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A novel technique for the in situ calibration and measurement of friction with the atomic force microscope
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
2005 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 76, no 8, 083710- p.Article in journal (Refereed) Published
Abstract [en]

 Presented here is a novel technique for the in situ calibration and measurement of friction with the atomic force microscope that can be applied simultaneously with the normal force measurement. The method exploits the fact that the cantilever sits at an angle of about 10 degrees to the horizontal, which causes the tip (or probe) to slide horizontally over the substrate as a normal force run is performed. This sliding gives rise to an axial friction force (in the axial direction of the cantilever), which is measured through the difference in the constant compliance slopes of the inward and outward traces. Traditionally, friction is measured through lateral scanning of the substrate, which is time consuming, and requires an ex situ calibration of both the torsional spring constant and the lateral sensitivity of the photodiode detector. The present method requires no calibration other than the normal spring constant and the vertical sensitivity of the detector, which is routinely done in the force analysis. The present protocol can also be applied to preexisting force curves, and, in addition, it provides the means to correct force data for cantilevers with large probes.

Place, publisher, year, edition, pages
2005. Vol. 76, no 8, 083710- p.
Keyword [en]
TORSIONAL SPRING CONSTANT; ADHESION MEASUREMENTS; CANTILEVERS; SURFACTANT; MONOLAYERS; TILT
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-9078DOI: 10.1063/1.2006407ISI: 000231276600035ScopusID: 2-s2.0-26444462128OAI: oai:DiVA.org:kth-9078DiVA: diva2:14635
Note
QC 20100824Available from: 2006-02-10 Created: 2006-02-10 Last updated: 2010-08-24Bibliographically approved
In thesis
1. Interactions of cellulose and model surfaces
Open this publication in new window or tab >>Interactions of cellulose and model surfaces
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The focus of this thesis is fundamental surface force and friction studies of silica and cellulose surfaces, performed mainly with the atomic force microscope (AFM). The normal interactions between model cellulose surfaces have been found to consist of a longer range double layer force with a short range steric interaction, the nature of which is extensively discussed. Both the surface charge and range of the steric force depend on the type of cellulose substrate used, as does the magnitude of the adhesion. Studies of friction on the same surfaces reveal that surface roughness is the determining factor for the friction coefficient, with which it increases monotonically. The absolute value, however, is determined by the surface chemistry.

The above is illustrated by studies of the effect of adsorbed xyloglucan, a prospective paper additive, which is found in the cell wall of all plants. Xyloglucan is like cellulose a poly- saccharide but the effect of its adsorption was to reduce the friction significantly, while following the identical trend with surface roughness. Xyloglucan also increases the adhesion between cellulose surfaces in a time dependent manner, interpreted in terms of a diffusive bridging interaction. These facts combined provide a mechanistic explanation to contemporaneous findings about xyloglucans benefit in paper strength and formation.

In air, the adhesion between e.g. particles or fibres, must be at least partially determined by the formation of capillary condensates. The dependence of capillary condensation on relative humidity is however not yet fully understood so studies have been performed to cast light on this phenomenon. Above about 60 % relative humidity the adhesion and friction increase dramatically due to the formation of large capillary condensates. The extent of the condensates depends both on the time the surfaces equilibrate, but also on the surface roughness. Harvesting of the condensate during shearing is also observed through hysteresis of the friction-load relationship.

Measurements of surface forces and friction in surfactant systems show a clear relation between the adsorbed surfactant layer and the barrier force and adhesion, which in turn determine the friction. All of these interactions are critically dependent on the composition of the surfactant solution. A mixed surfactant system has been studied consisting of a trimethylammonium cationic surfactant and a polyoxyethylene nonionic surfactant. The results are interpreted in terms of current theories of adsorption and synergistic interactions. Finally, a novel technique for the in situ calibration and measurement of friction with the AFM is proposed. Comparison with lateral measurements show that the approach is successful.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 58 p.
Series
Trita-YTK, ISSN 1650-0490 ; 0603
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-619 (URN)91-7178-260-5 (ISBN)
Public defence
2006-02-24, sal F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100920Available from: 2006-02-10 Created: 2006-02-10 Last updated: 2011-12-19Bibliographically approved

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