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- Alkoxysilanes (1)
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Organisationseinheit der BAM
More and more sub-micro and nano-materials shall be "quickly", but accurately characterized with respect to their morphology, shape, size or size distribution, but also to the chemical composition as well by means of an SEM/EDX (Scanning Electron Microscopy / X-Ray Energy Dispersive Spectrometry) system. This undertaking is becoming successful indeed if the transmission mode at low voltages such as those at a SEM, i. e. mostly up to 30 kV, and EDX, respectively is employed. The transmission mode at conventional SEM can e "activated" firstly by re-defining the specimen to be analyzed and preparing it as a thin specimen, which is quasi-transparent to electrons and by finding a way of collecting only the transmitted electrons for analysis. The first issue can be easily realized by using the conventional TEM grids (and the respective sample preparation); the second one becomes feasible either (i) by placing a socalled STEM semiconductor detector directly under the thin specimen or (ii) by using a Special transmission set-up, which enables to the conventional Everhart-Thornley detector to collect only transmitted electrons by blocking the direct collection of secondary electrons and guiding only the transmitted electrons onto it.
The observation of morphological details down to the nanometer range of the outer surface of micro-, submicro- and nanoparticles in a high-resolution scanning electron microscope (SEM) was extended with in-depth observation by enabling the transmission mode in the SEM, i.e. TSEM. The micro- and nanocapsules characterized in this study were fabricated as depots for protective agents to be embedded in innovative self-healing coatings. By combining the two imaging modes (upper and in-depth observation) complementing each other a better characterisation by a more comprehensive interpretation of the 'consistency' of the challenging specimens, e.g. including details 'hidden' beyond the surface or the real specimen shape at all, has been attained. Furthermore, the preparation of the quasi electron transparent samples onto thin supporting foils enables also elemental imaging by energy dispersive X-ray spectroscopy (EDX) with high spatial resolution. Valuable information on the elemental distribution in individual micro-, submicro- and even nanocapsules completes the '3D' high resolution morphological characterization at the same multimodal SEM/TSEM/EDX system.
Selection and study of alkoxysilanes as loading in submicrocapsules for self-lubricating coatings
(2019)
The possibility and conditions for the formation of nano- or submicrocapsules loaded with hydrophobic active ingredients (alkoxysilanes) into the matrix of coatings with self-lubricating effect are considered. The optimal composition of the alkoxysilane submicrocapsules, and their physicochemical properties were determined. The longer the radical chain length is, the lower is the rate of hydrolysis, and, accordingly, the more stable is the formed emulsion. The methods of laser correlation spectroscopy in measuring the size and zeta potentials of the submicrocapsules with different loads of the active agent allowed to determine the optimal ratios of the active ingredients. The optimal concentration of the active agent is between 4 and 9%. Based on contact angle studies, octadecyltrimethoxysilane was selected as optimum compound. The introduction of 4 wt% of octadecyltrimethoxysilane reduces the friction coefficient of coatings by 20–30% under vibrating motion and by 15–20% under continuous motion. The data obtained can also be useful for the encapsulation of other hydrophobic active agents and for various other purposes, for example, for the introduction of biocidal agents.