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.

Supramolecular x-ray signature of susceptibility amplification in hydrogen-bonded liquids

“…In contrast, the first sharp diffraction peak at q pre ≈ 0.55Å −1 , referred to as a prepeak, is due to oxygen-oxygen (O-O) correlations and gives a handle on supramolecular arrangements in MAs. This assignment of the prepeak as well as of the main peak is well established by combining x-ray data for a large number of MAs with various numerical simulation techniques [26][27][28]. Figure 2(b) reveals that with increasing the 2H1D mole fraction the position of the prepeak shifts to smaller momentum transfers whereas the main peak position q main shifts to larger ones.…”

Size distribution of associated clusters in liquid alcohols: Interpretation of simulation results in the frame of SAFT approach

“…The temperature trends of both characteristics are in agreement with the neutron diffraction data (respectively, Empirical Potential Structure Refinement based on neutron diffraction). 13 The mean values at T = 300 K for propanol and butanol are approximately 25% higher compared with the values of Ref. 33.…”

“…Infrared spectroscopy thus represents the most popular experimental methods to study the microscopic structure of the hydrogen bonded systems. [2][3][4][5][6][7][8] The neutron-or x-ray diffraction techniques [9][10][11][12][13] and the dielectric relaxation 14,15 can provide further information about the structure and dynamics of the hydrogen bonded systems. Indirect information about the hydrogen bonding can be deduced also from macroscopic properties (e.g., from the viscosity measurements or PvT behaviour and phase equilibrium data).…”

Does High Pressure Induce Structural Reorganization in Linear Alcohols? A Computational Answer

“…Herein we have presented an exhaustive overview of the effect of pressure on the structure of n‐alcohols from propanol to octanol by using classical molecular dynamics simulations. Only a few works can be found on simple linear monohydroxy alcohols longer than 1‐propanol, but the simulations at room pressure return results that are in agreement with the most recent findings for all alcohols, which presents a scenario in which a complex supramolecular organization is composed of a variety of hydrogen‐bonded clusters of various shapes and sizes. As the pressure was increased, the peculiar LqP of the SAXS pattern of these compounds gradually shifted to higher q values (i.e.…”