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    Changes of methylated silica surfaces on ageing

    Year: 2010

    Journal: Adsorbtion, Volume 16, Numbers 4-5, 271-277, 20111221

    Authors: Nora Schreithofer a, Janusz S. Laskowski b and Kari Heiskanen a

    Organizations: a Aalto University School of Science and Technology, Department of Materials Science and Engineering, Research Unit of Mechanical Process Technology and Recycling, P.O. Box 16200, 00076 Aalto, Finland, b University of British Columbia, N.B. Keevil Institute of Mining Engineering, Vancouver, BC, V6T 1Z4, Canada

    Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydrophobic be reacting with silane, change with time when the substrate is immersed in aqueous solution. Therefore the experimental conditions when such model systems are employed have to be carefully assessed.
    This paper summarizes the findings of the force measurement tests between air bubbles and silica particles hydrophobized with organosilanes such as trimethylchlorosilane and 1,1,1,3,3,3-hexamethyl-disilazane. The results showed that the attractive forces as well as the adhesion between the air bubbles and silica particles decrease with the time of aging in aqueous solution. The silica surfaces rendered hydrophobic with organosilanes become hydrophilic with time due to hydration. The hydrophobicity could be restored by heating the samples at 190 ○C.
    The atomic force microscopy imaging on silica plates revealed that in addition to hydration, decomposition of the organosilane layer also takes place.