Colloidal Gels Of Fumed Silica Microstructure Surface Interactions And Temperature Effects

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Download or read book Colloidal Gels of Fumed Silica: Microstructure, Surface Interactions and Temperature Effects written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The interactions of fumed oxides with organic solvents, polymers and biological systems are of great interest as they can be utilized as viscosity modifiers, fillers or adsorbents when mixed in or in contact with such materials. Fumed silica is of particular interest due to the large surface area that its branched structure provides for establishing interactions with specific matrices or chemical reactive groups. If these small particles are dispersed in an adequate medium, they can form suspensions, flocculated systems or three-dimensional networks; thus an understanding of how to control this microstructure is of paramount importance. Extensive research involving fumed silica dispersions has been conducted in areas such as inks, cosmetics, and paints. More recently, alternative novel applications such as fiber optic cables and composite polymer electrolytes, our major research effort in the past years, have gained especial importance. In this work, various types of fumed silica particles have been dispersed in different oligoethers and poly(ethylene oxide) PEO and their properties evaluated with the aim to finely tune them for improved performance during end use. Rheology, a reliable, easy, and readily available technique has been employed not only to characterize the systems, but also to study their microstructure and establish correlations that can be subsequently employed to tailor the material for the particular application. In particular, we examined dispersions of hydrophobic and hydrophilic fumed silica in oligoethers of different molecular weights and end group composition at different temperatures by using dynamic rheology. We observed that hydrophilic fumed silica particles form gels in the less polar oligoethers, whereas the hydrophobic ones form a network in all the oligoethers employed. Increasing the temperature increases irreversibly the gel modulus of the system containing hydrophilic fumed silica and the oligoether with the largest end group conte.