Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт
Методом квазiпружного розсiяння повiльних нейтронiв проведено дослiдження динамiки молекул розчинiв вода–пропиловий спирт рiзної концентрацiї при температурi 281 К. Експериментально виявлено особливостi концентрацiйної залежностi ефективного коефiцiєнта самодифузiї та його одночастинкового внеску, а...
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| Zitieren: | Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт / Л.А. Булавін, Н.О. Атамась, О.А. Василькевич, Г.М. Вербінська, В.І. Слісенко, О.В. Ковальов // Український фізичний журнал. — 2010. — Т. 55, № 6. — С. 694-698. — Бібліогр.: 7 назв. — укр. |
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nasplib_isofts_kiev_ua-123456789-562182025-02-09T20:45:37Z Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт Concentration Specific Features of the Dynamics of Molecules in Solutions Water−Propyl Alcohol Концентрационные особенности динамики молекул в растворах вода—пропиловый спирт Булавін, Л.А. Атамась, Н.О. Василькевич, О.А. Вербінська, Г.М. Слісенко, В.І. Ковальов, О.В. М'яка речовина Методом квазiпружного розсiяння повiльних нейтронiв проведено дослiдження динамiки молекул розчинiв вода–пропиловий спирт рiзної концентрацiї при температурi 281 К. Експериментально виявлено особливостi концентрацiйної залежностi ефективного коефiцiєнта самодифузiї та його одночастинкового внеску, а саме: наявнiсть двох мiнiмумiв в областях концентрацiй (0,04–0,05) м.д. i (0,18–0,22) м.д. спирту та монотонне зростання коефiцiєнта дифузiї при концентрацiях, бiльших за 0,4 м.д. спирту. Результати нейтронного експерименту зiставлено з розрахунками структури указаних розчинiв, проведених методом Монте-Карло. Показано, що мiнiмуми у концентрацiйнiй залежностi коефiцiєнта самодифузiї вiдповiдають певним локальним структурам дослiдженого розчину. By the method of quasielastic scattering of slow neutrons, we study the dynamics of molecules in water–propyl alcohol solutions of various concentrations at a temperature of 281 K. In experiments, we registered specific features of the concentration dependence of the efficient self-diffusion coefficient and its one-particle contribution, namely: the presence of two minima in the regions of (0.04–0.05) mass fractions (m.f.) and (0.18–0.22) m.f. of alcohol and a monotonous increase of the diffusion coefficient at concentrations greater than 0.4 m.f. of alcohol. The results of neutronscattering experiments are compared with those of calculations of a structure of the mentioned solutions executed by the MonteCarlo method. It is shown that the minima of the concentration dependence of the self-diffusion coefficient correspond to certain local structures of the solution under study. Методом квазиупругого рассеяния медленных нейтронов проведено исследование динамики молекул в растворах вода—пропиловый спирт разной концентрации при температуре 281 К. Экспериментально установлены особенности концентрационной зависимости эффективного коэффициента самодиффузии и его одночастичного вклада, а именно: существование двух минимумов в областях концентрации (0,04–0,05) м.д. и (0,18–0,22) м.д. спирта, а также монотонное увеличение коэффициента диффузии при концентрациях спирта, больших чем 0,4 м.д. Результаты нейтронного эксперимента сравнивали с расчетами структуры указанных растворов, проведенных методом Монте-Карло. Показано, что минимумы в концентрационной зависимости коэффициента самодиффузии отвечают определенным локальным структурам исследуемого раствора. 2010 Article Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт / Л.А. Булавін, Н.О. Атамась, О.А. Василькевич, Г.М. Вербінська, В.І. Слісенко, О.В. Ковальов // Український фізичний журнал. — 2010. — Т. 55, № 6. — С. 694-698. — Бібліогр.: 7 назв. — укр. 2071-0194 PACS 61 https://nasplib.isofts.kiev.ua/handle/123456789/56218 538 uk Український фізичний журнал application/pdf application/pdf Відділення фізики і астрономії НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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| language |
