Andrzej Krysztafkiewicz

Influence of silane coupling agents on surface properties of precipitated silicas

Silicas of highly dispersion degree were obtained. This process includes formation of silica particles and their aggregation. The ethylene glycol solution was used in precipitation process, resulting in a partial blocking of the silica surface hydroxyl groups (silanol groups) and, thus, in a decreased hydrophilicity of silica. Studies on the surface modification of silicas using silane coupling agents are described. The best modifiers were selected, which inducted a change of the silica surface from hydrophilic to hydrophobic. Basic physicochemical analyses of the obtained silicas were performed. The methods of evaluating the degree of surface modification of the silica were presented. Near infrared spectroscopy (NIR) was used to determine the degree of condensation of the silica surface silanol groups. The degree of hydrophobization of silica surface was determined by a calorimetric method. Moreover, studies on morphology and microstructure using transmission electron microscopy (TEM) were performed. Size distribution of primary particles and aggregates and agglomerates structures were determined by ZetaPlus instrument using dynamic light scattering (DLS) method.

Preparation of the hydrophilic/hydrophobic silica particles

Abstract Silicas of high dispersion degree were obtained. The process included formation of silica particles and their aggregation. Glycerin solution was used in precipitation process, resulting in a partial blocking of the silica surface hydroxyl groups (silanol groups) and, thus, in a decreased hydrophilicity of silica. Studies on the surface modification of silicas using silane coupling agents are described. The best modifiers were selected, which induced a change of the silica surface from the hydrophilic to the hydrophobic one. Basic physicochemical analyses of the obtained silicas were performed. Near infrared spectroscopy (NIR) was used to determine the degree of condensation of silica surface silanol groups. The degree of hydrophobization of silica surface was determined by a calorimetric method. Moreover, zeta potential, size distribution of primary particles, aggregates and agglomerates structures were determined by ZetaPlus instrument using electrophorectic (ELS) and dynamic (DLS) light scattering techniques.

Adsorption of dyes on a silica surface

Abstract Adsorption of several organic dyes was examined on a modified silica surface. For this purpose, EG-Silica was applied, precipitated from sodium metasilicate solution using carbon dioxide in presence of ethylene glycol. In order to promote their interaction with dyes, the silica surface was modified using silane coupling agents with the amino functional group. Technique of conducting the adsorption process was discussed. Studies on morphology and microstructure were performed employing scanning electron microscopy (SEM). Particle size distribution was also examined using the technique of dynamic light scattering. The SEM micrographs and particle size distributions showed that highly uniform pigments can be obtained employing EG-Silica as a core. Studies on elution of dyes from the silica surface demonstrated that, in general, stable pigments were obtained.

Physicochemical and morphological properties of hydrated silicas precipitated following alkoxysilane surface modification

Abstract Modified silicas were obtained by precipitation from aqueous solutions of sodium metasilicate and sulphuric acid. For the modification, silane coupling agents with various functional groups were applied, including aminosilane (AEAPTS), glycidoxysilane (GPTS), mercaptosilane (McPTS), and vinylsilane (VTMES). Extensive physicochemical evaluation of the obtained modified silicas was conducted, using FTIR, 29 Si CP MAS NMR and XPS techniques. The silica surface modification was proven to depend upon chemical reactions and to show intensity increasing with a rising concentration of a given modifier. A surface charge of the formed silica dispersions was also examined, by determining their zeta potential. Moreover, surface morphology, dispersion and particle size of the obtained silicas were evaluated, employing TEM electron microscopy and the technique of a dynamic light scattering (DLS). The studies demonstrated that application of hydrophobic type silanes for surface modification of the hydrated silicas restricted the intense tendency for agglomeration in the formed precipitated silicas.

Preparation of pigments on modified precipitated silicas

Pigments were obtained by attaching C.I. Direct Red 81 dye to a modified silica surface. Two types of precipitated silicas were applied, namely the commercial Syloid 244 and the precipitated EG-SILICA which was prepared according to a novel procedure. The silica surface was modified with silane coupling agents, such as 3-aminopropyltriethoxysilane and N-2-(aminoethyl)-3-aminopropyltrimethoxysilane. The staining process was conducted in an aqueous suspension of silica in the presence of the dye. Various amounts of modifiers were applied in order to determine their effect on the dye adsorption process. The physicochemical, structural and microscopic properties of the modified silicas and of the obtained pigments were examined.

