Chemistry, Physics and Technology of Surface

ISSN 2518-1238 (Online), ISSN 2079-1704 (Print)

The aim of this work was to search the colloidal systems characterized by maximal effects of water interaction with a solid surface and micro-coagulation, as well development of control methods of thixotropic properties, by addition of solid and liquid hydrophobic compounds into the colloidal systems. Water state and its thermodynamic characteristics, namely the values of free interfacial energy for concentrated colloidal systems based on hydrated blends of hydrophobic compounds (polymethylsiloxane, PMS and methylated nanosilica AM1) and hydrophilic nanosilica A-300, were studied using low-temperature ¹H NMR spectroscopy and electron microscopy. It was established that the free interfacial energy of water, determining the thixotropic properties of the concentrated suspensions under condition of great hydration, is firstly affected by the structure of inter-particulate space, especially by the nanocoagulation effects and influence of a surface on the formation of the hydrogen bonds network in the adsorption layer. For the blend with A-300 and AM1 (1:1 w/w), the free surface energy of interaction with water is nearly ten times greater than that for the initial silicas alone. However, the micro-coagulation effects are poorly visible in microscopic images because these oxides are composed of similar nanoparticles. Similar effects of enhancement of the free surface energy are observed for a blend with A-300 and PMS. For this blend, the micro-coagulation effect is observed in microscopic images. It is maximal for the blend prepared without strong mechanical loading. PMS has a twice greater surface area than that of A-300. Therefore, water filling voids in PMS aggregates forms clusters of smaller sizes than that bound in A-300. However, hydrophilicity or hydrophobicity is not a predominant factor determining the free surface energy of bound water. If strongly hydrated treated powders of PMS (or AM1) and A-300 are placed into a hydrophobic medium with weakly polar CDCl₃ that this solvent could diffuse into hydrophobic component and displace water from narrow interparticle voids toward larger ones. However, this effect is much weaker for a hydrophilic component with A-300. These effects appear in a strong dependence of the γ_S value on the type of the dispersion medium for PMS and a weak dependence for A-300. The stronger the decreasing effects of a hydrophobic liquid onto the γ_S value, the stronger is diminution of the thixotropic properties on the composites. The blends of hydrophobic and hydrophilic powders with the bulk density < 0.2 g/cm³ are most perspective thixotropic compositions since they demonstrate the maximal values of γ_S and a strong microcoagulation effect.

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