| 1. |
- Bialik, Erik, et al.
(författare)
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Ionization of Cellobiose in Aqueous Alkali and the Mechanism of Cellulose Dissolution
- 2016
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society. - 1948-7185. ; 7:24, s. 5044-5048
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.
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| 2. |
- Abrikossov, Alexei, et al.
(författare)
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Steering patchy particles using multivalent electrolytes
- 2017
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 13:26, s. 4591-4597
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Tidskriftsartikel (refereegranskat)abstract
- Proteins and many recently designed colloids can be regarded as patchy particles where directional interactions strongly influence and govern assembly behavior. Using explicit ion implicit solvent Metropolis Monte Carlo simulations, we investigate spherical model particles, carrying both charge and electric patches, in dilute aqueous 1 : 1, 1 : 3, and 3 : 1 electrolyte solutions. Striking differences in pair interaction free energies and orientational correlations are induced by three different salts which are discussed and rationalized in terms of ion-binding to surface groups, ion-ion correlations, and double layer forces. These findings suggest a general strategy where directional, intermolecular interactions can be invoked and tuned via small amounts of a carefully chosen electrolyte.
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| 3. |
- Andersson, Maria, et al.
(författare)
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Interindividual differences in initial DNA repair capacity when evaluating H2O2-induced DNA damage in extended-term cultures of human lymphocytes using the comet assay
- 2007
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Ingår i: Cell Biology and Toxicology. - : Springer Science and Business Media LLC. - 0742-2091 .- 1573-6822. ; 23:6, s. 401-411
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Tidskriftsartikel (refereegranskat)abstract
- It has been suggested that extended-term cultures of human lymphocytes could be used as a complement to cell lines based on transformed cells when testing the genotoxicity of chemicals. To investigate whether the pattern of induced DNA damage and its subsequent repair differs significantly between cultures based on different blood donors, hydrogen peroxide (H2O2)-induced DNA damage was measured in cultures from four different subjects using the comet assay. The DNA damage was significantly increased in all cultures after 10 min exposure to 0.25 mmol/L H2O2, and there was a significant decrease in the H2O2-induced DNA damage in all cultures after 30 min of DNA repair. The level of damage varied between the different donors, especially after the repair. Using PCR and DNA sequencing, exon 5 of the p53 gene was sequenced in the lymphocytes from the donors with the lowest and highest residual damage. No such mutation was found. Mouse lymphoma L5178Y cells carrying the p53 mutation in exon 5 were included as a reference. These cells were found to be less sensitive toward the H2O2-induced DNA damage, and they were also found to have a rather low DNA repair capacity. The demonstrated variation in H2O2-induced DNA damage and DNA repair capacity between the cultures from the different subjects may be important from a risk assessment perspective, but is obviously not of decisive importance when it comes to the development of a routine assay for genotoxicity.
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| 4. |
- Aspelin, Vidar, et al.
(författare)
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Counterintuitive Electrostatics upon Metal Ion Coordination to a Receptor with Two Homotopic Binding Sites
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 144:7, s. 2921-2932
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Tidskriftsartikel (refereegranskat)abstract
- The consecutive binding of two potassium ions to a bis(18-crown-6) analogue of Tröger’s base (BCETB) in water was studied by isothermal titration calorimetry using four different salts, KCl, KI, KSCN, and K2SO4. A counterintuitive result was observed: the enthalpy change associated with the binding of the second ion is more negative than that of the first (ΔH°bind,2 < ΔH°bind,1). This remarkable finding is supported by continuum electrostatic theory as well as by atomic scale replica exchange molecular dynamics simulations, where the latter robustly reproduces experimental trends for all simulated salts, KCl, KI, and KSCN, using multiple force fields. While an enthalpic K+–K+attraction in water poses a small, but fundamentally important, contribution to the overall interaction, the probability of the collapsed conformation (COL) of BCETB, where both crown ether moieties (CEs) of BCETB are bent in toward the cavity, was found to increase successively upon binding of the first and second potassium ions. The promotion of the COL conformation reveals favorable intrinsic interactions between the potassium coordinated CEs, which further contribute to the observation that ΔH°bind,2 < ΔH°bind,1. While the observed trend is independent of the counterion, the origin of the significantly larger magnitude of the difference ΔH°bind,2 - ΔH°bind,1 observed experimentally for KSCN was studied in light of the weaker hydration of the thiocyanate anion, resulting in an enrichment of thiocyanate ions close to BCETB compared to the other studied counterions.
