| 1. |
- Hansen, Elisabeth Lindbo, et al.
(författare)
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Orientational order in a glass of charged platelets with a concentration gradient
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 9:42, s. 9999-10004
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal dispersions of anisometric particles can display dynamical arrest and ordering involving both translational and rotational degrees of freedom. We show that orientational order can develop in glassy colloidal dispersions of charged platelets when a concentration gradient is imposed through solvent evaporation. Our model system of Laponite (LRD) platelets in deionized water has been extensively studied for its ergodic to non-ergodic transitions, and the existence of an underlying isotropic-nematic phase transition has been a subject of debate. We use small-angle X-ray scattering, dynamical light scattering and birefringence to show that the orientational order we observe does not result from an underlying, uniquely determined equilibrium state with orientational order, but from plastic deformation of the colloidal glass.
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| 2. |
- Hemmen, Henrik, et al.
(författare)
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X-ray Studies of Carbon Dioxide Intercalation in Na-Fluorohectorite Clay at Near-Ambient Conditions
- 2012
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 28:3, s. 1678-1682
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedWe show experimentally that gaseous CO2 intercalates into the interlayer space of the synthetic smectite clay Na-fluorohectorite at conditions nottoo far from ambient. The mean interlayer repetition distance of the clay when CO2 is intercalated is found to be 12.5 Å for the conditions −20 °C and 15 bar. The magnitude of the expansion of the interlayer upon intercalation is indistinguishable from that observed in the dehydrated−monohydrated transition for H2O, but the possibility of water intercalation is ruled out by a careful analysis of the experimental conditions and repeating the measurements exposing the clay to nitrogen gas. The dynamics of the process is observed to be dependent on the pressure, with a higher intercalation rate at increased pressure. The rate of CO2 intercalation at the studied conditions is found to be several orders of magnitude slower than the intercalation rate of water or humidity at ambient pressure and temperature.
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| 3. |
- Larsen, Simon R., et al.
(författare)
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Physicochemical characterisation of fluorohectorite : Water dynamics and nanocarrier properties
- 2020
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 306
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Tidskriftsartikel (refereegranskat)abstract
- Clay minerals such as fluorohectorite (FHt) have come into prominence as drug carrier systems due to their layered structure and excellent cation exchange capabilities. Water present in the interlayers of FHt is believed to facilitate the uptake of bio-active molecules in these systems, yet details of this interaction are not well understood. To shed light into this question, using quasi-elastic neutron scattering and the jump diffusion model, we determined the diffusion coefficients and the residence time of water in this synthetic smectite clay. We demonstrate how different interlayer cations (Li+, Na+ and Ni2+) and different hydration levels influenced water mobility in FHt. By means of the elastic window method and analysis of the thermal decomposition of samples with the drug Ciprofloxacin intercalated at pH 2 in LiFHt, we confirmed that the intercalation process removed most of the interlayer water previously present in the clay. Based on the Kissinger procedure, we also showed that thermal decomposition of the intercalated drug was activated at lower temperature. These findings are discussed in relation to the drug's shelf life and might aid in the selection of clay systems for use as nanocarrier.
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| 4. |
- Larsen, Simon R., et al.
(författare)
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Sample cell for studying liquid interfaces with an in situ electric field using X-ray reflectivity and application to clay particles at oil–oil interfaces
- 2018
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 25:Part: 3, s. 915-917
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Tidskriftsartikel (refereegranskat)abstract
- Commissioning results of a liquid sample cell for X-ray reflectivity studies with an in situ applied electrical field are presented. The cell consists of a Plexiglas container with lateral Kapton windows for air-liquid and liquid-liquid interface studies, and was constructed with grooves to accept plate electrodes on the walls parallel to the direction of the beam. Both copper and ITO plate electrodes have been used, the latter being useful for simultaneous optical studies. Commissioning tests were made at the I07 beamline of the Diamond Light Source.
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| 5. |
- Mauroy, Henrik, et al.
