| 1. |
- Ahlström, Bodil, 1968, et al.
(författare)
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Prediction of structures and gel transitions in systems of colloids with moderate-range attractions
- 2007
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Ingår i: Journal of Physics. Condensed Matter. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19, s. 036102-036117
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Tidskriftsartikel (refereegranskat)abstract
- Predictions of glass transitions from the idealized mode-coupling theory (MCT) are tested for systems with intermediate-range particle attractions. Liquid structure input to MCT is provided by the Asakura–Oosawa (AO) theory for the depletion interaction, used as an idealized model for structures in colloid–polymer mixtures. The effective one-component formulation of the AO theory is verified to capture the complete pair structure found from the binary version of the theory also for polymer–colloid size ratios somewhat larger than those for which an exact mapping of the two descriptions holds. The Percus–Yevick theory is shown to provide an accurate structural input to MCT, at least in the single-phase fluid region. With this combination of theories, very reasonable predictions for locations of glassy states in the experimental phase diagram are obtained for polymer–colloid size ratios somewhat larger than have been considered before. Simple approximations are also suggested for extracting the remaining pair structure from calculations of the one-component AO theory.
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| 2. |
- Ahlström, Bodil, 1968
(författare)
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Structure, phase behavior, and dynamics of colloidal systems characterized by strong, short- and moderate-ranged attractions: a computational study
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Attractions between colloidal particles are often so strong that non-equilibrium behavior results. However, dissolved non-adsorbing polymer can be added to give a weak attraction between particles so that equilibrium phase transitions appear at moderate polymer concentrations. At higher polymer concentrations and small polymer-colloid size ratios non-equilibrium effects like gelation occur, for which a complete understanding is lacking. Monte Carlo and Monte Carlo-like computer simulations have been used to investigate the role of many-body effects and the structures that colloidal particles adopt under influence of a polymer-induced depletion attraction. The phase diagram proves difficult to determine for these systems by direct application of the Gibbs ensemble Monte Carlo method, especially for small polymer-colloid size ratios that correspond to short-range attractions. However, a sequential equilibration scheme is shown be able to give equilibrated fluid-fluid coexistence data where usual application of the method fails. The dynamics of colloidal particles along this fluid-fluid coexistence curve is studied by a Brownian dynamics algorithm, corrected for the use of a large time step. The dynamics slows down as the particle and polymer concentrations are increased, but the systems appear to reach equilibrium for the cases studied. This is in contrast to what is found by applying mode coupling theory; it predicts glass-like transitions already at modest polymer concentrations for short-range attractive systems, which is an issue that is investigated to some extent. In addition, a number of approximate theories have been developed and tested against the results from the computer simulations.
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| 3. |
- Bergenholtz, Johan, 1964, et al.
(författare)
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Equilibration of fluid-phase coexistence in polydisperse particle systems with short- and moderate-range depletion attractions
- 2011
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Ingår i: Fluid Phase Equilibria. - : Elsevier BV. - 0378-3812. ; 305:1, s. 9-18
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Tidskriftsartikel (refereegranskat)abstract
- Gibbs ensemble Monte Carlo (GEMC) simulations have been done on polydisperse systems of particles interacting via the Asakura-Oosawa depletion potential. On restricting the range of the depletion attraction particles aggregate forming long-lived. unequilibrated structures and it becomes increasingly difficult to sample phase space. It is found that by simply equilibrating systems sequentially starting at longer ranges of attraction, the equilibrium fluid-fluid phase coexistence can be determined down to polymer-colloid size ratios approaching 10%. For such short ranges of the depletion interaction it becomes difficult to obtain reliable estimates of chemical potentials due to occasional particle insertions resulting in very low energies. The results show that full equilibrium is not reached at a polymer-colloid size ratio of 10% in spite of lengthy simulations due to persistent structures in the dense-fluid phase dominated by particles belonging to the larger size fraction. Free-volume theory with a polydisperse colloid component, modeled as a three-component mixture, is used for qualitative comparison with some of the results of the computer simulations.
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| 4. |
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| 5. |
- Cha, S., et al.
(författare)
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Structures of ionic liquid-water mixtures investigated by IR and NMR spectroscopy
- 2014
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 16:20, s. 9591-9601
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Tidskriftsartikel (refereegranskat)abstract
- Imidazolium-based ionic liquids having different anions 1-butyl-3-methylimidazolium ([BMIM] X: X = Cl-, Br-, I-, and BF4-) and their aqueous mixtures were investigated by IR absorption and proton NMR spectroscopy. The IR spectra of these ionic liquids in the CHx stretching region differed substantially, especially for C-H bonds in the imidazolium ring, and the NMR chemical shifts of protons in the imidazolium ring also varied markedly for ILs having different anions. Upon the introduction of water to screen the electrostatic forces and separate the ions, both IR and NMR spectra of [BMIM] X (X = Cl-, Br-, I-) showed significant changes, while those of [BMIM] BF4 did not change appreciably. H-D isotopic exchange rates of C(2)-H in [BMIM] X-D2O mixtures exhibited an order: C(2)-H center dot center dot center dot Cl > C(2)-H center dot center dot center dot Br > C(2)-H center dot center dot center dot I, while the C(2)-H of [BMIM] BF4 was not deuterated at all. These experimental findings, supported by DFT calculations, lead to the microscopic bulk configurations in which the anions and the protons of the cations in the halide ionic liquids have specific, hydrogen-bond type of interaction, while the BF(4)(-)anion does not participate in the specific interaction, but interacts less specifically by positioning itself more above the ring plane of the imidazolium cation. This structural change dictated by the anion type will work as a key element to build the structure-property relationship of ionic liquids.
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| 6. |
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| 7. |
- Nilsson Hallén, Jonathan, 1997, et al.
(författare)
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Ionic Liquids: A Simple Model to Predict Ion Conductivity Based on DFT Derived Physical Parameters
- 2019
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Ingår i: Frontiers in Chemistry. - : Frontiers Media SA. - 2296-2646. ; 7:MAR
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Tidskriftsartikel (refereegranskat)abstract
- A model able to a priori predict ion conductivities of ionic liquids (ILs) is a desired design tool. We here propose a set of simple conductivity models for ILs composed of small ions by only using data easily derived from standard DFT calculations as input; ion volume, ion mass, ion moment of inertia, and the ion-ion interaction strength. Hence these simple models are totally without any need for experimental parametrization. All model are made from fits of 22 ILs based on 12 different cations and 5 different anions, resulting in correlations vs. experiment of R-2 approximate to 0.95 and MAE of 25-36%. Given their (very) simple layout and how fast they can be applied (and re-used), the models allow for ample screening of new IL designs, while not aimed for perfect predictions per se.
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