Colloidal particles can spontaneously accumulate at the interface of two immiscible liquids and thereby stabilize disperse systems such as emulsions and foams [1]. Properly designed particles can adsorb irreversibly at the interface of an emulsion droplet, providing an unusually high stability of the system. In emulsion applications surface modified silica nanoparticles with controlled hydrophobicity and surface activity have great potential.
In this work, the properties of colloidal silica with hydrophobic and hydrophilic functionalizations are explored. The particles are evaluated and characterized to obtain knowledge of how they behave not only in dispersion systems, but also in terms of stability of the modification and steric stabilization effects. NMR diffusometry is used to evaluate the surface modification and is an essential tool for the characterization. The figure shows the diffusion profile of methyl polyethylene glycol silane (mPEG silane) grafted on silica particles with a specific surface area of 130m2/g. These particles are surface active and, at high enough coverage, sterically stabilized.
Figure 1: NMR diffusometry measurements (right) of silica particles grafted with mPEG silane (left). Before purification by ultrafiltration, 20% of the silanes (0.2µmol/m2) are attached to the particles, and after purification 85% of the silanes are attached to the particles. The steeper slope of the filtrated suspension is due to a more diluted sample with a lower viscosity.
Reference:
[1] Binks, B.P. and T.S. Horozov, eds.Colloidal Particles at Liquid Interfaces. 1 ed. 2006, CambridgeUniversity Press: New York.
sanna.bjorkegren@chalmers.se
