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• 1.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Aqueous Brønsted–Lowry Chemistry of Ionic Liquid Ions2015In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, no 11, p. 2432-2439Article in journal (Refereed)

Ionic liquids have become commonplace materials found in research laboratories the world over, and are increasingly utilised in studies featuring water as co-solvent. It is reported herein that proton activities, aH+, originating from auto-protolysis of H2O molecules, are significantly altered in mixtures with common ionic liquids comprised of Cl, [HSO4], [CH3SO4], [CH3COO], [BF4], relative to pure water. paH+ values, recorded in partially aqueous media as −log(aH+), are observed over a wide range (∼0–13) as a result of hydrolysis (or acid dissociation) of liquid salt ions to their associated parent molecules (or conjugate bases). Brønsted–Lowry acid–base character of ionic liquid ions observed is rooted in equilibria known to govern the highly developed aqueous chemistry of classical organic and inorganic salts, as their well-known aqueous pKs dictate. Classical salt behaviour observed for both protic and aprotic ions in the presence of water suggests appropriate attention need be given to relevant chemical systems in order to exploit, or avoid, the nature of the medium formed.

• 2.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Chemistry.
Correlated/non-correlated ion dynamics of charge-neutral ion couples: the origin of ionicity in ionic liquids2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 7, p. 4975-4988Article in journal (Refereed)

Proton/Fluoride spin-lattice ($T_1$) nuclear magnetic relaxation dispersion (NMRD) measurements of 1-butyl-3-methyl-$1H$-imidazolium hexa-fluorophosphate, [$C_4mim][PF_6]$, have been carried out using high field spectrometers and fast-field-cycling instrument at proton Larmor frequencies ranging from 10kHz to 40 MHz, at different temperatures. The NMRD profiles are interpreted by means of a simple relaxation model based on the inter- and intra-ionic dipole-dipole relaxation mechanism. Using an atomic molecular-ion dynamic simulation at 323 K the relevant spin dipole-dipole(DD) correlation functions are calculated. The results indicate the NMRD profiles can be rationalized using intra- and inter-ionic spin DD interactions, however, both are mainly modulated by ionic reorientation because of temporary correlations with cations, where modulation by translational diffusion plays a minor role. Reorientational dynamics of charge-neutral ion couples (i.e. $[C_4mim]^{...}[PF_6]$) and $[C_4mim]^{+}$ ions are in the nano-second (ns) time range whereas the reorientation of $[PF_6]{^-}$ is characterized by a reorientational correlation time in the pico-second (ps) regime. Based on the NMRD profiles we conclude the main relaxation mechanism for $[PF_6]{^-}$ is, due to fast internal reorientational motion, a partially averaged F-F intra and a F-H inter-ionic DD coupling as the anion resides in close proximity to its temporary oppositely charged cation partner. The F-$T_1$- NMRD data display a ns dispersions which is interpreted as being due to correlated reorientational modulations resultant from H-containing charge-neutral ion couple $[C_4mim]^{...}[PF_6]$. The analysis of ionicity is based on the free anion fraction, $f$ and it increase with temperature with $f$ $\rightarrow$ 1 at the highest temperatures investigated. The fraction is obtained from the H-F NMRD profiles as correlated-non-correlated dynamics of the ions. The analysis of $T_1$ relaxation rates of C, H, F and P at high fields cannot generally give the fraction of ion but are consistent with the interpretation based on the NMRD profiles with relaxation contributions due to DD-intra and -inter, CSA-intra (and -inter for C), including spin rotation for P. The investigation has led to a description of the mechanics governing ion transport in the title ionic liquid via identification of transient correlated/non-correlated ion dynamics.

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• 3.
Department of Chemical Engineering.
Non-spherical ion dynamics and rotational diffusion for imidazolium based ionic liquids2011In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, no 4, p. 757-60Article in journal (Refereed)
• 4.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Interpretation of Fusion and Vaporisation Entropies for Various Classes of Substances, with a Focus on Salts2014In: Journal of Chemical Thermodynamics, ISSN 0021-9614, E-ISSN 1096-3626, Vol. 70, no March 2014, p. 207-2013Article in journal (Refereed)

Entropies of fusion and vaporisation of a variety of elements and compounds have been derived from literature data. Fusion entropies range from low values for metals and certain cyclic hydrocarbons (e.g. cyclopentane) through modest values for salts to high values for materials undergoing drastic rearrangement or disentanglement such as aluminium chloride and n-alkanes. Entropies of vaporisation for most substances are close to the Trouton’s Law value of ∼100 J deg.-1 mol.-1, with low values for species which associate on boiling (e.g. acetic acid) and higher values signifying simple dissociation (e.g. nitrogen tetroxide) or total decomposition (e.g. some ionic liquids). The nature of inorganic and semi-organic salts in all 3 phases is discussed.

• 5.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
The complex story of a simple Brønsted acid: Unusual speciation of HBr in an ionic liquid medium2011In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, no 41, p. 10801-10803Article in journal (Refereed)

Crystalline solids, co-existing in equilibrium with the 3-methyl-1H-imidazolium bromohydrogenates(i) ionic liquid, have been characterised by X-ray diffraction analysis. The Brønsted acidic, homo-conjugate [H(2)Br(3)](-) anions presented are discussed in terms of their structure and reactivity, in efforts to advance the understanding of Brønsted acidity in ionic liquid media.

