Füllstoff-Elastomer-Wechselwirkungen: Oberflächenenergie von silan-modifizierten Kieselsäuren
von M.-J. Wang u. S. Wolff
As shown in previous papers of this series, the main feature of silica with regard to surface energy, which distinguishes them from carbon-blacks, is a low dispersive compound, ysd and a high specific component, yssp, of surface energy. The low ysd would result in a lack of interaction between filler and hydrocarbon rubbers, while the high yssp would suggest a high degree of agglomeration of the filler particles in the polymer matrix. In this study, the surface free energies and the energy distribution on the surfaces of preciptated silicas which had been modified with octadecyltrimethoxy silane, 3-thiocyanatopropyltriethoxy silane and bis (3-trimethoxysilypropyl) - tetrasulfane respectively, were investigated by chromatography at infinite dilution and at finite concentration. A comparison with the initial silica suggests a drastic decrease in surface energy, especially of the specific component, as a result of the modification and a strong dependence of surface energy on the chemical nature of the grafts and the ratio of these grafts. The energy distribution function shows that, while the surface of the ungrafted silica is heterogeneous, the heterogeneity of the fully modified surface is drastically reduced, particulary when the product was modified with octadecyltrimethoxy silane.