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Enhanced Adsorption of Alkyl Glucosides on the Silica/Water Interface by Addition of Amine Oxides
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
2005 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, no 7, 2766-2772 p.Article in journal (Refereed) Published
Abstract [en]

The effect of adding a small amount of dodecyl dimethylamine oxide (DDAO) on adsorption on silica from an aqueous solution of dodecyl maltoside (C(12)G(2)) has been investigated. The C(12)G(2) 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 the critical micelle concentration (cmc), but the adsorbed amount at the concentrations it has been applied in these mixtures is small. In contrast, by combination of the two surfactants, significant adsorption is observed at concentrations where the adsorption of the pure DDAO, as well as pure C(12)G(2), 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 C(12)G(2) 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 C(12)G(2) concentration. This concentration is lower for C(12)G(2) solutions below and equal to cmcC(12)G(2) than above cmc(C12)G(2). In addition, the total adsorbed amount shows a maximum around cmcC(12)G(2) of the mixture for a solution with low DDAO contents. Both these effects are explained by incorporation of DDAO in the mixed micelles above cmc(mix)., which leads to a desorption of DDAO from the surface.

Place, publisher, year, edition, pages
2005. Vol. 21, no 7, 2766-2772 p.
Keyword [en]
Adsorption, Amines, Chemical bonds, Desorption, Hydrophobicity, Interfaces (materials), Micelles, Oxides, Refractive index, Silica, Water
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-6509DOI: 10.1021/la049173iISI: 000228042400025Scopus ID: 2-s2.0-16244401985OAI: oai:DiVA.org:kth-6509DiVA: diva2:11242
Note

QC 20100913

Available from: 2005-09-19 Created: 2005-09-19 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Adsorption of polyhydroxyl based surfactants
Open this publication in new window or tab >>Adsorption of polyhydroxyl based surfactants
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Adsorption on solid surfaces from solution is a fundamental property of a surfactant. It might even be the most important aspect of surfactant behavior, since it influences many applications, such as cleaning, detergency, dispersion, separation, flotation, and lubrication. Consequently, fundamental investigations of surfactant adsorption are relevant to many areas.

The main aim of this thesis has been to elucidate the adsorption properties, primarily on the solid/water interface, of a particular class of polyhydroxyl based surfactants: the alkyl glucosides. By the use of ellipsometry, the equilibrium and kinetic aspects of adsorption on titanium dioxide with respect to structural effects has been studied. Furthermore, the effects of small amounts of cationic surfactant additives on the adsorption on silica have been investigated. The results have been compared with similar studies for other nonionic surfactants.

We have found that the surfactant structure has a strong effect on the adsorption properties. An increase in the surfactant chain length increases the cooperativity of the system. An increase in the head group polymerization decreases the cooperativity and the plateau adsorbed amount at equilibrium. The effect of surfactant structure on the adsorption kinetics depends on the concentration relative to the cmc, while the there is a decrease in the rate of desorption with increasing hydrophobic chain length independent of the concentration. The adsorption/desorption process is concluded to be diffusion driven, as suggested by the model used. When comparing these results with studies on ethylene oxide based surfactants, we conclude that the two types of surfactants exhibit similar trends on surfaces onto which they adsorb.

Adsorption from binary surfactant solutions is even more interesting than adsorption from single surfactant solutions, since it brings us one step closer to the systems used in applications. In addition, adsorption from a mixture can be very different from adsorption from any of the single surfactants in the mixture. Alkyl glucosides alone do not adsorb on silica, but addition of small amounts of a cationic surfactant to the alkyl glucoside solution allows for adsorption on silica. A comparison between the adsorption and bulk properties has shown that mixed micellization explains most, but not all, effects of the coadsorption properties. Changing the pH in the mixed systems reveals that a surfactant with a pH-dependent charge and the ability to adapt its charge to the environment, e.g. a surface, enhances the adsorbed amount over a wider range of pH values than a purely cationic surfactant.

It is well known that alkyl glucosides and ethylene oxides adsorb differently on different types of hydrophilic surfaces. As a consequence, replacing ethylene oxides with alkyl glucosides might not be all straight-forward; however, we have shown that the effect of the surface can be eliminated by the use of a cosurfactant.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. x, 50 p.
Series
Trita-YTK, ISSN 1650-0490 ; 0503
Keyword
Physical chemistry, surface chemistry, adsorption, surfactant, nonionic, alkyl glucoside (APG), ellipsometry, kinetics, alkyl amine oxide (DDAO), alkyl ammonium bromide (DTAB), solid/liquid interface, synergism, coadsorption.
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-421 (URN)91-7178-146-3 (ISBN)
Public defence
2005-09-29, Q2, Osquldas väg 53, Stockholm, 14:00
Opponent
Supervisors
Note

QC 20101018

Available from: 2005-09-19 Created: 2005-09-19 Last updated: 2012-09-24Bibliographically approved

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