| 1. |
- Forsberg, Björn, 1971, et al.
(författare)
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Dressed ion theory of size-asymmetric electrolytes: effective ionic charges and the decay length of screened Coulomb potential and pair correlations.
- 2005
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:6
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Tidskriftsartikel (refereegranskat)abstract
- The effects of ionic size asymmetry on long-range electrostatic interactions in electrolyte solutions are investigated within the primitive model. Using the formalism of dressed ion theory we analyze correlation functions from Monte Carlo simulations and the hypernetted chain approximation for size asymmetric 1:1 electrolytes. We obtain decay lengths of the screened Coulomb potential, effective charges of ions, and effective permittivity of the solution. It is found that the variation of these quantities with the degree of size asymmetry depends in a quite intricate manner on the interplay between the electrostatic coupling and excluded volume effects. In most cases the magnitude of the effective charge of the small ion species is larger than that of the large species; the difference increases with increasing size asymmetry. The effective charges of both species are larger (in absolute value) than the bare ionic charge, except for high asymmetry where the effective charge of the large ions can become smaller than the bare charge.
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| 2. |
- French, Roger H., et al.
(författare)
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Long range interactions in nanoscale science
- 2010
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Ingår i: Reviews of Modern Physics. - 0034-6861. ; 82:2, s. 1887-1944
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Forskningsöversikt (refereegranskat)abstract
- Our understanding of the “long range” electrodynamic, electrostatic, and polar interactions that dominate the organization of small objects at separations beyond an interatomic bond length is reviewed. From this basic-forces perspective, a large number of systems are described from which one can learn about these organizing forces and how to modulate them. The many practical systems that harness these nanoscale forces are then surveyed. The survey reveals not only the promise of new devices and materials, but also the possibility of designing them more effectively.
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| 3. |
- Kjellander, Roland, 1948
(författare)
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A multiple decay-length extension of the Debye–Hückel theory: to achieve high accuracy also for concentrated solutions and explain under-screening in dilute symmetric electrolytes
- 2020
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Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22, s. 23952-23985
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Tidskriftsartikel (refereegranskat)abstract
- The Poisson–Boltzmann and Debye–Hückel approximations for the pair distributions and mean electrostatic potential in electrolytes predict that these entities have one single decay mode with a decay length equal to the Debye length 1/κ_D, that is, they have a characteristic contribution that decays with distance r like exp(-κ_D r)/r. However, in reality, electrolytes have several decay modes exp(-κ r)/r, exp(-κ' r)/r etc. with different decay lengths, 1/κ, 1/κ' etc., that in general are different from the Debye length. As an illustration of the significance of multiple decay modes in electrolytes, the present work uses a very simple extension of the Debye–Hückel approximation with two decay lengths, which predicts oscillatory modes when appropriate. This approach gives very accurate results for radial distribution functions and thermodynamic properties of aqueous solutions of monovalent electrolytes for all concentrations investigated, including high ones. It is designed to satisfy necessary statistical mechanical conditions for the distributions. The effective dielectric permittivity of the electrolyte plays an important role in the theory and each mode has its own value of this entity. Electrolytes with high electrostatic coupling, like those with multivalent ions and/or with solvent of low dielectric constant, have decay lengths in dilute solutions that substantially deviate from the Debye length. It is shown that this is caused by nonlinear ion–ion correlation effects and the origin of under-screening, i.e., 1/κ > 1/κ_D, in dilute symmetric electrolytes is analyzed. The under-screening is accompanied by an increase in the effective dielectric permittivity that is also caused by these correlations. The theoretical results for the decay length are successfully compared with recent experimental data for simple electrolytes in various solvents. The paper includes background material on electrolyte theory and screening in order to be accessible for nonexperts in the field.
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| 4. |
- Kjellander, Roland, 1948
(författare)
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Att konkretisera det abstrakta: Förstå och undervisa om entropi och temperatur
- 2013
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Ingår i: Modeller, analogier och metaforer i naturvetenskapsundervisning. - Lund : Studentlitteratur. - 9789144090009
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Termodynamik har en viktig plats inom fysik, kemi och många ingenjörsämnen. Ämnet bereder dock ofta konceptuella och andra svårigheter bland annat på grund av sin abstrakta natur. Ett begrepp som vållar särskild huvudbry är entropi. Orsaken till detta är mångfaldig. Entropi är en storhet som inte kan mätas direkt, dess definition är inte enkel och den har egenskaper som kan vara svåra att förstå varför den har. Dessa egenskaper är emellertid av fundamental betydelse bland annat för naturliga processer. Svårigheterna med entropibegreppet finns både då det gäller att själv att förstå det och att lära ut det till andra. I kapitlet beskrivs ett möjligt sätt att närma sig begreppen entropi och temperatur som författaren funnit vara en framgångsrik väg för studenter att ta till sig de väsentligaste grunderna. Dessutom diskuteras, utgående från författarens erfarenhet, varför flera andra alternativ inte är lika lämpliga ur ett naturvetenskapligt perspektiv eller inte lika tillgängliga för studenterna.
