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The effect of adsorbed layer surface roughness on the QCM-D response: focus on trapped water
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).ORCID iD: 0000-0001-7496-1101
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 24, 12436-12444 p.Article in journal (Refereed) Published
Abstract [en]

The effect of surface roughness on the quartz crystal microbalance with dissipation monitoring (QCM-D) response was investigated with emphasis on determining the amount of trapped water. Surfaces with different nanoroughnesses Were prepared on silica by self-assembly of cationic surfactants with different packing parameters. We used surfactants with quaternary ammonium bromide headgroups: the double-chained didodecyltrimethylammonium bromide (C-12)(2)-DAB (DDAB), the single-chained hexadecyltrimethylammonium bromide C(16)TAB (CTAB), and dodecyltrimethylammonium bromide C(12)TAB (DTAB). The amount of trapped water was obtained from the difference between the mass sensed by QCM-D and the adsorbed amount detected by optical reflectometry. The amount of water, which is sensed by QCM-D, was found to increase with the nanoroughness of the adsorbed layer. The water sensed by QCM-D cannot be assigned primarily to hydration water, because it differs substantially for adsorbed surfactant layers with similar headgroups but with different nanoscale topographies

Place, publisher, year, edition, pages
2007. Vol. 23, no 24, 12436-12444 p.
Keyword [en]
Adsorption; Cationic surfactants; Energy dissipation; Quartz crystal microbalances; Reflectometers; Surface roughness; Dissipation monitoring; Optical reflectometry; Trapped water; Polymer films
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-7417DOI: 10.1021/la7014308ISI: 000250976700077Scopus ID: 2-s2.0-36649000928OAI: oai:DiVA.org:kth-7417DiVA: diva2:12438
Note

QC 20100809

Available from: 2009-08-30 Created: 2009-08-30 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Interactions Between Biopolymers and Surfactants with Focus on Fluorosurfactants and Proteins
Open this publication in new window or tab >>Interactions Between Biopolymers and Surfactants with Focus on Fluorosurfactants and Proteins
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The aim of this thesis was to obtain a better understanding of the association between surfactants and biopolymers in bulk solutions and at solid/aqueous liquid interface. In order to do this, the interactions between surfactants and biopolymers were investigated with a variety of experimental techniques.

The main focus has been on the interactions between fluorosurfactants and proteins, which are important during electrophoresis of proteins in silica capillaries. Electrophoretic separation of positively charged proteins is often complicated by non-specific adsorption of protein onto capillary wall, while it was found to improve when cationic fluorosurfactants were added into the background buffer. We investigated the interactions between a cationic fluorosurfactant, FC134, and a positively charged protein, lysozyme. By employing Nuclear Magnetic Resonance (NMR) and tensiometry we could conclude that the cationic fluorosurfactant did not associate with positively charged lysozyme in bulk solutions. At the solid/aqueous liquid interface, the adsorption of fluorosurfactants and lysozyme onto silica was studied by the surface force technique (MASIF), ellipsometry, reflectrometry, Quartz Crystal Microbalance (QCM-D) and Atomic Force Microscopy (AFM). Cationic fluorosurfactant FC134 was found to adsorb onto the silica surface in a form of bilayer aggregates, which led to a charge reversal of the originally negatively charged substrate. The adsorption of lysozyme onto silica was also extensive and it corresponded to the more than monolayer coverage. When adsorbing from mixed solutions, the presence of the cationic fluorosurfactant in the solution led to an elimination of the lysozyme in the resulting adsorbed layer. For the lysozyme concentration of 0.2 mg/ml, which is typical for the electrophoretic separation, it was found that adsorption of protein was suppressed by more than 90% when only 30 μM of FC134 was added into the buffer. The presence of the low amounts of residual proteins in the adsorbed layers caused an enhancement of the adsorption of fluorosurfactants, which was attributed to adsorption of the fluorosurfactants between proteins in a form of large vesicles.

The interactions between a positively charged biopolymer chitosan and an anionic surfactant sodium dodecylsulfate (SDS) were studied with respect to the effect of the ionic strength of the background electrolyte, both in the bulk solution and at the silica/liquid interface. It was shown that SDS and chitosan form complexes in the bulk solution, which reverse their charge at higher SDS concentrations. At SDS concentrations above the critical micellar concentration, large aggregates were formed, which were trapped in long-lived nonequilibrium states at both high and low ionic strengths. SDS did not adsorb at the silica/liquid interface by itself. However, by employing QCM-D and ellipsometry we detected an extensive adsorption of SDS on the silica substrate, which has been modified by adsorbed chitosan. The structure of the chitosan layer on the lowly charged silica was strongly affected by the ionic strength of the solution from which the chitosan adsorption took place. The interactions between SDS and the pre-adsorbed chitosan were found to be similar on lowly charged silica and on highly charged mica.

A novel method based on the Bruggeman effective medium approximation was proposed for the evaluation of ellipsometric data characterizing composite adsorbed layers.

Finally, the effect of the adsorbed layer surface roughness on the QCM-D response in liquid was studied with focus on trapped water. It was found that QCM-D effectively senses water, which is mechanically trapped inside topographical structures with the size in nano-meter scale.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 97 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:54
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-4475 (URN)978-91-7178-739-2 (ISBN)
Public defence
2007-09-14, Salongen, KTH Biblioteket, Osquara backe 31, Stockholm, 09:00
Opponent
Supervisors
Note
QC 20100809Available from: 2009-08-30 Created: 2007-08-30 Last updated: 2010-08-09Bibliographically approved

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