Ukrainian |
| topic |
М'яка речовина М'яка речовина |
| spellingShingle |
М'яка речовина М'яка речовина Булавін, Л.А. Атамась, Н.О. Василькевич, О.А. Вербінська, Г.М. Слісенко, В.І. Ковальов, О.В. Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт Український фізичний журнал |
| description |
Методом квазiпружного розсiяння повiльних нейтронiв проведено дослiдження динамiки молекул розчинiв вода–пропиловий спирт рiзної концентрацiї при температурi 281 К. Експериментально виявлено особливостi концентрацiйної залежностi ефективного коефiцiєнта самодифузiї та його одночастинкового внеску, а саме: наявнiсть двох мiнiмумiв в областях концентрацiй (0,04–0,05) м.д. i (0,18–0,22) м.д. спирту та монотонне зростання коефiцiєнта дифузiї при концентрацiях, бiльших за 0,4 м.д. спирту. Результати нейтронного експерименту зiставлено з розрахунками структури указаних розчинiв, проведених методом Монте-Карло. Показано, що мiнiмуми у концентрацiйнiй залежностi коефiцiєнта самодифузiї вiдповiдають певним локальним структурам дослiдженого розчину. |
| format |
Article |
| author |
Булавін, Л.А. Атамась, Н.О. Василькевич, О.А. Вербінська, Г.М. Слісенко, В.І. Ковальов, О.В. |
| author_facet |
Булавін, Л.А. Атамась, Н.О. Василькевич, О.А. Вербінська, Г.М. Слісенко, В.І. Ковальов, О.В. |
| author_sort |
Булавін, Л.А. |
| title |
Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт |
| title_short |
Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт |
| title_full |
Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт |
| title_fullStr |
Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт |
| title_full_unstemmed |
Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт |
| title_sort |
концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт |
| publisher |
Відділення фізики і астрономії НАН України |
| publishDate |
2010 |
| topic_facet |
М'яка речовина |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/56218 |
| citation_txt |
Концентраційні особливості динаміки молекул розчинів вода−пропиловий спирт / Л.А. Булавін, Н.О. Атамась, О.А. Василькевич, Г.М. Вербінська, В.І. Слісенко, О.В. Ковальов // Український фізичний журнал. — 2010. — Т. 55, № 6. — С. 694-698. — Бібліогр.: 7 назв. — укр. |
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Український фізичний журнал |
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L.A. BULAVIN, N.A. ATAMAS’, A.A. VASILKEVICH et al.
CONCENTRATION SPECIFIC FEATURES
OF THE DYNAMICS OF MOLECULES
IN SOLUTIONS WATER–PROPYL
ALCOHOL
L.A. BULAVIN,1 N.A. ATAMAS’,1 A.A. VASILKEVICH,2
G.N. VERBINSKAYA,2 V.I. SLISENKO,2 A.V. KOVAL’OV2
1Taras Shevchenko National University of Kyiv, Faculty of Physics
(6, Academician Glushkov Ave., Kyiv 03022, Ukraine)
2Institute of Nuclear Research, Nat. Acad. of Sci. of Ukraine
(47, Nauky Ave., Kyiv 03680, Ukraine)
PACS 61
c©2010
By the method of quasielastic scattering of slow neutrons, we study
the dynamics of molecules in water–propyl alcohol solutions of var-
ious concentrations at a temperature of 281 K. In experiments,
we registered specific features of the concentration dependence
of the efficient self-diffusion coefficient and its one-particle con-
tribution, namely: the presence of two minima in the regions of
(0.04÷0.05) mass fractions (m.f.) and (0.18÷0.22) m.f. of alcohol
and a monotonous increase of the diffusion coefficient at concen-
trations greater than 0.4 m.f. of alcohol. The results of neutron-
scattering experiments are compared with those of calculations of
a structure of the mentioned solutions executed by the Monte-
Carlo method. It is shown that the minima of the concentration
dependence of the self-diffusion coefficient correspond to certain
local structures of the solution under study.
