydroxybutyrate monomers provide electrospinning non-woven membranes suitable for long-term delivery of drugs and cultivation of eukaryotic cells, and are promising for the treatment of wound defects complicated by infection

Laser Processing of Polymer Films Fabricated from PHAs Differing in Their Monomer Composition

The study reports results of using a CO2-laser in continuous wave (3 W; 2 m/s) and quasi-pulsed (13.5 W; 1 m/s) modes to treat films prepared by solvent casting technique from four types of polyhydroxyalkanoates (PHAs), namely poly-3-hydroxybutyrate and three copolymers of 3-hydroxybutyrate: with 4-hydroxybutyrate, 3-hydroxyvalerate, and 3-hydroxyhexanoate (each second monomer constituting about 30 mol.%). The PHAs differed in their thermal and molecular weight properties and degree of crystallinity. Pristine films differed in porosity, hydrophilicity, and roughness parameters. The two modes of laser treatment altered these parameters and biocompatibility in diverse ways. Films of P(3HB) had water contact angle and surface energy of 92° and 30.8 mN/m, respectively, and average roughness of 144 nm. The water contact angle of copolymer films decreased to 80–56° and surface energy and roughness increased to 41–57 mN/m and 172–290 nm, respectively. Treatment in either mode resulted in different modifications of the films, depending on their composition and irradiation mode. Laser-treated P(3HB) films exhibited a decrease in water contact angle, which was more considerable after the treatment in the quasi-pulsed mode. Roughness parameters were changed by the treatment in both modes. Continuous wave line-by-line irradiation caused formation of sintered grooves on the film surface, which exhibited some change in water contact angle (76–80°) and reduced roughness parameters (to 40–45 mN/m) for most films. Treatment in the quasi-pulsed raster mode resulted in the formation of pits with no pronounced sintered regions on the film surface, a more considerably decreased water contact angle (to 67–76°), and increased roughness of most specimens. Colorimetric assay for assessing cell metabolic activity (MTT) in NIH 3T3 mouse fibroblast culture showed that the number of fibroblasts on the films treated in the continuous wave mode was somewhat lower; treatment in quasi-pulsed radiation mode caused an increase in the number of viable cells by a factor of 1.26 to 1.76, depending on PHA composition. This is an important result, offering an opportunity of targeted surface modification of PHA products aimed at preventing or facilitating cell attachment

Production and Properties of Microbial Polyhydroxyalkanoates Synthesized from Hydrolysates of Jerusalem Artichoke Tubers and Vegetative Biomass

One of the major challenges in PHA biotechnology is optimization of biotechnological processes of the entire synthesis, mainly by using new inexpensive carbon substrates. A promising substrate for PHA synthesis may be the sugars extracted from the Jerusalem artichoke. In the present study, hydrolysates of Jerusalem artichoke (JA) tubers and vegetative biomass were produced and used as carbon substrate for PHA synthesis. The hydrolysis procedure (the combination of aqueous extraction and acid hydrolysis, process temperature and duration) influenced the content of reducing substances (RS), monosaccharide contents, and the fructose/glucose ratio. All types of hydrolysates tested as substrates for cultivation of three strains—C. necator B-10646 and R. eutropha B 5786 and B 8562—were suitable for PHA synthesis, producing different biomass concentrations and polymer contents. The most productive process, conducted in 12-L fermenters, was achieved on hydrolysates of JA tubers (X = 66.9 g/L, 82% PHA) and vegetative biomass (55.1 g/L and 62% PHA) produced by aqueous extraction of sugars at 80 °C followed by acid hydrolysis at 60 °C, using the most productive strain, C. necator B-10646. The effects of JA hydrolysates on physicochemical properties of PHAs were studied for the first time. P(3HB) specimens synthesized from the JA hydrolysates, regardless of the source (tubers or vegetative biomass), hydrolysis conditions, and PHA producing strain employed, exhibited the 100–120 °C difference between the Tmelt and Tdegr, prevailing of the crystalline phase over the amorphous one (Cx between 69 and 75%), and variations in weight average molecular weight (409–480) kDa. Supplementation of the culture medium of C. necator B-10646 grown on JA hydrolysates with potassium valerate and ε-caprolactone resulted in the synthesis of P(3HB-co-3HV) and P(3HB-co-4HB) copolymers that had decreased degrees of crystallinity and molecular weights, which influenced the porosity and surface roughness of polymer films prepared from them. The study shows that JA hydrolysates used as carbon source enabled productive synthesis of PHAs, comparable to synthesis from pure sugars. The next step is to scale up PHA synthesis from JA hydrolysates and conduct the feasibility study. The present study contributes to the solution of the critical problem of PHA biotechnology—finding widely available and inexpensive substrates