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Mesoporous Silica Colloids: Wetting, Surface Diffusion, and Cationic Surfactant Adsorption
journal contribution
posted on 2019-10-18, 18:43 authored by Elise Azar, Christophe Blanc, Ahmad Mehdi, Maurizio Nobili, Antonio StoccoWe
have investigated the wetting and surface diffusion of mesoporous
colloidal silica particles at the water surface and the adsorption
of cationic cetyltrimethylammonium (CTA+) surfactant on
these particles. Porous silica colloids diffuse at the surface of
water and in the volume, interacting with cationic surfactants that
can adsorb inside the pores of the particles. We observed that surfactant
adsorption on mesoporous silica depends dramatically not only on the
particle pore size but also on specific counterion effects. We measured
striking differences both on a macroscopic property of the interface,
i.e., surface tension, and also at a single particle level by evaluating
the translational diffusion of partially wetted particles at the fluid
interface. We varied the pore size from 2 to 7 nm and explored the
effects of ions possessing different hydration number and kosmotropic/chaotropic
character. At concentrations lower than the critical micellar concentration,
we evidence that cationic surfactants adsorb on silica as surface
micelles and surfactant adsorption inside the pores occurs only if
the pore diameter is larger than the size of surface micelles. With
a view to understand the surprising different adsorption behavior
of CTA+OH– and CTA+Br– on porous silica particles, we investigated the effect
of counterions on the surfactant adsorption on porous silica colloids
by tuning the pH and the counterion properties.