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  • 1.
    Boily, J F
    et al.
    Umeå Universitet.
    Nilsson, Nils
    Umeå Universitet.
    Persson, Per
    Umeå Universitet.
    Sjöberg, Staffan
    Umeå Universitet.
    Benzenecarboxylate surface complexation at the goethite (alpha-FeOOH)/water interface: I. A mechanistic description of pyromellitate surface complexes from the combined evidence of infrared spectroscopy, potentiometry, adsorption data, and surface complexation modeling2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, no 13, p. 5719-5729Article in journal (Refereed)
    Abstract [en]

    An investigation combining IR spectroscopy, potentiometric titrations, and adsorption experiments was carried out to study pyromellitate (1,2,4,5-benzenetetracarboxylate) sorption at the goethite (α-FeOOH)/water interface. The IR spectra show evidence of outer-sphere complexation throughout the pH range from 3 to 9. Below pH 6 additional IR spectroscopic features appear, which are tentatively assigned to inner-sphere complexes. A normalized IR peak area plot for each peak indicative of inner- and of outer-sphere complexes as a function of pH provided a semiquantitative surface speciation scheme. This scheme was successfully reproduced using surface complexation theory with a multisite complexation model calibrated on potentiometric titration and on adsorption data. The surface speciation was described with a binuclear outer-sphere complex on the {110} plane of goethite and a mononuclear inner-sphere complex on the {001} plane. Furthermore, as the IR spectra also indicated partial protonation of pyromellitate complexes at low pH, a partially protonated outer-sphere species on the {110} plane was included in the model.

  • 2.
    Bydén Sjöbom, Malin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Lindström, Birger
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    BinaBinary Phase Equilibria and Structure of the Two α-Methyl-Substituted Surfactants Sodium (R)-2-Methyldecanoate and Racemic Sodium 2-Methyldecanoate ry Phase Exuilibria and Structure of the Chiral α-Methylsubstituted Surfactants Sodium (R)-2-Methyldecanoate and Racemic Sodium 2-Methyldecanoate1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, no 8, p. 2654-2660Article in journal (Refereed)
    Abstract [en]

    In this study, we present the binary phase diagrams for the aqueous systems of the alkyldecanoic salts racemic sodium 2-methyldecanoate and sodium (R)-2-methyldecanoate, respectively. Both systems form a micellar solution phase, as well as a normal hexagonal, a cubic, and a lamellar liquid crystalline phase. They also form a very narrow intermediate phase, situated between the hexagonal and cubic liquid crystalline phases. The methods used for characterization were crossed polaroids, polarizing optical microscope and 2H NMR quadrupolar splittings combined with SAXS studies. The cubic phase gave a well-resolved SAXS diffraction pattern, with eight peaks present, which establishes the bicontinuous cubic structure as Ia3d. A significant difference in these two phase diagrams, compared to those of unsubstituted alkanoates with the same chain length, is the very low Krafft boundary.

  • 3.
    Edlund, Håkan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Khan, A
    La Mesa, C
    Formation of a Liquid Crystalline Phase in the Sodium Taurodeoxycholate-Water System1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 3691-3697Article in journal (Refereed)
    Abstract [en]

    The binary phase equilibria for the system sodium taurodeoxycholate-water have been studied. The system forms a liquid crystalline phase in addition to the previously known isotropic solution phase at 22 °C. 2H (water) NMR quadrupole splitting, SAXS data in combination with the polarizing microscopic texture observed for the liquid crystal indicate that the liquid crystalline phase consists of a hexagonal-type aggregate structure. A metastable liquid crystal, probably with lamellar-type structure, also appears to exist prior to the formation of the stable hexagonal phase. A micellar growth is measured with the NMR self-diffusion method for the isotropic solution phase. Electrical conductance experiments are used to determine the liquid crystal-solution thermal transition.

