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Effect of capillary condensation on friction force and adhesion
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
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2007 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 2, 517-522 p.Article in journal (Refereed) Published
Abstract [en]

Friction force measurements have been conducted with a colloid probe on mica and silica (both hydrophilic and hydrophobized) after long (24 h) exposure to high-humidity air. Adhesion and friction measurements have also been performed on cellulose substrates. The long exposure to high humidity led to a large hysteresis between loading and unloading in the friction measurements with separation occurring at large negative applied loads. The large hysteresis in the friction - load relationship is attributed to a contact area hysteresis of the capillary condensate which built up during loading and did not evaporate during the unloading regime. The magnitude of the friction force varied dramatically between substrates and was lowest on the mica substrate and highest on the hydrophilic silica substrate, with the hydrophobized silica and cellulose being intermediate. The adhesion due to capillary forces on cellulose was small compared to that on the other substrates, due to the greater roughness of these surfaces.

Place, publisher, year, edition, pages
2007. Vol. 23, no 2, 517-522 p.
Keyword [en]
Adhesion, Atmospheric humidity, Condensation, Friction, Hysteresis, Mica, Silica, Surface roughness
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-9041DOI: 10.1021/la060456fISI: 000243338500031Scopus ID: 2-s2.0-33846881797OAI: oai:DiVA.org:kth-9041DiVA: diva2:14582
Note
QC 20100909. Uppdaterad från Submitted till Published (20100909)Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Studies of surfactant behaviour and model surfaces relevant to flotation deinking
Open this publication in new window or tab >>Studies of surfactant behaviour and model surfaces relevant to flotation deinking
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The objective of this work was to investigate the behaviour of some model surfactants used in the deinking process, namely, sodium oleate and two ethoxylated nonionic surfactants (C12E6 and C14E6) as well as to investigate the suitability of various model substrates for mimicking interactions in technical systems. The influence of the adsorption to the air � water interface has been measured by means of equilibrium and dynamic surface tension measurements, as well as foaming experiments. It was found that the solution pH and temperature influenced the dynamic and equilibrium surface tensions and the value of the cmc. Equilibrium surface tension measurements were also performed with mixtures of sodium oleate and nonionic surfactants and a strong synergistic effect was obtained, which means that a greater surface tension reduction can be obtained at lower surfactant concentrations. The foaming experiments, carried out with a Foam Scan Apparatus, showed an approximately constant total foam volume for both the pure surfactant systems and for the mixtures. In addition, the foam was slightly more stable for the mixtures than for the pure components.

Friction and surface forces between solid surfaces in liquid were studied using the atomic force microscope (AFM) from which inferences about the adsorption to these interfaces could be drawn. The AFM measurements were performed with the colloidal probe technique using cellulose as colloidal probe and an alkyd resin as a model ink surface. Mica and silica were both used as models for hydrophilic surfaces. Adsorption was observed on the alkyd resin, both with sodium oleate and with C12E6. The adsorption was registered both as a change in normal surface force interaction and as a strong reduction in friction force and friction coefficient at increasing surfactant concentration. The magnitude of the friction force was observed to be dependent on the adhesion and varied monotonically with the surface roughness. Measurements of adhesion and friction forces in air were performed, and the same conclusions about the effect of roughness were drawn. Finally the friction force behaviour appears to be similar if the adhesion is caused by a vapour bridge in liquid, or by a liquid bridge in air, where the formation of a capillary bridge in air is strongly dependent on the relative humidity.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 68 p.
Series
Trita-YTK, ISSN 1650-0490 ; 0601
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-602 (URN)91-7178-259-1 (ISBN)
Public defence
2006-02-10, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100923Available from: 2006-01-27 Created: 2006-01-27 Last updated: 2010-09-23Bibliographically approved
2. 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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