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- Nordgren, Niklas, 1975-, et al.
(author)
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Mediation of the Nanotribological Properties of Cellulose by Chitosan Adsorption
- 2009
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In: Biomacromolecules. - USA : American Chemical Society. - 1525-7797 .- 1526-4602. ; 10:3, s. 645-650
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Journal article (peer-reviewed)abstract
- Cellulosic model surfaces functionalized with chitosan, a naturally occurring cationic biomacromolecule, by in-situ adsorption have been studied with an atomic force microscope (AFM) in colloidal probe configuration. The interaction forces on approach and separation, as well as the nanotribological properties, were shown to be highly pH-dependent and a significant difference in the behaviour was seen before and after chitosan adsorption. In general, all forces on approach showed a highly repulsive interaction at shorter distances due to deformation of the probe. At high pH, before chitosan adsorption, a long-range electrostatic repulsion was observed, consistent with DLVO theory. However at low pH no electrostatic contribution was found before adsorption probably due to charge neutralization of carboxyl groups. After chitosan adsorption, repulsive forces acting over a much longer distance than predicted by DLVO theory were present at low pH. This effect was ascribed to chain extension of the chitosan species of which the magnitude and the range of the force increased dramatically with higher charge at low pH. In all cases, a typical saw-tooth patterned adhesion was present with pull-off events occurring at different separations. The frequency of these events after chitosan adsorption was greatly increased at longer distances. Additionally, the adsorbed chitosan markedly reduced the friction where the largest effect was a 7-fold decrease of the friction coefficient observed at low pH.
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| 2. |
- Sundman, Ola, 1979-
(author)
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Cation adsorption properties of substituted kraft fibres : an experimental and thermodynamic modelling study
- 2008
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Doctoral thesis (other academic/artistic)abstract
- Acid/base and metal ion adsorption properties have been investigated for a range of chemically modified bleached Kraft fibre materials (pulps). The studies were performed via potentiometric titrations, Flame Atomic Absorbtion (and Emission) Spectroscopy, Inductively Coupled Plasma Optical Emission Spectroscopy and Extended X-ray Absorbtion Fine Structure measurements. As a result of a chemical modification procedure, the total concentration of acidic carboxylate groups in the fibre materials ranged between 43 and 590 μmol/g. The preferable surface potential model for modelling the ionic strength dependent acid/base properties of fibre materials with low charge densities, i.e. unmodified fully bleached Kraft fibre materials, was found to be the Basic Stern Model. For fibre materials with high total charge, ≳100 μmol/g, this model resulted in poor fits to data, and for such materials a number of Constant Capacitance Models, one at each ionic strength, must be recommended. With respect to metal ion adsorption, the results have indicated that the unspecific Donnan theory could correctly model the simultaneous adsorption of several metal ions, i.e. K+, Na+, Mg2+, Ca2+ and Cu2+, provided that the salt concentration in the fibre suspension is low. In suspensions of high salt concentration it was, however, found that this very same model strongly underestimated the adsorption of Ca2+ and Cu2+. Here, the Donnan model had to be complemented by specific ion exchange equilibria. These results were corroborated by spectroscopic evidence of specific interactions between Cu2+-ions and fibres. The spectroscopic indication of a complex formed between two fibre surface carboxylate groups and one Cu2+-ion, agree with the specific ion exchange model. It was therefore concluded that specific metal ionfibre interactions cannot be neglected, especially at high salt concentrations. The interactions occurring between the polycation GaO4Al12(OH)24(H2O)127+ and fibre materials were studied by both adsorption and spectroscopic measurements. These indicate that GaO4Al12(OH)24(H2O)127+ is surprisingly stable in fibre suspensions and that intact GaO4Al12(OH)24(H2O)127+- ions are strongly adsorbed onto the fibres. Also for this ion, specific interactions has to be considered, since the strong adsorption registered was too strong to be explained by Donnan equilibria. In the thesis, the stochiometric composition and an equilibrium constant characterising these interactions is presented.
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| 3. |
- Virtanen, Kirsi A, et al.
(author)
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Functional brown adipose tissue in healthy adults.
- 2009
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In: The New England journal of medicine. - 1533-4406. ; 360:15, s. 1518-25
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Journal article (peer-reviewed)abstract
- Using positron-emission tomography (PET), we found that cold-induced glucose uptake was increased by a factor of 15 in paracervical and supraclavicular adipose tissue in five healthy subjects. We obtained biopsy specimens of this tissue from the first three consecutive subjects and documented messenger RNA (mRNA) and protein levels of the brown-adipocyte marker, uncoupling protein 1 (UCP1). Together with morphologic assessment, which showed numerous multilocular, intracellular lipid droplets, and with the results of biochemical analysis, these findings document the presence of substantial amounts of metabolically active brown adipose tissue in healthy adult humans.
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| 4. |
- Wallqvist, Viveca, 1977-
(author)
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Interactions between non-polar surfaces in water: Fokus on talc, pitch and surface roughness effects
- 2009
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Doctoral thesis (other academic/artistic)abstract
- The aim of this thesis work was to gain understanding of the interactions between talc mineral and surfaces, liquids and chemicals relevant for industrial applications, such as pulp and paper. Talc is used in the pulp and paper industry as a filler pigment, in control of pitch (lipophilic extractives) deposits and as a coating pigment. A deeper understanding of talc interactions will be beneficial in optimizing its use. Long-range attractive interactions between talc and hydrophobic model probes, as well as pitch probes, have been measured using the atomic force microscope (AFM) colloidal probe method. Two procedures for preparation of pitch colloidal probes were developed to allow these studies. Model hydrophobic, nanorough surfaces with surface energy characteristics similar to talc have also been prepared and their interactions with hydrophobic model probes compared to interactions between hydrophobic model probes and talc. It is demonstrated that talc mineral interacts with model hydrophobic particles, as well as with pitch, by long-range attractive forces, considerably stronger than the expected van der Waals force. The possible origin of the measured interaction forces is discussed, and the conclusion is that the main cause is an attractive capillary force due to formation of a gas/vapor capillary between the surfaces. Force measurements using model hydrophobic, nanorough surfaces show that a large-scale waviness does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. It is demonstrated that a large variation in adhesion force corresponds to a small variation in local contact angle of the capillaries at the surfaces. The nature of the surface topographical features influences the capillary attraction by affecting the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on the size of the surface features and whether they exist in the form of crevices or as extending ridges. Entrapment of air also affects the imbibition of water in pressed talc tablets. The effects of wetting and dispersion agents on the interactions between talc and hydrophobic probes have also been investigated. It is demonstrated that a common dispersing agent used for talc, poly(acrylic acid), does not affect the capillary attraction between talc and non-polar probes. In fact, the results strongly suggest that poly(acrylic acid) does not adsorb on the basal plane of talc. From this finding it is inferred that the stabilizing effect of this additive most likely is due to adsorption to the edges of talc. In contrast, a wetting agent (the non-ionic triblock copolymer Pluronic PE6400) removes the long-range capillary attraction. It is suggested that such an ability to replace air at the talc surface is of great importance for an efficient wetting agent. The Hamaker constant for talc has also been estimated by using optical data obtained from spectroscopic ellipsometry. It is demonstrated that a nanocrystalline talc mineral, cut in different directions displays very small differences in Hamaker constant between the different crystallographic orientations, whereas a microcrystalline sample displays a significantly higher value. The estimated Hamaker constants are discussed for different material combinations of relevance for the pulp- and paper industry, such as cellulose and calcium carbonate.
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