  • 4.
    Edlund, Håkan
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Sadaghiani, Alireza
    Khan, Ali
    Phase Behaviour and Phase Structure for Catanionic Surfactant Mixtures: DoTAC-SN-Water System1997In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, p. 4953-4963Article in journal (Refereed)
    Abstract [en]

    The phase behavior and phase structure of catanionic surfactant mixtures of DoTAC (dodecyltrimethylammonium chloride) and SN (sodium nonanoate) with water are studied by combined 2H NMR, SAXS, and microscopy techniques at 40 °C. The system forms a large isotropic micellar solution phase with excess water. As the concentration of total surfactant is increased, the solution phase coexists with different liquid crystalline phasesa lamellar phase at equimolar ratio of the two surfactants and hexagonal phases with excess DoTAC and excess SN. The lamellar and hexagonal liquid crystalline phases formed by the binary DoTAC system extensively swell with water on adding the anionic surfactant, and the swelling is more dramatic for the lamellar phase which extends to an equimolar ratio of the two surfactants. The mesophase of the short alkyl chain is incapable of solubilizing any substantial amounts of the long chain DoTAC molecules. SAXS data shows a decrease in bilayer thickness and an unchanged average area per polar group on adding SN into the lamellar phase. For the DoTAC-rich hexagonal phase, the diameter of the cylinder remains unchanged and the average area per polar headgroup is decreased in catanionic mixtures. The 2H NMR quadrupolar splitting values in the hexagonal liquid crystalline phase indicate that the polar headgroups are less extensively hydrated in catanionic mixtures compared to the hydration of the headgroups in the single surfactant systems. The 2H splitting value in the lamellar phase first decreases, going through a zero splitting value, and then the splitting increases again on a continuous decreasing of the total surfactant concentrations. Alkyl chain asymmetry is found to play a dominant role in the formation and stability of aggregates in catanionic surfactant mixtures.

  • 5.
    Fält, Susanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Vesterlind, Eva-Lotta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Swellling of model films of cellulose having different charge densities and comparison to the swelling behavior of corresponding fibers2003In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, no 19, p. 7895-7903Article in journal (Refereed)
    Abstract [en]

    Cellulose model films with different charge densities were prepared by spin-coating dissolved cellulose in N-methylmorpholine-N-oxide onto SiO2 surfaces. The swelling of the model cellulose films due to exposure to solutions of different electrolytes and at different ionic strengths and pH values were studied using QCM-D (quartz crystal microbalance with dissipation monitoring). Results show that at pH 5, there is a swelling of the film at a low electrolyte concentration (10(-4)-10(-2) M), whereas the deswelling of the film was observed at a high electrolyte concentration (10(-1)-1 M). A considerable swelling of the films is seen when they are treated with deionized water with an increasing pH. The swelling of the films is accompanied by an increase in dissipation, that is, a softening of the material, and the deswelling by a decrease in dissipation, that is, a stiffening of the material. Furthermore, exposure of the films to solutions of different electrolytes affected the swelling of the layer. In this respect, the swelling response of Na2SO4 differs from that of NaCl and CaC1(2) by showing simultaneously high swelling and low dissipation values. The results also show that the rate of swelling reaches its lowest value as the electrolyte concentration reaches the detected limit for the deswelling. The QCM-D results are compared to the swelling of the corresponding carboxymethylated fibers, where a similar behavior was found. However, for the fibers a marked deswelling occurred at a high electrolyte concentration, but only a minor deswelling of the cellulose film was observed. This difference between the materials can be ascribed to noncovalent bonds within the film that will not reform when the swelling forces are decreased at high electrolyte concentrations. A direct measurement of the thickness changes was performed using atomic force microscopy, which shows that the change in frequency measured with QCM-D for the films treated with different NaCl electrolyte concentrations corresponds to changes of 1-2%.

  • 6.
    Karlsson, S.
    et al.
    Department of Physical Chemistry, Åbo Akademi University, Porthaninkatu 3-5, FI-20500 Turku, Finland.
    Friman, R.
    Department of Physical Chemistry, Åbo Akademi University, Porthaninkatu 3-5, FI-20500 Turku, Finland.
    Björkqvist, M.
    Laboratory of Industrial Physics, Department of Physics, University of Turku, FI-20014 Turku, Finland.
    Lindström, Birger
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Backlund, S.
    Department of Physical Chemistry, Åbo Akademi University, Porthaninkatu 3-5, FI-20500 Turku, Finland.
    Phase behavior and characterization of the system acetic acid-dodecylamine-water2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 12, p. 3573-3578Article in journal (Refereed)
    Abstract [en]

    The phase behavior of carboxylic acid/alkylamine mixtures in water is largely dictated by a proton transfer from the acid to the amine, which will lead to charged species. If the distribution of carbon atoms is unequal between the acid and the amine, the result will be an ionic surfactant with an organic counterion. In this work the phase diagram for the ternary system acetic acid-dodecylamine-water at 298.2 K has been determined. Dodecylamine forms a lamellar phase with water, but when,acetic acid is added up to an equimolecular ratio between acid and amine, three new phases appear. These phases are an isotropic solution phase, a hexagonal liquid crystalline phase, and a cubic liquid crystalline phase. These three phases are not able to incorporate any excess amine. The solution phase shows the existence of micelles, which are spherical at high dilution, but show an elongation close to the phase border to the hexagonal phase.