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| 5. |
- Kjellander, Roland, 1948
(författare)
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Decay behavior of screened electrostatic surface forces in ionic liquids: the vital role of non-local electrostatics
- 2016
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Ingår i: Physical Chemistry Chemical Physics - PCCP. - 1463-9076. ; 18, s. 18985-19000
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Tidskriftsartikel (refereegranskat)abstract
- Screened electrostatic surface forces, also called double layer forces, between surfaces in ionic liquids can, depending on the circumstances, decay in an exponentially damped, oscillatory manner or in a plain exponential way (the latter as in dilute electrolyte solutions where ion–ion correlations are very weak). The occurrence of both of these behaviors in dense ionic liquids, where ion–ion correlations are very strong, is analyzed in the current work using exact statistical mechanics formulated in a manner that is physically transparent. A vital ingredient in understanding the decay behaviors is the fact that electrostatics in dense electrolytes have a non-local nature caused by the strong correlations. It is shown that the effects of non-locality can be elucidated by a remarkably simple, general expression for the decay parameter κ that replaces the classical expression for the inverse Debye length κ_DH of the Debye–Hückel (DH) and non-linear Poisson–Boltzmann approximations. This exact expression is valid for both the plain exponential and the oscillatory cases. It shows how strong correlations can give rise to plain exponential decay with a long decay length. Such a decay can arise from anion–cation associations of various kinds, for instance transient ion pairing or association caused by many-body correlations; ion pairing is a possibility but not a necessity for this to occur. Theoretical analysis is done for systems consisting of ions with an arbitrary shape and internal charge density and immersed planar walls with arbitrary internal charge distribution and any short-range ion–surface interaction. The screened electrostatic surface force between two walls is at large separations proportional to the product of effective surface charge densities of each wall. For the oscillatory case, each wall contributes with a phase shift to the oscillations of the interaction.
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| 6. |
- Kjellander, Roland, 1948
(författare)
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Electrostatic screening in classical Coulomb fluids: exponential or power-law decay or both? An investigation into the effect of dispersion interactions
- 2006
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Ingår i: Journal of Physics a-Mathematical and General. ; 39:17, s. 4631-4641
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that the nature of the non-electrostatic part of the pair interaction potential in classical Coulomb fluids can have a profound influence on the screening behaviour. Two cases are compared: (i) when the non-electrostatic part equals an arbitrary finite-ranged interaction and (ii) when a dispersion r(-6) interaction potential is included. A formal analysis is done in exact statistical mechanics, including an investigation of the bridge function. It is found that the Coulombic r(-1) and the dispersion r(-6) potentials are coupled in a very intricate manner as regards the screening behaviour. The classical one-component plasma (OCP) is a particularly clear example due to its simplicity and is investigated in detail. When the dispersion r(-6) potential is turned on, the screened electrostatic potential from a particle goes from a monotonic exponential decay, exp(-wr)/r, to a power-law decay, r(-8), for large r. The pair distribution function acquire, at the same time, an r(-10) decay for large r instead of the exponential one. There still remains exponentially decaying contributions to both functions, but these contributions turn oscillatory when the r(-6) interaction is switched on. When the Coulomb interaction is turned off but the dispersion r(-6) pair potential is kept, the decay of the pair distribution function for large r goes over from the r(-10) to an r(-6) behaviour, which is the normal one for fluids of electroneutral particles with dispersion interactions. Differences and similarities compared to binary electrolytes are pointed out.
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| 7. |
- Kjellander, Roland, 1948
(författare)
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Electrostatics in Electrolytes Expressed in an Exact Formalism Reminiscent of the Poisson–Boltzmann Picture
- 2014
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Ingår i: Electrostatics of Soft and Disordered Matter. - Singapore : Pan Stanford Publishing. - 9789814411851
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Bokkapitel (refereegranskat)abstract
- In the PB approximation for electrolyte systems one assumes that the solvent behaves like a dielectric continuum and that the charge of each ion interacts with the average electrostatic potential from other ions in the system, neglecting the correlations. In reality an ion does not "feel" the mean potential since the ions and the solvent molecules in its neighborhood correlate with it—each ion has a local "ion and solvent cloud" of its own where the ion distribution deviate from the average one and where the locations and orientations of solvent molecules are affected. This cloud affects the interactions felt by the ion. In this treatise it is shown how it is possible to include such effects in an exact manner for the screened electrostatic interactions. Thereby, the exact theory of electrolyte solutions with discrete solvent molecules is reformulated in a manner that has a similar structure as the PB approximation theory. The screened electrostatic interaction between any two particles in the system is then written in terms of the average electrostatic potential due to one of them interacting with an effective charge distribution of the other (rather than with the bare charges as assumed in the PB approximation). This effective charge distribution also has the role as the source of the average electrostatic potential when the latter is expressed in terms of the screened rather than the ordinary (unscreened) Coulomb potential. The resulting exact formalism maintains a large part of the physical transparency of the PB theory. A major conceptual advantage is that the formalism separates out the screened electrostatics among complex consequences of the various interactions.
