Effect of Epoxy Oligomer on the Hierarchical Structure of Silica Nanoparticles Formed in a Polymer Matrix
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EFFECT OF EPOXY OLIGOMER ON THE HIERARCHICAL STRUCTURE OF SILICA NANOPARTICLES FORMED IN A POLYMER MATRIX S. V. Zhyltsova,1 N. G. Leonova,1 and E. A. Lysenkov 2
UDC 541.64:539.2
The structural features of epoxy-silica nanocomposites were studied using small-angle X-ray scattering and electron microscopy. It was shown that during the formation of sols of silica nanoparticles in the presence and absence of an epoxy oligomer in the system, their aggregation processes change significantly. Using fractal analysis, the type of fractal aggregates of each structural level is identified and their sizes are determined. It has been established that for systems formed in the presence of an epoxy oligomer, a predominantly two-level fractal organization is observed, at the first level of which mass-fractal aggregates with average sizes of 10-23 nm are formed, and at the second level, depending on the concentration of nanoparticles, they can form both mass and surface fractal aggregates with average sizes of 35-55 nm.
Key words: epoxy resin, tetraethoxysilane, sol-gel method, small-angle X-ray scattering, electron microscopy, fractal analysis, aggregates, nanocomposites.
Epoxy resin-based polymer nanocomposites are widely used in modern materials science: from multifunctional coatings to structural materials for marine and space industries [1, 2]. Such materials have improved thermophysical, mechanical, and antifriction properties when compared to the unfilled polymer [3, 4]. Size, content, and method of incorporation of particles into the polymer, synthesis conditions, as well as the interaction of particles with matrix play an important role in obtaining composites with adjustable functional characteristics. The sol-gel approach is one of the methods of obtaining epoxy nanomaterials with different structural organization of filler particles and, accordingly, different properties [5, 6]. It is based on the sequence of hydrolysis reactions of compounds containing alkoxide groups (in particular, silicon alkoxides), with the formation of hydroxyl-containing derivatives, and their subsequent condensation. Different factors affect the course of sol-gel synthesis, structure, and size of nanoparticles: solvent, temperature conditions, hydrolysis and condensation catalyst, pH, sequence of introduction of components, etc. [7-9]. The formation of sols of silica nanoparticles can occur both in the absence and in the presence of epoxy oligomer. The sol aging in the presence of an organic component slows down the processes of hydrolysis of alkoxysilane precursors and condensation of hydrolysis products [9], which enables one to obtain smaller particles. On the other hand, the course of secondary processes is possible in the formation of silica nanoparticles in the epoxy component medium, in particular, the ________ 1 Vasyl’ Stus Donetsk National University, Vinnytsia, Ukraine. E-mail: [email protected] 2 Petro Mohyla Black Sea National University, Mykolayiv, Ukraine ___________________________________________________________________
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