  • 7. Marques, Eduardo F.
    et al.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    La Mesa, Camilo
    Khan, Ali
    Liquid Crystals and Phase Equilibria Binary Bile Salt-Water Systems2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, no 11, p. 5178-5186Article in journal (Refereed)
    Abstract [en]

    The phase behavior of several binary sodium bile salt-water systems is investigated over the entire concentration range, with emphasis on concentrated regions beyond the isotropic solution phase. The studied bile acid salts comprise the free salt sodium deoxycholate (SDC), the taurine conjugates sodium taurocholate (STC), sodium taurodeoxycholate (STDC), and sodium taurochenodeoxycholate (STCDC) and the glycine conjugate sodium glycodeoxycholate (SGDC). A combination of classical techniques is used, including phase diagram determination, polarizing microscopy, 2H NMR, and small-angle X-ray scattering (SAXS). The aggregation behavior in the isotropic micellar solutions of STC and STDC is also investigated by pulsed-field gradient NMR self-diffusion. The optical textures and the data from SAXS and 2H NMR clearly point to the formation of hexagonal liquid crystals, possibly of the reverse type, beyond the micellar solution for all the bile salts. Several unusual kinetic effects, such as very slow equilibration times and the formation of transient spherulitic crystals in biphasic regions, are observed. The phase diagrams and structural data are qualitatively discussed in terms of the molecular structure and solubility of the different salts. The formation of lyotropic liquid crystals by bile salts, which has remained unknown for decades, is clearly demonstrated in this work.

  • 8.
    Norgren, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Aggregation of Lignin Derivatives under Alkaline Conditions. Kinetics and Aggregate Structure2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 7, p. 2859-2865Article in journal (Refereed)
    Abstract [en]

    The kinetics of kraft lignin (KL) aggregation at alkaline conditions was studied by quasi-elastic light scattering (QELS) and turbidity measurements. Stability ratios (W) for KL were obtained at 70 °C and various concentrations of sodium chloride. By analyzing the early-time evolution data of aggregate growth obtained from QELS, fractal dimensions of flocs formed in both reaction-limited cluster-cluster aggregation regimes and diffusion-limited cluster-cluster aggregation regimes were determined. Correlations between the fractal dimension and the W-ratio were found in accordance to recent studies of a system containing monodisperse polystyrene colloids. By cryogenic transmission electron microscopy, the fractality of KL aggregate structures in the system was also shown. It was seen from stability studies of KL solutions that the effects of specific co- and counterions follow the Hofmeister series. From the outcome of the investigation, different modes of aggregation occurring in a KL system are proposed. Starting from the macromolecular state of KL and evolving through larger aggregates, the KL clusters finally exhibit a supramolecular structure similar to what earlier has been proposed for native softwood lignin.

  • 9.
    Norgren, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Gärdlund, Linda
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Notley, S. M.
    Australian National University, Canberra, Australia.
    Htun, Myat
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Wågberg, Lars
    Royal Institute of Technology, Stockholm.
    Smooth model surfaces from lignin derivatives: II. Adsorption of polyelectrolytes and PECs monitored by QCM-D2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 7, p. 3737-3743Article in journal (Refereed)
    Abstract [en]

    For the first time, well-defined and stable lignin model surfaces have been utilised as substrates in polyelectrolyte adsorption studies. The adsorption of polyallylamine (PAH), polyacrylic acid (PAA), and polyelectrolyte complexes (PECs) was monitored using quartz crystal microgravimetry with dissipation (QCM-D). The PECs were prepared by mixing PAH and PAA at different ratios and sequences, creating both cationic and anionic PECs with various charge levels. The adsorption experiments were performed in 1 and 10 mM sodium chloride solutions at pH 5 and 7.5. The highest adsorption of PAH and cationic PECs was found at pH 7.5, where the slightly negative charged nature of the lignin substrate is more pronounced, governing electrostatic attraction of oppositely charged polymeric substances. An increase in the adsorption was further found when the electrolyte concentration was increased. In comparison, both PAA and the anionic PEC showed remarkably high adsorption to the lignin model film. The adsorption of PAA was further studied on silica and was found to be relatively low even at high electrolyte concentrations. This indicated that the high PAA adsorption on the lignin films was not induced by a decreased solubility of the anionic polyelectrolyte. The high levels of adsorption on lignin model surfaces found both for PAA and the anionic PAA-PAH polyelectrolyte complex, points to the presence of strong non-ionic interactions in these systems.

