Impact of sol mixture composition on organosilica coatings formation on glass substrates

In this study, hybrid organosilica coatings on glass substrates were synthesized using mixtures of the active polymer OH-terminated PDMS and one or more precursors, namely methyltrimethoxysilane bis(3-trimethoxysilylpropyl) amine, phenyltrimethoxysilane, cyanopropyltrimethoxysilane, aminopropyltriethoxysilane in the presence of modifiers (polyethylene glycol, organic solvents) and trifluoroacetic acid catalyst. The aim of this work was to obtain new sorption materials for the extraction of nonpolar and semi-polar analytes, for example, carbonyl compounds in the form of PFBHA derivatives, azo dyes, phthalates, and others, and to purify samples with a complex matrix for further gas chromatographic analysis. The advantages of the obtained sorption coatings are the effective separation of micro quantities of target compounds of nonpolar and semi-polar nature from polar compounds present in aqueous samples in rather high concentrations. The paper describes the synthesis of organosilica coatings of various compositions, the volume ratio of the active polymer, precursors, deactivating agent, catalyst, and modifiers. The coatings were applied to glass substrates using two methods: spin-coating and dip-coating. Sometimes the application was complicated due to uneven distribution of the sol when the solution mixture was too viscous or required a long drying time. Bis(3-trimethoxysilylpropyl) amine and N-(2-aminoethyl)-3-aminopropyltriethoxysilane proved to be effective crosslinking agents with similar properties of the obtained coatings; the addition of these precursors significantly improved the characteristics of the obtained coatings. It has been shown that mixtures containing OH-terminated PDMS form thick coatings (up to 325 μm) without cracks in the presence of most of the studied precursors, and the addition of titanium isopropoxide improves the thermal stability and leads to the formation of a more uniform coating in the case of substrates of complex shape (stir bars). The IR spectra of the studied coatings were obtained, most of the spectral bands are typical of the PDMS polymer, and the presence of covalently bound titanium in the coatings is confirmed by a peak at 924 cm–1. All the coatings were hydrophobic, and the contact angles with water were measured, which ranged from 99.7 to 105.6. Thermogravimetric analysis (TG and DTA) was performed to verify the thermal stability of the coatings for further use in solid-phase microextraction with gas chromatography, and it was shown that the coatings could withstand heating up to 350–425 ℃. For sorption in analytical quantitative methods, it is necessary to use coatings that are homogeneous, uniform, durable, less prone to swelling, and reproducible in synthesis and during sorption. The synthesized coatings are effective for further use in chemical analysis to purify samples from interfering components or for preconcentration of analytes. The coatings have sufficient stability to be used in the hybrid methods of analysis.