• 6.
Department of Physical Chemistry II, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, D-44780 Bochum, Germany.
Department of Physical Chemistry II, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, D-44780 Bochum, Germany. Department of Physical Chemistry II, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, D-44780 Bochum, Germany. Department of Chemical Engineering, Laboratory of Analytical Chemistry, Åbo Akademi University. Department of Physical Chemistry II, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, D-44780 Bochum, Germany.
Static Relative Dielectric Permittivities of Ionic Liquids at 25 °C2011In: Journal of Chemical and Engineering Data, ISSN 0021-9568, E-ISSN 1520-5134, Vol. 56, no 4, p. 1494-1499Article in journal (Refereed)

For understanding solvation by ionic liquids, it is mandatory to characterize their static relative dielectric permittivities ε (“static dielectric constants”). Exploiting the definition of ε in terms of the zero-frequency limit of the frequency-dependent dielectric dispersion curve, the static dielectric constant of an electrically conducting liquid can be extrapolated from dielectric relaxation spectra in the microwave regime. On the basis of this method, we report dielectric constants of 42 ionic liquids at 25 °C.

• 7. Ingman, Petri
Umeå University, Faculty of Science and Technology, Department of Chemistry.
A quantitative ionicity scale for liquid chloride salts2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 37, p. 13053-13057Article in journal (Refereed)

Knowledge of ionicity is requisite for successful identification of those salt qualities required to design and couple the most appropriate fluid for performance of an intended chemical function. We report on utilisation of 35Cl quadrupolar coupling constants (CQ) to quantitatively assess the ionicities of given chloride salts, by exploiting the electronic response of the quadrupolar chlorine atom as a function of its immediate chemical environment. We find that protic salts in particular, like their aprotic analogues, are highly ionised, while at the same time being highly associated, in stark contrast to literature reports claiming in general that they are of sub-ionic origin.

• 8. Mihichuk, L M
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Acidity in Ionic Liquids2011In: Metals and Materials Processing in a Clean Environment: Volume 3: Molten Salts & Ionic Liquids 2011 / [ed] Florian Kongoli, FLOGEN, 2011, p. 307-315Conference paper (Other academic)

A discussion of acidity is developed from the simplest situation - the gas phase. The formation of acids in protic liquids, in solution in molecular liquids and in alreadey ionized liquids is discussed. The distinction between aqueous and other systems, including the question of speciation of actual acidic ions, is emphasized. The measurement of acidity by spectrophotometric and eletrochemical procedures is presented with examples. Tables of selected proton affinities and acidities in a variety of liquids are included.

• 9. Mihichuk, Lynn M
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Brønsted acidity and the medium: fundamentals with a focus on ionic liquids2011In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, no 9, p. 1622-1632Article in journal (Refereed)

Fundamental aspects of Brønsted acidity in ionic liquid systems, in relation to those of simple protic molecules in the gas phase, pure protic molecules in the condensed phase and solutions of protic molecules in molecular systems, are presented. The variety of acidities possible, beyond those observed in aqueous systems, is emphasised and discussed in terms of differences of solvent levelling, ionisation, dissociation, homo-/hetero-conjugate ion speciation and the stabilisation of proton-transfer products from solvent to solvent. It is argued that data regarding aqueous systems do not necessarily explain acid/base behaviour in other liquids satisfactorily. Methods of measuring acidity are reviewed, particularly by spectrophotometry and electrochemistry and recommendations proffered for estimating speciation and acidity of ionic liquids of various complexities.

• 10.
Umeå University, Faculty of Science and Technology, Department of Chemistry. Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, UK.
Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Chemistry. Umeå University, Faculty of Science and Technology, Department of Chemistry.
Bifluoride ([HF2](-)) formation at the fluoridated aluminium hydroxide/water interface2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 22, p. 9045-9050Article in journal (Refereed)

This study uncovers bifluoride-type (difluorohydrogenate(I); [HF2](-)) species formed at mineral/water interfaces. Bifluoride forms at equivalent to Al-F surface sites resulting from the partial fluoridation of gibbsite (gamma-Al(OH3)) and bayerite (alpha-Al(OH3)) particles exposed to aqueous solutions of 50 mM NaF. Fluoride removal from these solutions is proton-promoted and results in a strongly self-buffered suspensions at circumneutral pH, proceeds at a F : H consumption ratio of 2 : 1, and with recorded losses of up to 17 mM fluoride (58 F nm(-2)). These loadings exceed crystallographic site densities by a factor of 3-4, yet the reactions have no resolvable impact on particle size, shape and mineralogy. X-ray photoelectron spectroscopy (XPS) of frozen (-155 degrees C) wet mineral pastes revealed coexisting surface F- and HF0 species. Electron energy loss features pointed to multilayer distribution of these species at the mineral/water interface. XPS also uncovered a distinct form of Na+ involved in binding fluoride-bearing species. XPS and solid state magic angle spinning F-19 nuclear magnetic resonance measurements showed that these fluoride species were highly comparable to a sodium-bifluoride (NaHF2) reference. First layer surface species are represented as =Al-F-H-F-Al= and =Al-F-Na-F-Al=, and may form multi-layered species into the mineral/water interface. These results consequently point to a potentially overlooked inorganic fluorine species in a technologically relevant mineral/water interfacial systems.

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