  • 10.
    Norgren, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Notley, S. M.
    Department of Applied Mathematics, Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australia.
    Majtnerova, A.
    Department of Fiber and Polymer Technology, Royal Institute of Technology, Stockholm.
    Gellerstedt, G.
    Department of Fiber and Polymer Technology, Royal Institute of Technology, Stockholm.
    Smooth model surfaces from lignin derivatives: I. Preparation and characterization2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 3, p. 1209-1214Article in journal (Refereed)
    Abstract [en]

    Lignin model surfaces were prepared from aqueous alkaline solutions by spin-coating on silica wafers. Films of thicknesses between 20 and 140 nm were easily made by variations in the spinning rate or in the lignin concentration. The roughnesses of the lignin surfaces were relatively low, approximately 1.1 nm (rms) on an area of 25 μm2, as determined by atomic force microscopy imaging. The stability of the lignin films in aqueous solutions was found to be excellent. No changes in the thickness of model surfaces immersed in slightly alkaline solutions (pH 9.2) could be detected even after 5 h soaking. A 10 percent reduction in the thickness of the lignin film was observed after 5 h of exposure to a solution containing 0. M NaCl. This novel preparation method opens great possibilities for further fundamental studies, where interactions between lignin and other substances are of interest to investigate.

  • 11.
    Norgren, Magnus
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Notley, Shannon
    Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University. Canberra 0200 ACT, Australia.
    Surface energy and wettability of spin-coated thin films of lignin isolated from wood.2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 8, p. 5484-5490Article in journal (Refereed)
    Abstract [en]

    The surface energy of lignin films spin-coated onto oxidised silicon wafer has been determined from contact angle measurements of different test liquids with varying polar and dispersive components. Three different lignin raw materials were used, a kraft lignin from softwood along with milled wood lignin from softwood and hardwood. Infrared spectroscopy was used to identify any major functional group differences between the lignin samples. No significant difference in the total solid-vapour surface energy for the different lignin films was observed however the polar component for the kraft lignin was much greater than for either of the milled wood lignin samples consistent with the presence of carboxyl groups. Furthermore, the total surface energy of lignin of 53-56 mJm-2 is of a similar magnitude to cellulose, also found in the wood cell wall however cellulose has a higher polar component leading to a lower contact angle with water and greater wettability than the milled wood lignin. Although lignin is not hydrophobic according to the strictest definition of a water contact angle of greater than 90°, water may only be considered a partially wetting liquid on a lignin surface. This supports the long-held belief that one of the functions of lignin in the wood cell wall is to provide water-proofing to aid in water transport. Furthermore, these results on the solid-vapour surface energy of lignin will provide invaluable insight for many natural and industrial applications including in the design and manufacture of many sustainable products such as paper, fibreboard and polymer composite blends.

  • 12.
    Notley, Shannon
    et al.
    Australian National University, Canberra, Australia.
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Measurement of interaction forces between lignin and cellulose as a function of aqueous electrolyte solution conditions.2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 26, p. 11199-11204Article in journal (Refereed)
    Abstract [en]

    The interaction between a lignin film and cellulose sphere has been measured using the colloidal probe force technique as a function of aqueous electrolyte solution conditions. The lignin film was first studied for its roughness and stability using atomic force microscopy imaging and quartz crystal microbalance measurements respectively. The film was found to be smooth and stable in the pH range of 3.5 to 9 and in ionic strengths up to and including 0.01 M. This range of ionic strength and pH was hence used to measure the surface forces profiles between lignin and cellulose. Under these solution conditions, the measured forces behaved according to DLVO theory. The force-distance curves could be fitted between the limits of constant charge and constant potential and the surface potential of the lignin films was determined as a function of pH. At pH greater than 9.5, a short range steric repulsion was observed indicating that the film was swelling to a large extent but did not dissolve. Thus, lignin films prepared in this manner are suitable for a range of surface forces studies.