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| 5. |
- Badersten, Björn, et al.
(författare)
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Politisk klokhet
- 2008
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Ingår i: Förmoderna livshållningar. Dygder, värden och kunskapsvägar från antiken till upplysningen.
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Bokkapitel (refereegranskat)
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| 6. |
- Cautela, Jacopo, et al.
(författare)
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Supracolloidal Atomium
- 2020
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 14:11, s. 15748-15756
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Tidskriftsartikel (refereegranskat)abstract
- Nature suggests that complex materials result from a hierarchical organization of matter at different length scales. At the nano- and micrometer scale, macromolecules and supramolecular aggregates spontaneously assemble into supracolloidal structures whose complexity is given by the coexistence of various colloidal entities and the specific interactions between them. Here, we demonstrate how such control can be implemented by engineering specially customized bile salt derivative-based supramolecular tubules that exhibit a highly specific interaction with polymeric microgel spheres at their extremities thanks to their scroll-like structure. This design allows for hierarchical supracolloidal self-assembly of microgels and supramolecular scrolls into a regular framework of “nodes” and “linkers”. The supramolecular assembly into scrolls can be triggered by pH and temperature, thereby providing the whole supracolloidal system with interesting stimuli-responsive properties. A colloidal smart assembly is embodied with features of center-linker frameworks as those found in molecular metal–organic frameworks and in structures engineered at human scale, masterfully represented by the Atomium in Bruxelles.
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| 7. |
- Idström, Alexander, et al.
(författare)
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Dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide
- 2016
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Ingår i: The 7th Workshop on cellulose, regenerated cellulose and cellulose derivatives. ; , s. 15-18
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The dissolution of cellulose in tetrabutylammonium acetate (TBAAc)/dimethyl sulfoxide (DMSO) was studied combining experimental and simulation techniques. It was found that the dissolution limit at 40 °C corresponded to a molar ratio close to one acetate per cellulose anhydroglucose units. MD simulations suggested that the acetate ions bind to cellulose by dual hydrogen bonds. This effectively turns cellulose into a polyelectrolyte, attracting the bulky tetrabutylammonium (TBA+) counter ions, which prevent close contact between chains in the dissolved state. This hypothesis was tested by 1H- and 13C-NMR spectroscopy, which confirmed that acetate forms hydrogen bonds to cellulose, and by diffusion NMR spectroscopy, which demonstrated a strong dynamic correlation between bound acetate and tetrabutylammonium in near-quantitative agreement with simulation. The present results suggest that offering hydrogen bonding to the acetate ions is the main driving force for dissolving cellulose and that the TBA+ counter ions form a diffuse layer around the acetate-decorated cellulose chains.
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| 8. |
- Idström, Alexander, et al.
(författare)
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On the dissolution of cellulose in tetrabutylammonium acetate/dimethyl sulfoxide : a frustrated solvent
- 2017
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 24:9, s. 3645-3657
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Tidskriftsartikel (refereegranskat)abstract
- We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed.
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| 9. |
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| 10. |
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| 11. |
- Makasewicz, Katarzyna, et al.
