title: The temperature dependent structure of liquid 1-propanol as studied by neutron diffraction and EPSR simulations.
abstract: The structure of liquid 1-propanol is investigated as a function of temperature using neutron diffraction 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 cluster 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 (R(mn)) 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, R(g) ∝ n(1/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.
authors.affiliation: Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden. per.sillren@chalmers.se
authors.forename: Per
authors.initials: P
authors.lastname: Sillrén
authors.forename: Jan
authors.initials: J
authors.lastname: Swenson
authors.forename: Johan
authors.initials: J
authors.lastname: Mattsson
authors.forename: Daniel
authors.initials: D
authors.lastname: Bowron
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Matic
mesh_terms: D000433:1-Propanol / Q000737:chemistry*; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D015394:Molecular Structure; D009010:Monte Carlo Method; D033363:Neutron Diffraction; D013696:Temperature
chemical_list: D000433:1-Propanol