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1
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Comparison of stability properties of poly(acrylic acid) adsorbed on the surface of silica, alumina and mixed silica-alumina nanoparticles - application of turbidimetry method

100%
Wiśniewska M., Urban T., Nosal-Wiercińska A., Zarko V., Gun’ko V.
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issue 4
476-479
EN
The influence of anionic poly(acrylic acid) - PAA addition on the stability of synthesized silica, alumina and mixed silica-alumina suspensions as a function of solution pH was studied. The turbidimetry method was used to monitor the changes of the examined systems stability over time. The calculated stability coefficients enabled estimation of polymer adsorption influence on stability of metal oxide suspension. It was shown that the alumina suspension without the polymer is the most unstable at the pH values 6 and 9, whereas the silica polymer was most unstable at pH 3. PAA with higher molecular weight (240 000) is a relatively effective stabilizer of all investigated adsorbents (except silica at pH 3). These properties of poly(acrylic acid) are highly desirable in many branches of industry (e.g. production of cosmetics, pharmaceuticals, paints) where polymers are widely used as effective stabilizers of colloidal suspensions.
2
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Interaction of fibrinogen with nanosilica

86%
Rugal A., Gun’ko V., Barvinchenko V., Turov V., Semeshkina T., Zarko V.
Open Chemistry
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2007
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vol. 5
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issue 1
32-54
EN
Interaction of human plasma fibrinogen (HPF) with fumed nanosilica A-300 in a phosphate buffer solution (PBS) was studied using 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water in the temperature range of 210–273 K, TSDC (90 T FTIR, and UV spectroscopy methods. An increase in concentration of HPF in the PBS leads to a decrease in amounts of structured water (frozen at T FTIR and UV spectra show that the HPF adsorption on silica leads to structural changes of the protein molecules. These changes and formation of hybrid HPF/A-300 aggregates can increase the rate of clotting that is of importance on nanosilica application as a component of tourniquet preparations. [...]
3
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Effects of dissolved metal chlorides on the behavior of silica nanoparticles in aqueous media

86%
Gun’ko V., Andriyko L., Zarko V., Marynin A., Olishevskyi V., Janusz W.
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issue 4
480-491
EN
Effects of chlorides of univalent (LiCl, NaCl, KCl), bivalent (MgCl2, BaCl2) and trivalent (AlCl3) metals at different concentration (0.001–0.1 M) on the behavior of nanosilica A-200 (0.5–5 wt.%) in aqueous media are analyzed using photon correlation spectroscopy (particle size distribution, PSD), electrophoresis (zeta potential ζ), potentiometric titration (surface charge density), and estimation of screening length of primary particles and their aggregates. The zeta potential and the PSD are affected by silica content, pH, and concentration and type of dissolved salts. Smaller but more strongly hydrated Li+ cations caused stronger nonlinear dependences of the zeta potential on pH and salt content than Na+ or K+. This nonlinearity is much stronger at a lower content of silica (0.5–1 wt.%) than at C A-200 = 2.5 or 5 wt.%. At a high concentration of nanosilica (5 wt.%) the effect of K+ ions causes stronger diminution of the negative value of the zeta potential due to better adsorption of larger cations. Therefore, the influence of K+ on increasing screening length is stronger than that of Na+ for both primary nanoparticles and their aggregates. A similar difference in the ζ values is observed for different in size cations Ba2+ and Mg2+.
4
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Effect of solution pH on the stability of mixed silica -alumina suspension in the presence of polyacrylic acid (PAA) with different molecular weights

86%
Wiśniewska M., Terpiłowski K., Chibowski S., Urban T., Zarko V., Gun’ko V.
Open Chemistry
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2013
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vol. 11
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issue 1
101-110
EN
The influence of solution pH (in the range 3–9) on mixed silica-alumina suspension in the absence and presence of polyacrylic acid (PAA) was studied. The composition of the adsorbent was SiO2 (97%) and Al2O3 (3%). The turbidimetry method was applied to record changes in the stability of the investigated systems as a function of time. It was shown that the suspension without the polymer is less stable at pH 3, whereas at pH 6 and 9, the systems were stable. PAA with molecular weights 100 000 and 240 000 at pH 3 (improvement of system stability conditions) and PAA 2 000 at pH 6 (deterioration of suspension stability) have a great effect on the silica-alumina suspension stability. The stabilization-flocculation properties of polyacrylic acid are a result of a specific conformation of its chains on the solid surface where it depends on the solution pH and the polymer molecular weight.
5
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Behaviour of pure water and water mixture with benzene or chloroform adsorbed onto ordered mesoporous silicas

73%
Gun’ko V., Turov V., Turov A., Zarko V., Gerda V., Yanishpolskii V., Berezovska I., Tertykh V.
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EN
Structural characteristics of synthesized ordered mesoporous silicas MCM-41, MCM-48 and SBA-15 were studied using XRD, nitrogen adsorption and FTIR methods. Pure water and mixtures with water/benzene and water/chloroform-d adsorbed onto silicas were studied by 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial liquids. Concentrated aqueous suspensions of MCM-48 and SBA-15 were studied by thermally stimulated depolarization current (TSDC) method. Benzene and chloroform-d can displace a portion of water to broad pores from the pore walls and from narrower pores, especially in the case of a large excess of an organic solvent. This process is accompanied by diminution of both interaction energy of water with an adsorbent surface and freezing temperature depression of adsorbed water. The effect of nonpolar benzene on pore water is much stronger than that of weakly polar chloroform-d. Modifications of the Gibbs-Thomson relation to describe the freezing point depression of mixtures of immiscible liquids confined in pores allow us to determine distribution functions of sizes of structures with unfrozen pore water and benzene. [...]
6
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Interaction of unmodified and partially silylated nanosilica with red blood cells

73%
Gun’ko V., Galagan N., Grytsenko I., Zarko V., Oranska O., Osaulenko V., Bogatyrev V., Turov V.
Open Chemistry
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2007
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vol. 5
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issue 4
951-969
EN
Interaction of red blood cells (RBCs) with unmodified and partially (50%) silylated fumed silica A-300 (nanosilica)was studied by microscopic, XRD and thermally stimulated depolarisation current (TSDC) methods. Nanosilica at a low concentration C A-300C A-300 = 1 wt% all RBCs transform into shadow corpuscles because of 100% haemolysis. Partial (one-half) hydrophobization of nanosilica leads to reduction of the haemolytic effect in comparison with unmodified silica at the same concentrations. A certain portion of the TSDC spectra of the buffered suspensions with RBC/A-300 is independent of the amounts of silica. However, significant portions of the low-and high-temperature TSDC bands have a lower intensity at C A-300 = 1 wt% than that for RBCs alone or RBC/A-300 at C A-300 = 0.01 wt.% because of structural changes in RBCs. Results of microscopic and XRD investigations and calculations using the TSDC-and NMR-cryoporometry suggest that the intracellular structures in RBCs (both organic and aqueous components) depend on nanosilica concentration in the suspension. [...]
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