(författare)
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Cooperativity of alpha-Synuclein Binding to Lipid Membranes
- 2021
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Ingår i: ACS Chemical Neuroscience. - : American Chemical Society (ACS). - 1948-7193. ; 12:12, s. 2099-2109
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Tidskriftsartikel (refereegranskat)abstract
- Cooperative binding is a key feature of metabolic pathways, signaling, and transport processes. It provides tight regulation over a narrow concentration interval of a ligand, thus enabling switching to be triggered by small concentration variations. The data presented in this work reveal strong positive cooperativity of alpha-synuclein binding to phospholipid membranes. Fluorescence cross-correlation spectroscopy, confocal microscopy, and cryo-TEM results show that in excess of vesicles alpha-synuclein does not distribute randomly but binds only to a fraction of all available vesicles. Furthermore, alpha-synuclein binding to a supported lipid bilayer observed with total internal reflection fluorescence microscopy displays a much steeper dependence of bound protein on total protein concentration than expected for independent binding. The same phenomenon was observed in the case of alpha-synuclein binding to unilamellar vesicles of sizes in the nm and mu m range as well as to flat supported lipid bilayers, ruling out that nonuniform binding of the protein is governed by differences in membrane curvature. Positive cooperativity of alpha-synuclein binding to lipid membranes means that the affinity of the protein to a membrane is higher where there is already protein bound compared to a bare membrane. The phenomenon described in this work may have implications for alpha-synuclein function in synaptic transmission and other membrane remodeling events.
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| 12. |
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| 13. |
- Mihut, Adriana M., et al.
(författare)
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Assembling oppositely charged lock and key responsive colloids: A mesoscale analog of adaptive chemistry
- 2017
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 3:9, s. 1700321-1700321
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Tidskriftsartikel (refereegranskat)abstract
- We have seen a considerable effort in colloid sciences to copy Nature’s successful strategies to fabricate complex functional structures through self-assembly. This includes attempts to design colloidal building blocks and their intermolecular interactions, such as creating the colloidal analogs of directional molecular interactions, molecular recognition, host-guest systems, and specific binding. We show that we can use oppositely charged thermoresponsive particles with complementary shapes, such as spherical and bowl-shaped particles, to implement an externally controllable lock-and-key self-assembly mechanism. The use of tunable electrostatic interactions combined with the temperature-dependent size and shape and van der Waals interactions of these building blocks provides an exquisite control over the selectivity and specificity of the interactions and self-assembly process. The dynamic nature of the mechanism allows for reversibly cycling through various structures that range from weakly structured dense liquids to well-defined molecule-shaped clusters with different configurations through variations in temperature and ionic strength. We link this complex and dynamic self-assembly behavior to the relevant molecular interactions, such as screened Coulomb and van der Waals forces and the geometrical complementarity of the two building blocks, and discuss our findings in the context of the concepts of adaptive chemistry recently introduced to molecular systems.
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| 14. |
- Månberger, André, et al.
(författare)
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Global metal flows in the renewable energy transition : Exploring the effects of substitutes, technological mix and development
- 2018
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Ingår i: Energy Policy. - : Elsevier BV. - 0301-4215. ; 119, s. 226-241
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Tidskriftsartikel (refereegranskat)abstract
- This study analysed demand for 12 metals in global climate mitigation scenarios up to 2060 and quantified the impacts on demand of different assumptions on improvements and technological mix. Annual and cumulative demands were compared with reserves and current mining rates. The study results showed that reserves are sufficient to support the total level of solar power, wind power and electric motors. Insufficient reserves may very well constrain certain sub-technologies, but substitutes that take the role of ‘back-stop’ technologies can be used instead. The exception is batteries, since lithium battery chemistries and reserves were incompatible with the scenarios analysed. Batteries of moderate size, lithium-free chemistry or reserve expansion would make the transition feasible. Choice of sub-technology (e.g. type of solar PV) had a decisive impact on demand for certain metals. Perceptions that many metals are critical and scarce for renewable energy transitions appear exaggerated if a dynamic view on technological development is adopted. Policy-relevant conclusions can be drawn from this, regarding e.g. the benefits of technological diversity, increasing metal intensity, recycling and integrating infrastructure and energy policies (e.g. fast chargers).
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| 15. |
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| 16. |
- Stenberg, Samuel, et al.
