| 1. |
- Sillrén, Per, 1982, et al.
(författare)
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A statistical model of hydrogen bond networks in liquid alcohols
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 136:9, s. 094514-094521
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Tidskriftsartikel (refereegranskat)abstract
- We here present a statistical model of hydrogen bond induced network structures in liquid alcohols. The model generalises the Andersson-Schulz-Flory chain model to allow also for branched structures. Two bonding probabilities are assigned to each hydroxyl group oxygen, where the first is the probability of a lone pair accepting an H-bond and the second is the probability that given this bond also the second lone pair is bonded. The average hydroxyl group cluster size, cluster size distribution, and the number of branches and leaves in the tree-like network clusters are directly determined from these probabilities. The applicability of the model is tested by comparison to cluster size distributions and bonding probabilities obtained from Monte Carlo simulations of the monoalcohols methanol, propanol, butanol, and propylene glycol monomethyl ether, the di-alcohol propylene glycol, and the tri-alcohol glycerol. We find that the tree model can reproduce the cluster size distributions and the bonding probabilities for both mono- and poly-alcohols, showing the branched nature of the OH-clusters in these liquids. Thus, this statistical model is a useful tool to better understand the structure of network forming hydrogen bonded liquids. The model can be applied to experimental data, allowing the topology of the clusters to be determined from such studies.
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| 2. |
- Sillrén, Per, 1982
(författare)
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Hydrogen Bonding in Liquid Alcohols
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogen bonded (H-bonded) materials, such as water, alcohols, sugars, and even DNA, are extremely important for biology, as well as chemical industry. Alcohols are used as solvents in paints, in perfumes, as cleaners, anti-freezers, or as an alternative to petrol in combustion engines. In medicine, the polymeric alcohol polyethylene glycol, PEG, is used in a process called pegylation, where PEG chains are attached to drugs or therapeutic proteins. Pegylation can prolong the medicines half life in the body, as well as aid in making the drug water soluble.Crucial in most of the applications are the effects the H-bonds have on the physical properties of the liquid and its functionality. H-bonds are intermolecular bonds, with a bond strength corresponding to ∼ 10 times the kinetic energy of the molecule at room temperature. In alcohols and water, this leads to a transient H-bond network, where molecules leaves and joins the networks at picosecond timescales. H-bonding is responsible for intriguing properties, both structural and dynamic. The most well known “anomaly”, is probably the density maximum water exhibits at 4◦ C, but also alcohols have unusual properties, caused by H- bonding, such as the so called Debye process seen in dielectric spectra of mono alcohols.To better understand the effect H-bonds have in different materials, it is im- portant to know what the H-bonded structures look like. This thesis is concerned with the H-bonding structure in some of the simplest H-bonding material: small molecule alcohols. To investigate the structure of the H-bonded clusters we use a combinations of experimental, computational, and theoretical methods. The clusters we have found have a tree-like topology, and a broad distribution of cluster sizes.
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| 3. |
- Sillrén, Per, 1982, et al.
(författare)
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Liquid 1-propanol studied by neutron scattering, near-infrared, and dielectric spectroscopy
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 140:12
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Tidskriftsartikel (refereegranskat)abstract
- Liquid monohydroxy alcohols exhibit unusual dynamics related to their hydrogen bonding induced structures. The connection between structure and dynamics is studied for liquid 1-propanol using quasi-elastic neutron scattering, combining time-of-flight and neutron spin-echo techniques, with a focus on the dynamics at length scales corresponding to the main peak and the pre-peak of the structure factor. At the main peak, the structural relaxation times are probed. These correspond well to mechanical relaxation times calculated from literature data. At the pre-peak, corresponding to length scales related to H-bonded structures, the relaxation times are almost an order of magnitude longer. According to previous work [C. Gainaru, R. Meier, S. Schildmann, C. Lederle, W. Hiller, E. Rössler, and R. Böhmer, Phys. Rev. Lett.105, 258303 (2010)] this time scale difference is connected to the average size of H-bonded clusters. The relation between the relaxation times from neutron scattering and those determined from dielectric spectroscopy is discussed on the basis of broad-band permittivity data of 1-propanol. Moreover, in 1-propanol the dielectric relaxation strength as well as the near-infrared absorbance reveal anomalous behavior below ambient temperature. A corresponding feature could not be found in the polyalcohols propylene glycol and glycerol.
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| 4. |
- Sillrén, Per, 1982, et al.