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| 8. |
- Kjellander, Roland, 1948
(författare)
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En molekylär introduktion till termodynamik
- 2020
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- Begreppen entropi och fri energi har genom tiderna visat sig särskilt svåra att få grepp om och att förstå för så gott som alla studenter. Termodynamik framställs vanligen på ett ganska matematiskt och abstrakt sätt, vilket ger upphov till denna sorts svårighet. Denna bok visar dock att det inte alltid krävs en massa matematik för att få en intuitiv förståelse av termodynamikens väsentligaste principer om de belyses utifrån molekylära sammanhang. Framställningen är i stor utsträckning baserad på bilder och enkla resonemang som leder till de korrekta matematiska sambanden. Boken är upplagd så att den kan användas på förstaårsnivå och uppåt inom universitets- och högskolestudier i naturvetenskapliga ämnen. Den kan läsas som en fristående bok eller utgöra ett komplement till den gängse kurslitteraturen.
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| 9. |
- Kjellander, Roland, 1948
(författare)
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Focus Article: Oscillatory and long-range monotonic exponential decays of electrostatic interactions in ionic liquids and other electrolytes: The significance of dielectric permittivity and renormalized charges
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 148:19
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Tidskriftsartikel (refereegranskat)abstract
- A unified treatment of oscillatory and monotonic exponential decays of interactions in electrolytes is displayed, which highlights the role of dielectric response of the fluid in terms of renormalized (effective) dielectric permittivity and charges. An exact, but physically transparent statistical mechanical formalism is thereby used, which is presented in a systematic, pedagogical manner. Both the oscillatory and monotonic behaviors are given by an equation for the decay length of screened electrostatic interactions that is very similar to the classical expression for the Debye length. The renormalized dielectric permittivities, which have similar roles for electrolytes as the dielectric constant has for pure polar fluids, consist in general of several entities with different physical meanings. They are connected to dielectric response of the fluid on the same length scale as the decay length of the screened interactions. Only in cases where the decay length is very long, these permittivities correspond approximately to a dielectric response in the long-wavelength limit, like the dielectric constant for polar fluids. Experimentally observed long-range exponentially decaying surface forces are analyzed as well as the oscillatory forces observed for short to intermediate surface separations. Both occur in some ionic liquids and in concentrated as well as very dilute electrolyte solutions. The coexisting modes of decay are in general determined by the bulk properties of the fluid and not by the solvation of the surfaces; in the present cases, they are given by the behavior of the screened Coulomb interaction of the bulk fluid. The surface-fluid interactions influence the amplitudes and signs or phases of the different modes of the decay, but not their decay lengths and wavelengths. The similarities between some ionic liquids and very dilute electrolyte solutions as regards both the long-range monotonic and the oscillatory decays are analyzed. Published by AIP Publishing.
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| 10. |
- Kjellander, Roland, 1948
(författare)
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Fundamental aspects of electrostatic interactions and charge renormalization in electrolyte systems
- 2007
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Ingår i: Colloid Journal. ; 69:1, s. 20-28
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Tidskriftsartikel (refereegranskat)abstract
- The consistent inclusion of ion-ion correlations and molecular solvent effects in electrolyte theory can be expressed in a physical formalism, where the particles acquire a renormalized charge density and where they interact electrostatically via a generalized screened Coulomb potential. The latter usually decays for large distances r like a Yukawa function exp(-kappa r)/r, where 1/kappa is the decay length (normally different from the Debye length), but, for smaller r, the screened Coulomb potential is a more complicated function. The resulting electrostatic theory, "Yukawa electrostatics", differs in many important aspects from ordinary (unscreened) Coulomb electrostatics. In the present paper, we give illustrations and explanations of some important differences between Coulomb and Yukawa electrostatics. The effective "Yukawa charge" of a particle differs from the ordinary Coulombic charge. Furthermore, contributions from multipoles of all orders contribute, in general, to the leading asymptotic term in the potential for large r, which decays like exp(-kappa r)/r. Thus, the electrostatic potential from, for example, an electroneutral molecule with an internal charge distribution has generally the same range as the potential from an ion. Some implications of these facts are pointed out. The presentation is based on exact statistical mechanical analysis where all particles are treated on the same fundamental level, but the main focus lies on physical consequences and interpretations of the theory.
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