(författare)
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Grand canonical simulations of ions between charged conducting surfaces using exact 3D Ewald summations
- 2020
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 22:24, s. 13659-13665
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Tidskriftsartikel (refereegranskat)abstract
- We present a useful methodology to simulate ionic fluids confined by two charged and perfectly conducting surfaces. Electrostatic interactions are treated using a modified 3D Ewald sum, which accounts for all image charges across the conductors, as well as the 2D periodicity, parallel to the surfaces. The energy expression is exact, and the method is trivial to implement in existing Ewald codes. We furthermore invoke a grand canonical scheme that utilizes a bias potential, that regulates the surface charge density. The applied bias potential also enables us to calculate individual chemical potentials of the ions. Finally, we argue that our approach leads to a pedagogically appealing description of the Donnan potential, and what it measures in these systems.
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| 17. |
- Stenqvist, Björn, et al.
(författare)
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Cellulose-Water Interactions: Effect of electronic polarizability
- 2015
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631. ; 30:1, s. 26-31
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Tidskriftsartikel (refereegranskat)abstract
- Understanding cellulose-water interactions is important for advancing current technology, not the least in developing effective dissolution methods for wooden fibers. Here we study the effect of electronic polarization on cellulose-water interactions by all-atom computer simulations. We show that induced dipoles on both interfacial water and cellulose hydroxyl groups are significant and may influence cellulose/co-solute interactions. The non-polarizable SPC/E water model yields remarkably similar solvent radial distribution functions as the polarizable POL3 model while orientational correlations differ slightly. For the present study we have developed a polarizable cellulose force field, based on the popular GLYCAM parameters, as well as tested the Wolf technique for handling long range dipolar interactions in polarizable, all-atom Monte Carlo simulations.
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| 18. |
- Stenqvist, Björn, et al.
(författare)
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Direct summation of dipole-dipole interactions using the Wolf formalism
- 2015
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:1
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Tidskriftsartikel (refereegranskat)abstract
- We present an expanded Wolf formalism for direct summation of long-range dipole-dipole interactions and rule-of-thumbs how to choose optimal spherical cutoff (R-c) and damping parameter (alpha). This is done by comparing liquid radial distribution functions, dipole-dipole orientation correlations, particle energies, and dielectric constants, with Ewald sums and the Reaction field method. The resulting rule states that alpha sigma < 1 and alpha R-c > 3 for reduced densities around rho* = 1 where sigma is the particle size. Being a pair potential, the presented approach scales linearly with system size and is applicable to simulations involving point dipoles such as the Stockmayer fluid and polarizable water models. (C) 2015 AIP Publishing LLC.
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| 19. |
- Stenqvist, Björn
(författare)
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Electric interactions: A study of cellulose
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work is primary about development and application of electrostatic theory within the atomistic domain. The resulting procedures were implemented to eventually describe systems involving the cellulose molecule. A concluding remark about electrostatic interactions is the importance of moment cancellation. By inducing image moments which cancels the totality of the collective system moments, and summing their interactions, long-ranged effects seem to be accurately accounted for in isotropic settings. The performed studies denouement regarding the cellulose molecule is the necessity to account for slight electric structure modifications generated by changing its immediate environment. A concrete conclusion brought forward from this observation is the seemingly important effect of ionizing the polymer in order to achieve solubility.
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| 20. |
- Stenqvist, Björn, et al.
(författare)
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Faunus - a flexible framework for Monte Carlo simulation
- 2013
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Ingår i: Molecular Simulation. - : Informa UK Limited. - 0892-7022 .- 1029-0435. ; 39:14-15, s. 1205-1211
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Tidskriftsartikel (refereegranskat)abstract
- Faunus is a set of building blocks or statistical mechanical Lego' for constructing molecular simulation programs to study complex solutions, including proteins, polymers, salts, phospholipid membranes, surfaces and/or rigid macro-molecules. Current focus is on Metropolis Monte Carlo (MC) algorithms with support for anisotropic particles (multipolar, polarisable and sphero-cylindrical) and a flexible Hamiltonian. The design is inherently modular and it is trivial to extend functionality to cover new interaction potentials, geometries or moves. In this study, we present basic features, C++ design principles and review- selected applications. The latter includes splined pair potentials, two-dimensional parallel tempering of protein mixtures and MC swap moves for modelling ion-specific effects without ions.