Water is a specific fluid with regard for its chemico-
physical properties. As known, these properties influ-
ence the behavior of water at its interaction with other
substances. The water structure depends on the pres-
ence of hydrogen bonds which are formed due to a spe-
cific distribution of the charge density in a molecule. At
the present time, there is no commonly accepted idea of
the water structure, which does not allow one to describe
all anomalous phenomena observed at the formation of
water solutions (in particular, alcohol-water solutions)
in a wide interval of thermodynamical parameters. Up
to now, a great number of experiments on the study
of properties of alcohol-water solutions as functions of
their concentration and the temperature were carried
out. Within the method of light scattering in water–
alcohol solutions, the maximum of the integral scatter-
ing intensity was observed [1] at the content of alcohol
x ≈ (0.15÷ 0.5) m.f. This maximum is named a normal
peak. It is well described by the theory of light scat-
tering by fluctuations of the concentration. In addition,
one more peak, besides the normal one, was discovered
at an alcohol concentration of (0.03÷0.05) m.f. in water–
alcohol solutions [1]. To explain the anomalous behavior
of water–alcohol solutions, we may use the model of mi-
croinhomogeneous cluster structure proposed in [2] for
a glycerin – water system. The assumptions about the
composition and the sizes of clusters which were made
by the authors with the use of the stability condition for
clusters are confirmed by estimates following from the
thermodynamical calculations. As for water–alcohol so-
lutions, their cluster structure at certain concentrations
is corroborated by Monte-Carlo calculations performed
for a water—ethyl alcohol solution [3, 4]. In this case,
the concentration regions of solutions characterized by
certain structural peculiarities are determined.
It is clear that the above-mentioned structural pecu-
liarities of water–alcohol solutions must affect the dy-
namics of their molecules. Therefore, within the method
of quasielastic scattering of slow neutrons (QSSN) [5],
we have studied the self-diffusion of molecules in water–
propyl alcohol solutions. As known, the QSSN method
is especially sensitive to the dynamics of molecules in
hydrogen-containing fluids and allows one to observe
the diffusion motion of molecules during the time in-
terval (10−10 ÷ 10−12 s) and, thus, to obtain the infor-
mation about the collective and one-particle motions of
molecules.
The measurement of the quasielastic scattering spec-
tra of slow neutrons was carried out on a many-detector
time-of-flight spectrometer positioned at a VVR-M re-
actor at the Institute of Nuclear Research of the NAS of
Ukraine in the scattering angle interval 25.1◦ ÷ 101.3◦.
In experiments, we used monochromatic neutrons with
an energy of 13.2 meV. We have studied the scattering
of neutrons in water–propyl alcohol solutions in a wide
694 ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 6
CONCENTRATION SPECIFIC FEATURES OF THE DYNAMICS
range of concentrations at a temperature of 281 K. In
this case, we used thin specimens, in which the neutron
flight length does not exceed 1 mm, which allowed us
to neglect the corrections for the multiple scattering of
neutrons. The obtained spectra of quasielastic scatter-
ing of neutrons with regard for the resolving power of a
spectrometer were approximated by the Lorentz function
S(Q, ε) =
exp(−2W ) 2~ ΔE(Q)
π
(
ε2 + ΔE (Q)2
) (1)
describing the quasielastic scattering of neutrons,
exp{−2W} is the Debye–Waller factor, ε = ~ω is a
change of the neutron energy at the scattering, Q =
k − k0 is a change of the wave vector of a neutron in
the process of scattering, and ΔE (Q) is a half-width
of the quasielastic peak. By using the method of least
squares, we approximated the quasielastic peak of scat-
tered neutrons by function (1). As a result, we obtain
the functional dependence ΔE
(
Q2
)
containing the full
information about the diffusion processes in the fluid sys-
tem under study. In more details, the procedure of cal-
culations is given in [5].
In the analysis of the dependences ΔE
(
Q2
)
obtained
on the basis of neutron spectra, we applied the Bulavin–
Oskots’kyi–Ivanov model [6] which considers most com-
pletely the diffusion motions of molecules such as the
oscillations of molecules around a center of temporary
equilibrium, the hops of molecules from one center of
equilibrium to another one (the so-called Frenkel mech-
anism of diffusion), and the diffusion of centers of equi-
librium (the so-called Lagrange mechanism of diffusion).
