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- Matsson, MK, et al.
(författare)
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Adsorption of alkyl polyglucosides on the solid/water interface: Equilibrium effects of alkyl chain length and head group polymerization
- 2004
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 20, s. 4051-4058
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium adsorption behavior of two n-alkyl-b-D-glucosides (octyl, C8G1 and decyl, C10G1) and four n-alkyl-β-D-maltosides (octyl, C8G2, decyl, C10G2, dodecyl, C12G2 and tetradecyl, C14G2) from aqueous solution on a titania surface, as measured by ellipsometry, has been investigated. The main focus has been on the effect of changes in the alkyl chain length and head group polymerization, but a comparison with their adsorption on the silica/water and air/water interface is also presented. Some comparison with the corresponding adsorption of ethylene oxide surfactants, in particular C10E6 and C12E6 is given as well. For all alkyl polyglucosides, the maximum adsorbed amount on titania is reached slightly below cmc where it levels off to a plateau and the amount adsorbed corresponds roughly to a bilayer. However, there is no evidence that this is the actual conformation of the surfactant assemblies on the surface, but the surfactants could also be arranged in a micellar network. On hydrophilic silica, the adsorbed amount is a magnitude lower than on titania, corresponding roughly to a layer of surfactants lying flat on the surface. A change in the alkyl chain length does not result in any change in the plateau molar adsorbed amount at equilibrium, however the isotherm slope for the alkyl maltosides increases with increasing chain length. Head group polymerization on the other hand affects the adsorbed amount. The alkyl glucosides start adsorbing at lower bulk concentrations than the maltosides and equilibrate at higher adsorbed amounts above cmc. When compared with the ethylene oxide surfactants, it is confirmed that the EO-surfactants hardly adsorb on titania, since the measured changes in the ellipsometric angles are within the noise level. They do, however, adsorb strongly on silica
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| 2. |
- Matsson, MK, et al.
(författare)
-
Enhanced adsorption of alkyl glucosides on the silica/water interface by addition of amine oxides
- 2005
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 21, s. 2766-2772
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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