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| 21. |
- Stenqvist, Björn, et al.
(författare)
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Generalized Moment Correction for Long-Ranged Electrostatics
- 2020
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 16:6, s. 3737-3745
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Tidskriftsartikel (refereegranskat)abstract
- Describing long-ranged electrostatics using short-ranged pair potentials is appealing because the computational complexity scales linearly with the number of particles. The foundation of the approach presented here is to mimic the long-ranged medium response by cancelling electric multipoles within a small cutoff sphere. We propose a rigorous and formally exact new method that cancels up to infinitely many multipole moments and is free of operational damping parameters often required in existing theories. Using molecular dynamics simulations of water with and without added salt, we discuss radial distribution functions, Kirkwood-Buff integrals, dielectrics, diffusion coefficients, and angular correlations in relation to existing electrostatic models. We find that the proposed method is an efficient and accurate alternative for handling long-ranged electrostatics as compared to Ewald summation schemes. The methodology and proposed parameterization are applicable also for dipole-dipole interactions.
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| 22. |
- Stenqvist, Björn, et al.
(författare)
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Membrane permeability based on mesh analysis
- 2023
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 633, s. 526-535
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Tidskriftsartikel (refereegranskat)abstract
- The main function of a membrane is to control the exchange of matter between the surrounding regions. As such, accurate modeling of membranes is important to properly describe their properties. In many cases in both biological systems and technical applications, the membranes are composite structures where transport properties may vary between the different sub-regions of the membrane. In this work we develop a method based on Mesh analysis that is asymptotically exact and can describe diffusion in composite membrane structures. We do this by first reformulating a generalized Fick's law to include the effects from activity coefficient, diffusion coefficient, and solubility using a single condensed param-eter. We then use the derived theory and Mesh analysis to, in essence, retrieve a finite element method approach. The calculated examples are based on a membrane structure that reassembles that of the brick and mortar structure of stratum corneum, the upper layer of our skin. Resulting concentration profiles from this procedure are then compared to experimental results for the distribution of different probes within intact stratum corneum, showing good agreement. Based on the derived approach we further investigate the impact from a gradient in the fluidity of the stratum corneum mortar lipids across the membrane, and find that it is substantial. We also show that anisotropic organisation of the lipid mortar can have large impact on the effective permeability compared to isotropic mortar lipids. Finally, we examine the effects of corneocyte swelling, and their lateral arrangement in the membrane on the overall membrane permeability.
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| 23. |
- Stenqvist, Björn, et al.
(författare)
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Modeling the assembly of oppositely charged lock- and key-colloids
- 2019
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 15:26, s. 5234-5242
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Tidskriftsartikel (refereegranskat)abstract
- The interaction of oppositely charged lock- and key-colloids is investigated using computer simulations. We show that indented spheres, i.e., lock-particles, can be specifically assembled with spherical key-particles using solely electrostatic interactions in addition to a hard overlap potential. An analytic description of the entropic and energetic contributions is derived and supported by simulations and explicit energy calculations, respectively. The analytic expression of the electrostatic contribution is further employed to build up a schematic model allowing for efficient large-scale Monte Carlo simulations. The influence of the charge/ionic strength, the degree of indentation, and the size/number ratio is discussed by analyzing the specific and unspecific associations from the simulations. Herein, both particle design and mixing conditions lead to the formation of stable specific clusters analogous to colloidal molecules whose valence is defined by the number of lock-particles associated with a key-particle. In addition, the approach is extended to the encapsulation of an excess of small key-particles in largely indented lock-particles. These two examples exemplify that highly specific pairwise interactions can be implemented by using solely oppositely charged particles with complementary geometries, which opens the road for a rational design of complex hierarchical self-assemblies of complementary building blocks.
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| 24. |
- Stenqvist, Björn, et al.
