Controlled Silanization of Silica Nanoparticles to Stabilize Foams, Climbing Films, and Liquid Marbles

• Published in: Langmuir Vol. 27; no. 21; pp. 12869 - 12876
• Main Authors: Fletcher, Paul D. I, Holt, Ben L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.11.2011
• Subjects: Chemistry; Colloidal state and disperse state; Colloids: Surfactants and Self-Assembly, Dispersions, Emulsions, Foams; Emulsions. Microemulsions. Foams; Exact sciences and technology; General and physical chemistry; Physical and chemical studies. Granulometry. Electrokinetic phenomena; Solid-liquid interface; Surface physical chemistry; Water; Monolayer; Binary compound; Liquid particle; Film; Hydrophobization; Nanoparticle; Alcohol; Hydrophobicity; Silica; Synthesis; Energy; Alkanol; Structure; Uniformity; Methanol; Conductivity; Air; Contact angle; Dispersion; Liquid; Adsorption; Foam; Vapor phase; Reagents; Acid base titration; Silane; Room temperature
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la2028725

We describe a method for the synthesis of multigram amounts of silica nanoparticles which are controllably hydrophobized to different extents using a room temperature vapor phase silanization process. The extent of hydrophobization of the particles can be adjusted by changing the amount of dichlorodimethylsilane reagent used in the reaction. The method produces particles with good uniformity of surface coating; the silane coating varies from monolayer coverage at low extents of hydrophobization to approximately trilayer at high extents of hydrophobization. Acid–base titration using conductivity detection was used to characterize the extent of hydrophobization which is expressed as the percent of surface silanol groups remaining after silanization. Particles with %SiOH ranging from 100% (most hydrophilic) to 20% (most hydrophobic) were hand shaken with water/methanol mixtures and produced either a particle dispersion, foam, climbing films, or liquid marbles. The type of colloidal structure produced is discussed in terms of the liquid–air-particle contact angle and the energy of adsorption of the particles to the liquid–air surface.