Some peculiarities of the surface chemical modification of the high‐dispersed silica fillers

Abstract

Advantageous routes of preparation of dense hydrophobic coverings on the silica surface are discussed. An analysis of the experimental data allows to realize the optimum choice of modifying reagents and catalysts for the surface reactions. Possibilities of the use of solid-phase hydrosilylation reactions for this purpose are examined. INTRODUCTJONChemical modification of silica fillers surface allows to improve a particle distribution in the polymeric medium. In favourable cases the physico-mechanical properties of the Wed system may be essentially changed as a result of interaction between the lhctional groups of the filler surface and polymeric macromolecules. The chemical reactions of organic and organosilicon compounds with silanol groups of the silica surface resulted in both the preparation of the fillers with different ratios of the hydrophobic or hydrophilic sites and the synthesis of the fillers with chemically active groups in the grafted surface layer. Many factors have influence on the proceeding chemical reactions involving silica surface, namely, nature and reactivity of the surface sites, electronic and geometrical structure of the modifying reagent, conditions of realization of the chemisorption process, the state of hydrate covering of the silica surface, presence of electron-and proton-donating molecules in the reaction volume. Neglect of these factors may be responsible for the fact that when treating the silicas with the specified geometry with the same reagent one may obtain the modified fillers with non-reproducible surface properties. The accumulated experience allows to pick out some advanced routes for the creation of different dense modifylng layers on the silica surface. RESULTS AND DISCUSSIONI . The optimum choice of modifylng reagent with the high reactivity toward the surface sites. Analysing the reactivity of trimethylsilylating reagents of the common formula (CH3)SiX, where X is halogen, alkoxy-or other group reactive with respect to silanol groups of the silica surface, it was established (Ref 1) that the most dense modifylng coverings were obtained by using organosilicon compounds with bond Si-N(H.R). in particular hexamethyldisilazane or trimethyl(dimethylamino)silane. The observed sequence of activities: organosilazanes > otganoalkoxysilanes > organochlorosilanes may be considered as an adequate argument in

The Effect of Surface Modification of Silica Microfillers in an Epoxy Matrix on the Thermo-mechanical Properties

“…In these cases very high fracture toughness can be reached when the fracture mechanism entails crack propagation around the edge of the parti-cle. Furthermore, it is well known that the reinforcing potential of a filler is greatly dependent on the quality of its dispersion in the matrix [9,10], and the particle size and agglomeration distribution affect the rheological properties of the polymer composite system [11]. Thus, it is crucial to characterize the extent of dispersion.…”