  • 13.
    Persson, Gerd
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hedenström, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Lindblom, Göran
    Phase Behavior of 1-Alkylpyridinium Octane-1-sulfonates: Effect of the 1-Alkylpyridinium Counterion Size2004In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, no 4, p. 1168-1179Article in journal (Refereed)
    Abstract [en]

    The temperature-versus-composition phase diagrams of eight different 1-alkylpyridinium octane-1-sulfonates (APOSs) in water were studied by 1H NMR, 2H NMR, pulsed gradient spin-echo NMR, small-angle X-ray diffraction, differential scanning calorimetry, surface tension and conductivity measurements, and polarizing microscopy. The number of carbons (nc) in the hydrocarbon chain of the pyridinium counterions was varied from nc = 1 to nc = 8 to study how the phase behavior of the APOS/2H2O systems was affected by a change in the chain length of the counterion. The sodium octane-1-sulfonate (NaOS)/water system was used as a reference. This system formed an isotropic micellar solution (L1) phase and a normal hexagonal (HI) phase. All APOSs were readily soluble in water and formed L1 phases. The surface tension above the critical micelle concentration for nc between 1 and 3 was higher than that for NaOS, and it decreased steadily for the different APOSs with increasing chain length. The area per molecule at the air/solution interfaces was rather constant at 68 Å2 for nc between 1 and 7. For 1-octylpyridinium octane-1-sulfonate (OPOS), it was about 5 Å2 smaller, which was just outside the estimated error. However, the smallest area was obtained for NaOS. At higher surfactant concentrations, liquid crystalline phases formed. Both cubic and HI phases were found for nc = 1 and 2, while for nc between 3 and 5 only an HI phase was observed. HI and lamellar liquid crystalline (L) phases formed for nc = 6 and 7. The only liquid crystalline phase found in the OPOS system was a L phase. The NaOS HI phase was the only liquid crystalline phase that showed a linear relation between the 2H2O NMR quadrupolar splitting (W) and Xsurf/XW, where Xsurf and XW are the mole fractions of surfactant and water. The OPOS lamellae were found to be much thinner than expected, indicating a defect lamellar structure. This was further supported by the behavior of the quadrupolar splitting of deuterated OPOS. The anomalous behaviors of the 2H2O NMR quadrupolar splitting observed in the L phases of 1-heptylpyridinium octane-1-sulfonate and OPOS were interpreted in terms of changes in the population of the water molecules residing in different sites combined with a continuous rearrangement of the lamellae surface with the possible development of holes. The appearances of the phase diagrams were discussed in terms of surfactant molecular geometry and the packing of the amphiphiles in the aggregates formed.

  • 14.
    Svanedal, Ida
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Andersson, Fredrik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Hedenström, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Satija, Sushil K.
    NIST, Ctr Neutron Res, 100 Bur Dr,MS 6100, Gaithersburg, MD 20899 USA.
    Lindman, Björn
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering. Univ Coimbra, Dept Chem, Rua Larga, P-3004535 Coimbra, Portugal.
    Rennie, Adrian R.
    Uppsala Univ, Mat Phys, Uppsala, Sweden; Uppsala Univ, Ctr Neutron Scattering, Angstrom Lab, Uppsala, Sweden.
    Molecular Organization of an Adsorbed Layer: A Zwitterionic, pH-Sensitive Surfactant at the Air/Water Interface2016In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 42, p. 10936-10945Article in journal (Refereed)
    Abstract [en]

    Neutron and X-ray reflection measurements have been used to study the structure of the adsorbed layer of a chelating surfactant at the air/liquid interface. The chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (C-12-DTPA) has a large headgroup containing eight donor atoms that can participate in the coordination of metal ions. The donor atoms are also titrating, resulting in an amphoteric surfactant that can adopt a number of differently charged species depending on the pH. Very strong coordination complexes are formed with metal ions, where the metal ion can be considered as part of the surfactant structure, in contrast to monovalent cations that act as regular counterions to the negative net charge. Adsorption was investigated over a large concentration interval, from well below the critical micelle concentration (cmc) to five times the cmc. The most striking result is the maximum in the surface excess found around the cmc, winch is consistent with previous indications from surface tension measurements. Adding divalent metal ions has a limited effect on the adsorption at the air/liquid interface. The reason is the coordination of the metal ion, resulting in compensating deprotonation of the complex. Small variations in the headgroup area of different metal complexes are found, correlating to the conditional stability constants. Adding sodium chloride has a significant effect on the adsorption behavior, and the results indicate that the protonation equilibrium is more important than the ionic strength effects. From combined fits of the neutron and X-ray data, a model that consists of a thick headgroup region and a relatively thin dehydrated tail region is found, and it indicates that the tails are not fully extended and that the limiting area per molecule is determined by the bulky headgroup.