(författare)
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On the critical non-additivity driving segregation of asymmetric binary hard sphere fluids
- 2010
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Ingår i: Molecular Physics. - : Informa UK Limited. - 1362-3028 .- 0026-8976. ; 108:1, s. 97-104
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Tidskriftsartikel (refereegranskat)abstract
- A previously proposed version of thermodynamic perturbation theory, appropriate for singular pair interactions between particles, is applied to binary mixtures of hard spheres with non-additive diameters. The critical non-additivity Delta_C required to drive fluid–fluid phase separation is determined as a function of the ratio xi 0, irrespective of the total packing-fraction eta of the mixture. These results are the basis of an estimate of the range of size ratios for which a binary mixture of additive hard spheres exhibit a fluid–fluid miscibility gap. This range is conjectured to be 0.01
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| 5. |
- Sillrén, Per, 1982, et al.
(författare)
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Perturbation theory for systems with strong short-ranged interactions
- 2007
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Ingår i: Molecular Physics. - 1362-3028 .- 0026-8976. ; 105:13-14, s. 1803-1811
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Tidskriftsartikel (refereegranskat)abstract
- We propose a variant of thermodynamic perturbation theory based on the Mayer f-function which is applicable to strongly repulsive, and even singular interactions. The expansion of the free energy is successfully tested against known 'exact results' for hard-sphere fluids, and then applied to binary mixtures of particles with non-additive hard cores or shouldered potentials. The resulting phase diagrams agree well with existing simulation data and theoretical predictions.
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| 6. |
- Sillrén, Per, 1982, et al.
(författare)
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The temperature dependent structure of liquid 1-propanol as studied by neutron diffraction and EPSR simulations
- 2013
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 138:21, s. 214501-
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Tidskriftsartikel (refereegranskat)abstract
- The structure of liquid 1-propanol is investigated as a function of temperature using neutron diffrac- tion together with Empirical Potential Structure Refinement modelling. The combined diffraction and computer modelling analysis demonstrates that propanol molecules form hydrogen bonded clusters with a relatively wide size distribution, which broadens at lower temperatures. We find that the clus- ter size distribution is well described by a recently proposed statistical model for branched H-bonded networks [P. Sillrén, J. Bielecki, J. Mattsson, L. Börjesson, and A. Matic, J. Chem. Phys. 136, 094514 (2012)]. The average cluster size increases from ∼3 to 7 molecules, whilst the standard deviation of the size distribution increases from 3.3 to 8.5 as the temperature is decreased from 293 to 155 K. The clusters are slightly branched, with a higher degree of branching towards lower temperatures. An analysis of the cluster gyration tensor (Rmn) reveals an average elongated ellipsoidal shape with axes having proportions 1:1.4:1.9. We find that the average radius of gyration has a cluster size dependence consistent with that of fractal clusters, Rg ∝ n1/D , with a fractal dimension D ≈ 2.20, which is close to D = 2.00 expected for an ideal random walk or D = 2.11 expected for reaction limited aggregation. The characteristic angles between the H-bonded OH-groups that constitute the clusters show only a weak temperature dependence with O–H· · ·O angles becoming more narrowly distributed around 180◦ at lower temperatures.
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| 7. |
- Sillrén, Per, 1982
(författare)
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Trees, Queues and Alcohols
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hydrogen bonded (H-bonded) materials, such as water, alcohols, sugars, and even DNA, are extremely important for biology, as well as chemical industry. Alcohols are used as solvents in paints, in perfumes, as cleaners, anti-freezers, or as an alternative to petrol in combustion engines. Crucial in most of the applications are the effects the hydrogen bonds have on the physical properties of the liquid and its functionality.This thesis is concerned with the H-bonding structure and dynamics in some of the simplest H-bonding material: small molecule alcohols. To investigate the structure and dynamics of the H-bonded clusters we use a combination of exper- imental, computational, and theoretical methods. More specifically, a statistical model of the hydrogen bonded clusters is developed that describes the distri- bution of cluster sizes and their properties. The clusters that we find, have a tree-like topology, and a broad distribution of cluster sizes. The model properties are in good agreement with results from Monte Carlo simulations as well as EPSR simulations based on neutron diffraction data. The model is also shown to be compatible with spectroscopic IR- and Raman data.The dynamics of the clusters are captured in a model inspired by queuing theory, with monomers leaving and joining the clusters. The dipole correlation spectrum of the dynamic model explains the Debye peak seen in dielectric spec- tra, and also the different time scales measured by NMR and neutron scattering techniques.
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