Στατιστική Μηχανική Μελέτη του Μερικώς Αναμίξιμου Συστήματος 1- Εξανόλης - Ύδατος, με τη Μέθοδο της Μοριακής Δυναμικής Προσομοίωσης

Postgraduate Thesis uoadl:1319754 576 Read counter

Unit:
Κατεύθυνση Φυσικοχημεία
Library of the School of Science
Deposit date:
2012-11-14
Year:
2012
Author:
Δημητρούλης Χρήστος
Supervisors info:
Ιωάννης Σάμιος Καθηγητής ΕΚΠΑ
Original Title:
Στατιστική Μηχανική Μελέτη του Μερικώς Αναμίξιμου Συστήματος 1- Εξανόλης - Ύδατος, με τη Μέθοδο της Μοριακής Δυναμικής Προσομοίωσης
Languages:
Greek
Summary:
In this study we demonstrate for the first time the results obtained by a series
of Molecular Dynamics simulations of the partially miscible mixture of 1-
hexanol/water organic phase at a temperature of 294.5 K and atmospheric
pressure.
In particular, we have conducted MD simulations of the mixture in the
isothermal-isobaric (NPT) ensemble for several mole fractions of water Xw.
The force fields (ff) employed to simulate the mixtures are the well known
SPC/E and UA-TraPPE for the water and 1-hexanol molecules, respectively.
These ffs have been used in previous simulations and are found to provide
acceptable
agreement between experiment and simulation for the bulk properties
of the pure components of the mixture. Moreover the results obtained from the
present study show satisfactory agreement of the bulk thermodynamic properties
between simulation and experiment. Also, we investigated the specific
problem of the intermolecular structure at each mole fraction, Xw, as well as
we explored and analysed the hydrogen bond (HB) network, that is generally
expected to be formed in such kind of solutions.
To study the intermolecular structure, pair radial distribution functions have
been calculated concerning all the interaction sites of the molecules in the
mixtures.
Also, special attention has been paid to interaction molecular sites which
can contribute to the formation of HBs. The analysis of these functions exhibits
the formation of a HB network between 1-hexanol molecules, water molecules
and each other. Furthermore the arrangement of the molecules in the mixture
which is favoured, forms a type of “open” and “close” four site rings
constructed
by water and 1-hexanol molecules in various proportions.
The average number of HBs which are formed between one alcohol molecule
and the water molecules is about two. On the other hand, one water molecule
forms on average three HBs with other molecules (alcohols or/and water) which
allows the connection of each of the four site rings with the rest of the HB
network.
As Xw decreases, the formation of HBs between the 1-hexanol molecules
as well as between 1-hexanol and water molecule is favoured compared to the
water-water HBs formation. From the mean square displacement (MSD) of the
water molecules we were able to calculate translational diffusion
coefficients,Dw,
in each system. The results obtained show that Dw in the mixture is lower by an
order of magnitude relatively to the one in the pure liquid water. Also, the
calculation
of the linear velocity auto-correlation (AC) functions for the water molecule
in the mixtures confirms and clarifies the former result. Finally,
reorientational
correlation times of the water molecules have been also calculated from the 1st
and 2st order Legendre’s specific unit vectors AC functions. The results exhibit
strong dependence of these times on the composition of the mixtures, which are
generally greater than the corresponding ones observed in pure water system,
suggesting a great rotational motion hindrance of the water by the 1-hexalone
molecules.
Keywords:
Statistical Mechanics, Molecular Dynamics, 1-hexanol, Hydrogen bonds, Diffusion
Index:
Yes
Number of index pages:
1-10
Contains images:
Yes
Number of references:
51
Number of pages:
106
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