Abstract
Organosilicon layers chemically anchored on silica surfaces show high carbon content, good thermal and chemical stability and find numerous applications as fillers in polymer systems, thickeners in dispersing media, and as the stationary phases and carriers in chromatography. Methyl-terminated poly(dimethylsiloxanes) (PDMSs) are typically considered to be inert and not suitable for surface modification because of the absence of readily hydrolyzable groups. Therefore, in this paper, we report a new approach for surface modification of silica (SiO2) nanoparticles with poly(dimethylsiloxanes) with different lengths of polymer chains (PDMS-20, PDMS-50, PDMS-100) in the presence of diethyl carbonate (DEC) as initiator of siloxane bond splitting. Infrared spectroscopy (IR), elemental analysis (CHN), transmission electron microscopy (TEM), atomic force microscopy (AFM), rotational viscosity and contact angle of wetting were employed for the characterization of the raw fumed silica and modified silica nanoparticles. Elemental analysis data revealed that the carbon content in the grafted layer is higher than 8 wt % for all modified silicas, but it decreases significantly after sample treatment in polar media for silicas which were modified using neat PDMS. The IR spectroscopy data indicated full involvement of free silanol groups in the chemisorption process at a relatively low temperature (220 °C) for all resulting samples. The contact angle studies confirmed hydrophobic surface properties of the obtained materials. The rheology results illustrated that fumed silica modified with mixtures of PDMS-x/DEC exhibited thixotropic behavior in industrial oil (I-40A), and exhibited a fully reversible nanostructure and shorter structure recovery time than nanosilicas modified with neat PDMS. The obtained results from AFM and TEM analysis revealed that the modification of fumed silica with mixtures of PDMS-20/DEC allows obtaining narrow particle size distribution with uniform dispersity and an average particle size of 15–17 nm. The fumed silica nanoparticles chemically modified with mixtures of PDMS-x/DEC have potential applications such as nanofillers of various polymeric systems, thickeners in dispersing media, and additives in coatings.
Highlights
The hydrophobic nanodispersed silicas are widely used as thickeners in complex polar liquids based on epoxy, polyurethane, and vinylester resins
We can see that the carbon content is not practically changed after the treatment in organic solution for silicas modified with mixtures of PDMS-x/diethyl carbonate (DEC), which indicates that organosiloxanes are chemically bonded with the silica surface sites
The features of DEC chemisorption on a fumed silica surface were andwork, it wasthe found that the chemical interaction on of diethyl carbonate with sites the Inexamined, the present features of DEC
Summary
The hydrophobic nanodispersed silicas are widely used as thickeners in complex polar liquids based on epoxy, polyurethane, and vinylester resins. Partial depolymerization can be realized by different means: by thermal degradation (300–400 ◦ C) or by treatment with toxic agents such as alkalis, sulfuric acids, thionyl chloride, amines, and mixtures of alkali (NaOH, KOH) with alcohols (methanol, ethanol) [25,26,27,28,29,30] It should be noted, that the use of these catalysts is technologically complicated because of potential electrolyte presence in the obtained products, which are not desirable especially when using modified silicas as fillers in silicone cable rubbers and thickeners in insulating electrical greases
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