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Adsorption Isotherm and Aggregate Properties of Fluorosurfactants on Alumina Measured by 19F NMR
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.ORCID iD: 0000-0002-0231-3970
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
2002 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 21, 8096-8101 p.Article in journal (Refereed) Published
Abstract [en]

The adsorption and self-assembly of ammonium perfluorooctanoate (APFO) at surfaces of porous alumina immersed in solution at pH similar to 4 have been studied using F-19 NMR. From the intensity of the APFO NMR signals, the amount of adsorbed surfactant, and thereby the adsorption isotherm, was determined. The adsorption isotherm indicates that APFO forms bilayers on alumina. This result is supported by finding the CF3 signal of adsorbed APFO shifted upfield compared to the signal in aqueous solution with an amount that corresponds to a change from aqueous to fluorocarbon environment. Additionally, faster transverse relaxation of the fluorine nuclei adjacent to the head group compared to that of the CF3 group adds a further argument for the formation of a bilayer. The exchange pattern of surfactants between the adsorbed layer and the aqueous bulk was studied through the CF3 group F-19 signals and their time-averaged behavior. Inside the pores of the alumina particles, the exchange time was found to be fast (much less than1 ms) between adsorbed and dissolved APFO. The presented NMR method to determine the adsorption isotherm could be a powerful new tool when studying systems of mixed surfactants, since the adsorbed amount of chemically different surfactants and their formation in aggregates would become separately quantifiable. The method is readily applicable to any NMR nuclei and thereby to many adsorption problems.

Place, publisher, year, edition, pages
2002. Vol. 18, no 21, 8096-8101 p.
Keyword [en]
Adsorption; Aggregates; Alumina; Ammonium compounds; Dissolution; Fluorocarbons; Isotherms; Nuclear magnetic resonance; pH effects; Porous materials; Self assembly; Solutions
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5686DOI: 10.1021/la026014vISI: 000178589700050OAI: oai:DiVA.org:kth-5686DiVA: diva2:10133
Note
QC 20100826Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2010-08-26Bibliographically approved
In thesis
1. Molecular Association Studied by NMR Spectroscopy
Open this publication in new window or tab >>Molecular Association Studied by NMR Spectroscopy
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This Thesis presents studies of molecular association in aqueous solution and at the liquid/solid interface. The investigated molecular systems range from self-aggregating surfactants to hydration water in contact with micelles or individual molecules. In most studies, combinations of various NMR methods were applied. These vary from simple chemical shift and intensity measurements to more elaborate self-diffusion and intermolecular cross-relaxation experiments.

Non-ideal mixed micelles of fluorinated and hydrogenated surfactants were studied by an experimental procedure that allows an analysis in terms of micellar structure, using a minimal number of initial assumptions. Quantitative conclusions about micro-phase separation within mixed micelles were obtained within the framework of the regular solution theory. Additionally, NMR was introduced and developed as a powerful method for studying adsorption of surfactants at solid interfaces. Adsorption isotherms for pure and mixed surfactant systems and non-ideal mixing behavior of fluorinated and hydrogenated surfactants at solid surfaces were quantified. Fluorosurfactant-protein association was investigated using the methods described.

Intermolecular cross-relaxation rates between solute and solvent molecules were recorded at several different magnetic fields. The results reveal strong frequency dependence for both small molecules and micelles. This finding demonstrates that intermolecular cross-relaxation is not solely controlled by fast local motions, but also by long-range translational dynamics. Data analysis in terms of recently developed relaxation models provides information about the hydrophobic hydration and micellar structure.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 52 p.
Series
Trita-FYK, 0602
Keyword
NMR, spin relaxation, self-diffusion, intermolecular cross-relaxation, chemical shift, fluorinated surfactants, hydrogenated surfactant, micelle, non-ideal mixing, adsorption, hydration, surfactant-protein association
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-3947 (URN)91-7178-345 8 (ISBN)
Public defence
2006-05-19, F3, Lindstedtsv. 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100914Available from: 2006-05-10 Created: 2006-05-10 Last updated: 2010-09-14Bibliographically approved

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