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  • 1.
    Feiler, Adam
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Stiernstedt, Johanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Theander, Katarina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Jenkins, Paul
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Effect of capillary condensation on friction force and adhesion2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 2, p. 517-522Article in journal (Refereed)
    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.

  • 2.
    Theander, Katarina
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Studies of surfactant behaviour and model surfaces relevant to flotation deinking2006Doctoral 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.

  • 3.
    Theander, Katarina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Pugh, R. J.
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Forces and Friction Between Hydrophilic and Hydrophobic Surfaces: Influence of Oleate Species2007In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 313, no 2, p. 735-746Article in journal (Refereed)
    Abstract [en]

     The atomic force microscope has been used to investigate normal surface forces and lateral friction forces at different concentrations of sodium oleate, a frequently used fatty acid in the deinking process. The measurements have been performed using the colloidal probe technique with bead materials consisting of cellulose and silica. Cellulose was used together with a printing ink alkyd resin and mica, whereas silica was used with a hydrophobized silica wafer. The cellulose-alkyd resin system showed stronger double layer repulsion and the friction was reduced with increasing surfactant concentration. The adhesive interaction disappeared immediately on addition of sodium oleate. The normal Surface forces for cellulose-mica indicated no apparent adsorption of the sodium oleate however, the friction coefficient increased on addition of sodium oleate, which we ascribe to some limited adsorption increasing the effective surface roughness. The silica-hydrophobic silica system showed a completely different surface force behavior at the different concentrations. An attractive hydrophobic interaction was evident since the surfaces jumped into adhesive contact at a longer distance than the van der Waals forces would predict. The strong adhesion was reflected in the friction forces as a nonlinear relationship between load and friction and a large friction response at zero applied load. Indirect evidence of adsorption to the hydrophilic silica surface was also observed in this case, and QCM studies were performed to confirm the adsorption of material to both surfaces.

  • 4.
    Theander, Katarina
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Pugh, R. J.
    Rutland, Mark
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Friction force measurements relevant to de-inking by means of atomic force microscope2005In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 291, no 2, p. 361-368Article in journal (Refereed)
    Abstract [en]

    In the pulping step of the de-inking process, the ink detaches from the fibers due to shear and physical chemical interaction. In order to get a better understanding of the forces involved between cellulose and ink, the atomic force microscope and the colloidal probe technique have been used in the presence of a model chemical dispersant (hexa-ethyleneglycol mono n-dodecyl ether, C 12E6). A cellulose bead was used as the colloidal probe and three different lower surfaces have been used, an alkyd resin, mica and a cellulose sphere. The normal and lateral forces have been measured at a range of nonionic concentrations. It was found that the lateral sliding friction forces deceased with increasing surfactant concentration for both the alkyd resin and mica while no differences were observed for the cellulose surface. In addition, only a very small change in normal force could be detected for the alkyd surface as the concentration changed.

  • 5. Theander, Katarina
    et al.
    Pugh, Robert J.
    Synergism and Foaming Properties in Mixed Nonionic/Fatty Acid Surfactant Systems2003In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 267, p. 9-17Article in journal (Refereed)
    Abstract [en]

    The synergism and foaming behavior of a mixed surfactant system consisting of a nonionic surfactant (polyethoxylated alkyl ether CnEm) and a fatty acid soap (sodium oleate) were studied. The micellar interaction parameter (the beta-parameter) was determined from the cmc following the approach of Rubingh's regular solution theory. For both the C12E6/sodium oleate and the C14E6/sodium oleate mixtures, the results indicate a fairly strong attractive interaction (negative beta-values), which were in agreement with previous data reported for other nonionic/anionic surfactant systems. The characteristics of the foam produced from the surfactants were evaluated using a glass column equipped with a series of electrodes measuring the conductance of the foam, which enabled the water content of the foam to be determined. From these measurements. since the total foam volume was almost the same for all concentrations and surfactants, we compared the amount of liquid in the foam produced under dynamic foaming and the ability of the foam to entrain the liquid after the airflow was switched-off (static foam stability). The amount of liquid in the foam 100 s after the air was switched-off followed the order NaOl > C12E6 > C14E6. Also, the mixtures had the same foam volumes as the pure surfactants at the same concentration. However, both mixtures had higher concentrations of liquid in the foam when the mole fraction of the nonionic surfactant in the mixed surfactant system was greater than about >0.3 in the solution.

  • 6. Theander, Katarina
    et al.
    Pugh, Robert J.
    The Influence of pH and Temperature on the Equilibrium and Dynamic Surface Tension of Aqueous Solutions of Sodium Oleate2001In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 239, no 1, p. 209-216Article in journal (Refereed)
    Abstract [en]

    For aqueous solutions of sodium oleate, the dynamic surface tension (using the maximum bubble pressure technique) and the equilibrium surface tensions (using the du Nouy ring method) were studied. Experiments were carried out within the pH range 7 to 13 and at temperatures from 20 to 60 degreesC. From the equilibrium surface tension studies at 25 degreesC, a wide variation in surface activity was found to occur in the premicellar concentration range, depending on pH and oleate concentration, and this was explained on the basis of the formation of strongly surface-active premicellar species. It was also shown that the critical micelle concentration (cmc) of the system increased with pH within the pH range 7-12, Dynamic surface tension experiments were carried out from 20 to 60 degreesC at concentrations beyond the cmc in alkaline solutions, and the adsorption kinetics at the air/solution interface were analyzed using established theoretical diffusion models. From these data, the effective diffusion coefficients (D-eff) for the oleate species were determined and the presence of an interfacial activation barrier in the diffusion process was confirmed. It was found that the D-eff values obtained within the temperature range from 40 to 60 degreesC at 2-3 mM were in general agreement with previously reported values for the oleate dimer obtained by pulse-gradient FT-NMR. Furthermore, D-eff significantly increased with temperature and also increased with concentration at higher temperatures (> 40 degreesC).

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