  • 15.
    Svanedal, Ida
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Boija, Susanne
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Almesåker, Ann
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Persson, Gerd
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Andersson, Fredrik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Hedenström, Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Bylund, Dan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Metal Ion Coordination, Conditional Stability Constants and Solution Behavior of Chelating Surfactant Metal Complexes2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 16, p. 4605-4612Article in journal (Refereed)
    Abstract [en]

    Coordination complexes of some divalent metal ions with the DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) have been examined in terms of chelation and solution behavior. The headgroup of 4-C 12-DTPA contains eight donor atoms that can participate in the coordination of a metal ion. Conditional stability constants for five transition metal complexes with 4-C12-DTPA were determined by competition measurements between 4-C12-DTPA and DTPA, using electrospray ionization mass spectrometry (ESI-MS). Small differences in the relative strength between the coordination complexes of DTPA and 4-C12-DTPA indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. The coordination of Cu2+ ions was investigated in particular, using UV-visible spectroscopy. By constructing Job's plots, it was found that 4-C12-DTPA could coordinate up to two Cu2+ ions. Surface tension measurements and NMR diffusometry showed that the coordination of metal ions affected the solution behavior of 4-C 12-DTPA, but there were no specific trends between the studied divalent metal complexes. Generally, the effects of the metal ion coordination could be linked to the neutralization of the headgroup charge of 4-C 12-DTPA, and the resulting reduced electrostatic repulsions between adjacent surfactants in micelles and monolayers. The pH vs concentration plots, on the other hand, showed a distinct difference between 4-C12-DTPA complexes of the alkaline earth metals and the transition metals. This was explained by the difference in coordination between the two groups of metal ions, as predicted by the hard and soft acid and base (HSAB) theory.

  • 16.
    Svanedal, Ida
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Boija, Susanne
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Headgroup interactions and ion flotation efficiency in mixtures of a chelating surfactant, different foaming agents and divalent metal ions2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 22, p. 6331-6338Article in journal (Refereed)
    Abstract [en]

    The correlation between interaction parameters and ion flotation efficiency in mixtures of chelating surfactant metal complexes and different foaming agents was investigated. We have recently shown that chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C-12-DTPA) forms strong coordination complexes with divalent metal ions, and this can be utilized in ion flotation. Interaction parameters for mixed micelles and mixed monolayer formation for Mg2+ and Ni2+ complexes with the chelating surfactant 4-C-12-DTPA and different foaming agents were calculated by Rubingh's regular solution theory. Parameters for the calculations were extracted from surface tension measurements and NMR diffusometry. The effects of metal ion coordination on the interactions between 4-C-12-DTPA and the foaming agents could be linked to a previously established difference in coordination chemistry between the examined metal ions. As can be expected from mixtures of amphoteric surfactants, the interactions were strongly pH-dependent. Strong correlation was found between interaction parameter beta(sigma)for mixed monolayer formation and the phase-transfer efficiency of Ni2+ complexes with 4-C-12-DTPA during flotation in a customized flotation cell. In a mixture of Cu(2+)and Zn2+, the significant difference in conditional stability constants (log K) between the metal complexes was utilized to selectively recover the metal complex with the highest log K (Cu2+) by ion flotation. Flotation experiments in an excess concentration of metal ions confirmed the coordination of more than one metal ion to the headgroup of 4-C-12-DTPA.

  • 17.
    Svanedal, Ida
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Persson, Gerd
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Anomalies in Solution Behavior of an Alkyl Aminopolycarboxylic Chelating Surfactant2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 45, p. 13708-13716Article in journal (Refereed)
    Abstract [en]