The effect of surface modification on physicochemical properties of precipitated silica

The main goal of this study was to obtain hydrophobic silica whose properties would allow their application as plasto- and elastomer fillers. Thus, hydrated silica was modified by silane and titanate coupling agents. The modification procedure and appropriate modification apparatus were developed. The degree of silica surface modification was evaluated by different methods. As grounds for this evaluation, changes in the physicochemical properties, brought about by the condensation reaction of surface silanol groups with alkoxyl or hydroxyl groups of the molecules of coupling agents, were used. The degree of hydrophobicity of the silica surface was determined on the basis of the heat of immersion of this surface, and silanol groups were identified by the infrared spectroscopy. Moreover, changes in the tendency to form agglomerates and aggregates of molecules were studied by microscopy. It was found that modification with silane and titanate coupling agents leads to an increase in silica activity. Application of these agents results in the change of the hydrophilic character to the hydrophobic one.

Precipitated silicas modified with 3-aminopropyltriethoxysilane

Abstract A comparison was made of the methods used to modify the surface of hydrated silicas employing aminosilane coupling agent. The so-called dry technique of modification and the newly elaborated technique of modification in the course of precipitation were applied. The extent of modification of precipitated silicas was determined on the basis of heats of immersion of silica surface and of spectrophotometric analysis. Morphology of silica particle surface and size distribution of silica particles were determined by transmission electron microscopy (TEM) and by ZetaPlus instrument using dynamic light scattering.

Modified calcium silicates as active rubber fillers

The physicochemical characteristics of calcium silicates obtained from the reaction of sodium metasilicate solution with calcium nitrate are given. Further, studies of the modification of the silicate surface with silane and titanate coupling agents are presented. By wettability measurements and an analysis of the chemically adsorbed carbon arising from the coupling agents, the degree of modification of these surfaces was estimated. The modification of the surface of the silicates with the same agents, but in the presence of acid protons, was also performed with a positive effect. The usefulness of modifications is justified by the results of strength studies of vulcanizates filled with the modified silicates.

Effect of N-2-(aminoethyl)-3-aminopropyltrimethoxysilane surface modification and C.I. Acid Red 18 dye adsorption on the physicochemical properties of silica precipitated in an emulsion route, used as a pigment and a filler in acrylic paints

Abstract Studies were performed on the synthesis of spherical silica particles in an emulsion route, and its surface modification using N -2-(aminoethyl)-3-aminopopyltrimethoxysilane. Onto the aminosilane-treated silica surface, C.I. Acid Red 18 dye was adsorbed. The ensuing silica and its derivatives were subjected to comprehensive physicochemical and dispersion analysis. Both the size and shape of the particles were estimated and the surface specific area (BET) and porosity were characterised using adsorption/desorption curves. Moreover, chemical and surface compositions were determined using elemental analysis and XPS. A mechanism was suggested for the interaction betweeen the aminosilane-modified silica and an organic dye. The obtained pigment was tested in an acrylic paint system; the precipitated monodisperse silica was found to exhibit optimum properties as a carrier of organic dye, particularly after modification of the former with aminosilane, thus acting as a valuable filler and pigment in modern paint systems.

Effect of silane coupling agents on properties of precipitated sodium–aluminium silicates

Abstract Sodium–aluminium silicates of highly dispersion degree were obtained. Studies on the surface modification of sodium–aluminium silicates using silane coupling agents are described. The best modifiers were selected, which induced a change of the silicate surface from a hydrophilic to a hydrophobic one. Physicochemical analyses of the obtained silicates were performed. The methods of evaluating the degree of surface modification of the silicate were presented. Near infrared spectroscopy was used to determine the degree of condensation of the silicate surface silanol groups. The degree of hydrophobization of silicate surface was determined by a calorimetric method. Studies on morphology and microstructure using transmission electron microscopy were performed. Moreover, particle size and tendency to form primary and secondary agglomerate structures were determined.