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Adsorption of Alkyl Polyglucosides on the Solid/Water Interface: Equilibrium Effects of Alkyl Chain Length and Head Group Polymerization
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
2004 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, no 10, 4051-4058 p.Article in journal (Refereed) Published
Abstract [en]

The equilibrium adsorption behavior of two n-alkyl-beta-D-glucosides (octyl (C(8)G(1)) and decyl (C(10)G(1))) and four n-alkyl-beta-D-maltosides (octyl(C(8)G(2)), decyl (C,(10)G(2)), dodecyl(C(12)G(2)) and tetradecyl (C(14)G(2))) 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 headgroup polymerization, but a comparison with their adsorption on the silica/water and air/water interfaces 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 the critical micelle concentration (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. Headgroup 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 the cmc. When compared with the ethylene oxide (EO) 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.

Place, publisher, year, edition, pages
2004. Vol. 20, no 10, 4051-4058 p.
Keyword [en]
Adsorption; Ellipsometry; Free energy; Polymerization; Quartz; Refractive index; Surface properties; Titanium; Wetting
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-6507DOI: 10.1021/la035959pISI: 000221319400036Scopus ID: 2-s2.0-2542560417OAI: oai:DiVA.org:kth-6507DiVA: diva2:11240
Note
QC 20100826Available from: 2005-09-19 Created: 2005-09-19 Last updated: 2011-10-25Bibliographically 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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