    The solution behavior of a DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant, 4-C12-DTPA, has beenstudied by tensiometry and NMR diffusometry. In the absence of metalions, the eight donor atoms in the headgroup are titrating, and thecharge of the headgroup can thus be tuned by altering the pH. 4-C12-DTPA changes from cationic at very low pH, over a number ofzwitterionic species as the pH is increased, and eventually becomesanionic at high pH. Around the isoelectric point, the chelatingsurfactant precipitated. The solution properties, studied above thesolubility gap, were found strongly pH dependent. When increasing theamount of negative charges in the headgroup, by increasing the pH, theadsorption efficiency was reduced and the cmc was increased. Anoptimum in surface tension reduction was found at pH 5, due to aproper balance between protonated and dissociated groups. Anomaliesbetween surface tension measurements and NMR diffusometry in determination of cmc revealed a more complex relationbetween surface tension, surface coverage, and cmc than usually considered, which is not in line with the common interpretationof the Gibbs adsorption equation. At some of the investigated pH levels, measurements of bulk pH could confirm the location ofcmc, due to the increased protonation of micelles compared to monomers in solution. The adsorption of monomers to the air−water interface showed unusually slow time dependence, evident from decreasing surface tension for several hours. This isexplained by rearrangements of the large head groups to reduce the headgroup area and increase the packing parameter.

  • 18.
    Svanedal, Ida
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Persson, Gerd
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Edlund, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Chemical Engineering.
    Interactions in Mixed Micellar Systems of an Amphoteric Chelating Surfactant and Ionic Surfactants2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 5, p. 1250-1256Article in journal (Refereed)
    Abstract [en]

    Mixtures of ionic surfactants and the chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (4-C12-DTPA) have been examined in terms of interactions in mixed micellar systems. The amphoteric 4-C12-DTPA is zwitterionic with a negative net charge at the studied pH levels. The investigated ionic surfactants were the cationic dodecyltrimethylammonium chloride (DoTAC), the anionic sodium dodecyl sulfate (SDS), and the zwitterionic dimethyldodecylamine-N-oxide (DDAO). The surfactants all have the same hydrophobic chain lengths, and the results are evaluated in terms of headgroup interactions. 4-C12-DTPA interacts with different ionic surfactants by accepting or donating protons to the aqueous solution to increase the attractive interactions between the two surfactants; i.e., the protonation equilibrium of 4-C12-DTPA is shifted in different directions depending on whether there are predominant repulsions between positively or negatively charged groups in the mixed micelles. This was monitored by measuring pH vs concentration in the mixed systems. By measuring the pH, it was also possible to study the shift in the protonation equilibrium at increasing concentration, as the composition in the micelles approaches the composition in the total solution. Following the approach of Rubingh's regular solution theory, the interaction parameter β for mixed micelle formation was calculated from the cmc values determined by NMR diffusometry. Synergism in mixed micelle formation and negative β parameters were found in all of the investigated systems. As expected, the most negative β parameter was found in the mixture with DoTAC, followed by DDAO and SDS. The self-diffusion in the 4-C12-DTPA/DoTAC system was also discussed. The self-diffusion coefficient vs concentration plots show two distinctly different curves, depending on the surfactant that is present in excess.

  • 19. Wågberg, Lars
    et al.
    Decher, Gero
    Norgren, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Lindström, Tom
    Ankerfors, Mikael
    Axnäs, Karl
    The build-up of polyelectrolyte multilayers of microfibrillated cellulose and cationic polyelectrolytes2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 3, p. 784-795Article in journal (Refereed)
    Abstract [en]

    A new type of nanocellulosic material has been prepared by high-pressure homogenization of carboxymethylated cellulose fibers followed by ultrasonication and centrifugation. This material had a cylindrical cross-section as shown by transmission electron microscopy with a diameter of 5-15 nm and a length of up to 1 mu m. Calculations, using the Poisson-Boltzmann equation, showed that the surface potential was between 200 and 250 mV, depending on the pH, the salt concentration, and the size of the fibrils. They also showed that the carboxyl groups on the surface of the nanofibrils are not fully dissociated until the pH has reached pH = similar to 10 in deionized water. Calculations of the interaction between the fibrils using the Derjaguin-Landau-Verwey-Overbeek theory and assuming a cylindrical geometry indicated that there is a large electrostatic repulsion between these fibrils, provided the carboxyl groups are dissociated. If the pH is too low and/or the salt concentration is too high, there will be a large attraction between the fibrils, leading to a rapid aggregation of the fibrils. It is also possible to form polyelectrolyte multilayers (PEMs) by combining different types of polyelectrolytes and microfibrillated cellulose (MFC). In this study, silicon oxide surfaces were first treated with cationic polyelectrolytes before the surfaces were exposed to MFC. The build-up of the layers was monitored with ellipsometry, and they show that it is possible to form very well-defined layers by combinations of MFC and different types of polyelectrolytes and different ionic strengths of the solutions during the adsorption of the polyelectrolyte. A polyelectrolyte with a three-dimensional structure leads to the build-up of thick layers of MFC, whereas the use of a highly charged linear polyelectrolyte leads to the formation of thinner layers of MFC. An increase in the salt concentration during the adsorption of the polyelectrolyte results in the formation of thicker layers of MFC, indicating that the structure of the adsorbed polyelectrolyte has a large influence on the formation of the MFC layer. The films of polyelectrolytes and MFC were so smooth and well-defined that they showed clearly different interference colors, depending on the film thickness. A comparison between the thickness of the films, as measured with ellipsometry, and the thickness estimated from their colors showed good agreement, assuming that the films consisted mainly of solid cellulose with a refractive index of 1.53. Carboxymethylated MFC is thus a new type of nanomaterial that can be combined with oppositely charged polyelectrolytes to form well-defined layers that may be used to form, for example, new types of sensor materials.

