Enhanced adsorption of alkyl glucosides on the silica/water interface by addition of amine oxides

• The effect of adding a small amount of dodecyl dimethyl amine oxide (DDAO) on adsorption on silica from an aqueous solution of dodecyl maltoside (C12G2) has been investigated. The C12G2 itself does not adsorb significantly on silica at any concentration. DDAO on the other hand readily adsorbs in a bilayer-like structure at concentrations approaching cmc, but the adsorbed amount at the concentrations it has been applied in these mixtures is small. In contrast, by combining the two surfactants significant adsorption is observed at concentrations where the adsorption of the pure DDAO, as well as pure C12G2, is very low. We thus see a strong enhancement of the adsorption from the mixed system. The adsorption is suggested to be a two-step process, where individual DDAO molecules first adsorb to the silica surface through electrostatic interactions, and then C12G2 adsorbs at the hydrophobic sites the DDAO tails constitute through hydrophobic bonding. A minimum concentration of DDAO is required to induce adsorption from a solution with constant C12G2 concentration. This concentration is lower for C12G2 solutions below and equal to cmc than above cmc. In addition, the total adsorbed amount shows a maximum around cmc of the mixture for a solution with low DDAO contents. Both these effects are explained by incorporation of DDAO in the C12G2 micelles above cmc, which leads to a desorption of DDAO from the surface.

Nyckelord

Adsorption

alkyl polyglucoside

oxide

titania

silica

non-ionic surfactant

ellipsometry

sugar based surfactant

co-adsorption

amine oxide

DDAO

APG

LDAO

synergism

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