(författare)
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Anisotropic clay–polystyrene nanocomposites: Synthesis, characterization and mechanical properties
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 1872-9053 .- 0169-1317. ; 108, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies on clay–polymer nanocomposites have shown prominent improvements in thermal and mechanical propertieswith the addition of quite small amounts of nanometer sized clay particles. The present work presents characterization of anisotropic clay–polystyrene nanocomposites synthesized via a guided self-assembly technique, employing electric fields to align the clay particles into chain-like structures inside the polymer matrix. Four different kinds of surface modified clay were used as particle additives, namely Hectorite, Laponite, Na-Montmorillonite and Li-Fluorohectorite. The microstructure of the nanocomposites was examined with wide angle X-ray scattering (WAXS), X-ray computed microtomography (XMT) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) was further employed to examine the high-temperature resilience of the nanocomposites before determination of the mechanical properties during compression. The results showed that the nanocomposites were of the intercalated type with the clay dispersed as ~15–70 nm thick crystallites which in turn aggregated into micrometer sized particles. Alignment of the clay particles into chains inside the polymer matrix led to differences in mechanical properties compared to nanocomposites having a randomorientation of the clay particles. In particular the aligned polystyrene–fluorohectorite nanocomposite displayed large improvements compared to its non-aligned counterpart. It was also observed that differences in yield strength depended on the compression direction.
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| 6. |
- Mauroy, Henrik, et al.
(författare)
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Oxygen-Controlled Phase Segregation in Poly(N‑isopropylacrylamide)/Laponite Nanocomposite Hydrogels
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29, s. 371-379
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Tidskriftsartikel (refereegranskat)abstract
- The combination of nanoparticles and polymers into nanocomposite gels has been shown to be a promising route to creating soft materials with new or improved properties. In the present work, we have made use of Laponite nanoparticles in combination with a poly(N-isopropylacrylamide) (PNIPAAM)polymer and describe a phenomenon taking place during the polymerization and gelling of this system. The presence of small amounts of oxygen in the process induces two distinctly separated phases, one polymer-rich and one polymer-deficient water−clay phase. Complex interactions among clay, oxygen, and the polymer are found to govern the behavior of these phases. It is also observed that the initial clay concentration can be used to control the volume fraction of the polymer-deficient phase directly. The dynamics of the phase boundary is found to be dependent on water penetration and in general to exhibit non-Fickian behavior. An approach using video recording to monitor hydrogel swelling is also presented, and its advantages are addressed.
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| 7. |
- Michels, Leander, et al.
(författare)
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Intercalation and Retention of Carbon Dioxide in a Smectite Clay promoted by Interlayer Cations
- 2015
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- A good material for CO2 capture should possess some specific properties: (i) a large effective surface area with good adsorption capacity, (ii) selectivity for CO2, (iii) regeneration capacity with minimum energy input, allowing reutilization of the material for CO2 adsorption, and (iv) low cost and high environmental friendliness. Smectite clays are layered nanoporous materials that may be good candidates in this context. Here we report experiments which show that gaseous CO2 intercalates into the interlayer nano-space of smectite clay (synthetic fluorohectorite) at conditions close to ambient. The rate of intercalation, as well as the retention ability of CO2 was found to be strongly dependent on the type of the interlayer cation, which in the present case is Li1, Na1 or Ni21. Interestingly, we observe that the smectite Li-fluorohectorite is able to retain CO2 up to a temperature of 356C at ambient pressure, and that the captured CO2 can be released by heating above this temperature. Our estimates indicate that smectite clays, even with the standard cations analyzed here, can capture an amount of CO2 comparable to other materials studied in this context.
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| 8. |
- Rozynek, Zbigniew, et al.
(författare)
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Organoclay polypropylene nanocomposites under different electric field strengths
- 2014
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Ingår i: Applied Clay Science. - : Elsevier BV. - 1872-9053 .- 0169-1317. ; 96, s. 67-72
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Tidskriftsartikel (refereegranskat)abstract
- Functionalities of clay-polymer nanocomposites (CPN) are related to the degree of clay particle exfoliation and orientation within the polymer matrix. Exploration of new physical methods for such CPN processing is currently an active field of research. In the present work, organoclay polypropylene nanocomposites were prepared by melt intercalation and subsequently exposed to an electric field (E) and studied in-situ by means of synchrotron X-ray scattering. Experiments were performed both at room temperature, and in the melted state (up to 200 degrees C) and during solidification (cooling down to room temperature). Structural changes and time evolution of the alignment of the layered silicates at different E-field strengths, as well as, the final degree of their orientation is discussed. Despite many efforts, i.e. applying different E-field strengths, frequencies, and temperatures; E-field-induced clay particle exfoliation was not observed. The final state of the solidified sample is a semi-crystalline polymer matrix with embedded aligned clay particles having intercalated morphologies. E-field-assisted control of clay layers exfoliation in polymer matrices remains challenging. (C) 2014 Elsevier B.V. All rights reserved.
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