(författare)
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Modeling the assembly of oppositely charged multi-indented lock- and key-colloids
- 2022
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 18:26, s. 4983-4990
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between oppositely charged multi-indented lock- and spherical key-particles are investigated by means of Monte Carlo simulations at low volume fractions. The specificity of the interactions is initially investigated in an excess of either lock- or key-particles, and we find ordered clusters with highly directional bonds. This suggests electrostatics alone to be capable of inducing the assembly of specifically bound clusters. Considering different numbers of indentations and number ratios corresponding to perfect lattices (cubic/hexagonal/diamond), we however only find gel-like structures with no tendency to form dense ordered aggregates or lattices. We conjecture that the high entropic cost that comes with specific binding of several keys to a single lock impedes the spontaneous formation of defined lattices at low volume fractions and “lock” the assembly into disordered gel-like structures.
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| 25. |
- Stenqvist, Björn, et al.
(författare)
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On short-ranged pair-potentials for long-range electrostatics
- 2019
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 21:44, s. 24787-24792
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Tidskriftsartikel (refereegranskat)abstract
- In computer simulations, long-range electrostatic interactions are surprisingly well approximated by truncated, short-ranged pair potentials. Examples are reaction field methods; the Wolf method; and a number of schemes based on cancellation of electric multipole moments inside a cut-off region. These methods are based on the assumption that the polarization of the neglected surroundings can be inferred from a local charge distribution. Multipole moments themselves are only approximations to the true charge distribution, approximations which many times are needed to simplify calculations in complex systems. In this work we investigate a new, generalized pair-potential based on the idea of moment cancellation that covers interactions between electrostatic moments of any type. We find that moment cancellation in itself is insufficient to generate accurate results and a more restricted formalism is needed, in our case to cancel the virtual charges of the imposed moments. Thus, it is unfeasible to cancel higher-order moments with explicit higher-order moments such as dipoles and instead image charges are needed. The proposed pair-potential is general and straight forwardly implementable for any electrostatic moment-monopole, dipole, quadrupole, etc.-with a computational complexity scaling with the number of particles in the system.
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| 26. |
- Stenqvist, Björn, et al.
(författare)
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Tortuosity in the Brick and Mortar Model Based on Chemical Conduction
- 2020
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509. ; 223
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Tidskriftsartikel (refereegranskat)abstract
- Diffusion is a reoccurring phenomena in many fields and is affected by the geometry in which it takes place. Here we investigate the effects of geometry on diffusion in a Brick and Mortar model system. The tortuous effects are evaluated based on generalized Fick's law, i.e. diffusion driven by differences in chemical potential. The presented formalism gives a general (semi-) exact analytic expression for the tortuosity using impermeable bricks, which is successfully validated against standard techniques and finite element method results. The approach allows for anisotropic properties of the mortar, which we show can be significant and is not captured with known analytic techniques. Based on the introduced concept of chemical conductivity we also find generalized Fick's law consistent with Ohm's and Fourier's law in terms of their constituent parts, which further makes the main results for Brick and Mortar structures directly applicable to diffusion of either charge, heat, or mass.
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| 27. |
- Wernersson, Erik, et al.
(författare)
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The mechanism of cellulose solubilization by urea studied by molecular simulation
- 2015
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 22:2, s. 991-1001
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Tidskriftsartikel (refereegranskat)abstract
- We used molecular dynamics simulation to model the effect of urea and thiourea on the solvent quality of aqueous solutions with respect to cellulose. A model system consisting of a periodically replicated cellulose molecule of effectively infinite degree of polymerization immersed in aqueous (thio-)urea solution was considered. Kirkwood-Buff theory, which relates the pair distribution functions to the concentration derivatives of the chemical potential, allowed the solubilization effect to be quantified in terms of the preferential binding of urea over water to the cellulose molecule. We found that urea is preferentially adsorbed on the hydrophobic faces of the anhydroglucose rings but has the same affinity as water to the hydroxyl groups. Thus, the simulations suggest that urea acts primarily by mitigating the effect of the hydrophobic portions of the cellulose molecule.
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