| 1. |
- 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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| 2. |
- 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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