  • 20.
    Wågberg, Lars
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hägglund, R
    SCA Packaging Research.
    Kinetics of polyelectrolyte adsorption on cellulosic fibers2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 4, p. 1096-1103Article in journal (Refereed)
    Abstract [en]

    The present investigation has been focused on studying the adsorption of three different molecular mass fractions of a polydimethyldiallylammonium chloride (DMDAAC) (8750 (LMw), 48 000 (MMw), and 1 200 000 (HMw)) on bleached chemical fibers. Both kinetics of adsorption and equilibrium adsorption measurements have been conducted, and the adsorption has been measured by polyelectrolyte titration. The results show that the LMw polymer can reach all the charges in the fiber wall whereas the MMw and HMw can only reach the charges on the external surfaces of the fibers. It is also shown that the kinetics of adsorption of the LMw polymer is not at all affected by the presence of a saturated layer of HMw polymer on the surface of the fibers. Finally the results from the investigation show that it is possible to have a full coverage of the external surface of the fibers by a high molecular mass polymer and a full coverage of the internal surface of the fibers with a low molecular mass polymer provided that the high molecular mass polymer is adsorbed before addition of the low molecular mass polymer. This is true if the polymers are adsorbed to the same type of groups on the fibers. A simplistic model for describing ployelectrolyte adsorption in turbulent flow also shows good agreement with measured values for the low molecular mass polyelectrolyte whereas the agreement for the high molecular polyelectrolyte is not as good. For the high molecular mass polyelectrolyte a more sophisticated model is needed.

  • 21.
    Zhang, Renyun
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Hummelgård, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Olin, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Simple Synthesis of Clay-Gold Nanocomposites with Tunable Color2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 8, p. 5823-5828Article in journal (Refereed)
    Abstract [en]

    Clay-based nanocomposites have been studied for several decades, mainly focusing on clay-polymer nanocomposites. Here, we report on a simple wet chemical method to synthesize clay-APTES-Au (CAAu) nanocomposites, where 3-aminopropyltriethoxysilane (APTES) acts as the linkage. The silane terminal of APTES formed bonds with the clay surface, while the other -NH(2) terminal bonds to gold nanoparticles. The color of clay changed when these CAAu nanocomposites were formed. By changing the size of the gold nanoparticles, the color of CAAu could be adjusted, simply by changing process parameters. TEM characterization of the synthesized nanocomposites showed an even distribution of gold nanoparticles on the clay surfaces. The nanocomposites were stable in strong acid and high concentration of salt conditions, while strong basic solution like NaOH could slightly influence the status of the gold nanoparticles due to the rupture of the Si-O-Si bonds between APTES and clay. To demonstrate the potential for label free sensing application of CAAu nanocomposites, we made hybrids of clay-APTES-Au-HD-Au (CAAuHAu), where hexamethylene diamine (HD) served as links between CAAu nanocomposites and the gold nanoparticles. The color of the composites changed from red to blue, when the hybrids were formed. Moreover, hemoglobin was loaded on the CAAu nanocomposites, which can potentially be used as a biosensor. These synthesized nanocomposites may combine the catalytic properties of clay and the well-known excellent properties of gold nanoparticles, such as the ability to anchor biological and chemical molecules. Furthermore, the color change of CAAu, when the CAAuHAu hybrids were observed, suggests the applications of these nanocomposites in biochemical and chemical sensing.

1 - 21 of 21
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