Abstract
Adsorption of a short-chain nonionic amphiphile (C6E3) at the surface of mesoporous silica
glass (CPG-10) was studied by a combination of adsorption measurements and mesoscale
simulations. Adsorption measurements covering a wide composition range of the C6E3 + water
system show that no adsorption occurs up to the critical micelle concentration (cmc), at which
a sharp increase of adsorption is observed that is attributed to ad-micelle formation at the
pore walls. Intriguingly, as the concentration is increased further, the surface excess of the
amphiphile begins to decrease and eventually becomes negative, which corresponds to
preferential adsorption of water rather than amphiphile at high amphiphile concentrations.
The existence of such a surface-azeotropic point has not previously been reported in the
surfactant adsorption field. Dissipative particle dynamics (DPD) simulations were performed to
reveal the structural origin of this transition from aggregative adsorption to surface depletion.
The simulations indicate that this transition can be attributed to the repulsive interaction
between head groups, causing amphiphilic depletion in the region around the corona of the
surface micelles.