In the frame of this model, the widening of the peak is
described by the formula
ΔE = 2 ~DLQ
2 +
2~
τ0
[
1− exp {−2W}
1 +Q2(D −DL)τ0
]
, (2)
where D is the total self-diffusion coefficient, DL is the
coefficient of continuous (Lagrange) diffusion of the cen-
ters of oscillations of molecules, and τ0 is the duration
of the settled life of a molecule in the position of equilib-
rium between two hops. In order to determine the pa-
rameters D,DL, and τ0, the experimental dependences
ΔE = ΔE(Q2) at a constant concentration of the solu-
tion were approximated by the theoretical curve (2) in
the whole interval of variations of the square of the wave
vector transferred.
The use of the conception of a hierarchy of the time
scales of molecular motions [7] allows us to separate the
self-diffusion coefficient D into the collective (Lagrange)
Fig. 1. Concentration dependence of the self-diffusion coefficient
D, its collective DL and one-particle DF contributions. X is the
concentration of propyl alcohol in a water solution
DL and one-particle (Frenkel) DF parts:
D = DL +DF . (3)
The experimental concentration dependences of the self-
diffusion coefficient D and its components DL and DF
are given in Fig. 1.
It is seen from Fig. 1 that the concentration de-
pendences of the effective self-diffusion coefficient D
of molecules of a propanol–water solution and its one-
particle component DF have two minima, respectively,
at the concentrations of alcohol x = (0.04 ÷ 0.05) m.f.
and x = (0.18 ÷ 0.22) m.f., which testifies to a signifi-
cant deceleration of diffusion motions and a decrease in
the one-particle contribution at the indicated concentra-
tions. The minimum at a higher concentration of alcohol
has a greater width and corresponds to the scattering of
neutrons by fluctuations of the concentration.
It is worth noting that the scattering cross-section of
slow neutrons by hydrogen atoms is more approximately
by a factor of 20 than those by the other atoms. This
implies that neutrons “feel” mainly the motions of hy-
drogen atoms in molecules of alcohol and water con-
taining hydrogen and, therefore, give information about
the fluid dynamics only to that extent, at which this
dynamics is reflected in motions of these atoms. At
a concentration of 0.04 m.f. of propyl alcohol in wa-
ter, the ratio of protons in alcohol molecules and wa-
ter molecules amounts to 1:6. Hence, neutrons reflect
mainly the dynamics of water molecules in a solution.
But, at a concentration of 0.2 m.f. of alcohol, the num-
bers of protons in molecules of alcohol and water are
ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 6 695
L.A. BULAVIN, N.A. ATAMAS’, A.A. VASILKEVICH et al.
Fig. 2. Dependence of the duration of the settled life of molecules
in the position of equilibrium on the concentration of alcohol in
water–propanol solutions
the same. In this case, the contributions to the widen-
ing of the quasielastic peak from motions of molecules
of alcohol and water are almost identical. In the in-
terval of concentrations x = (0.18 ÷ 0.22) m.f. of al-
cohol, the collective component DL of the self-diffusion
coefficient attains a minimum value and then monoton-
ically increases. The monotonous increase of the total
self-diffusion coefficient and its components is charac-
teristic at concentrations more than 0.4 m.f. of alco-
hol.
Based on the experimental data on the quasielastic
scattering of slow neutrons and relation (2), we made
attempt to evaluate the mean duration of the stay of
molecules in the position of equilibrium. As seen from
Fig. 2, the concentration dependence of the duration of
the settled life of molecules τ0 in the position of equilib-
rium has a maximum in the alcohol concentration region
x = (0.04 ÷ 0.05) m.f. and a wide maximum in the re-
gion of concentrations x = (0.18÷ 0.22) m.f. of alcohol.
Such significant increase in the duration of the settled
life indicates a local structural reconstruction of solu-
tions at the indicated concentrations, and the widths
of maxima demonstrates the fundamental difference of
mechanisms of these processes for two given concentra-
tions.
A significant deceleration of diffusion motions and an
increase in the duration of the settled life in the indicated
region of concentrations (Figs. 1 and 2) are related, in
our opinion, to the formation of stable water–alcohol
complexes.
Such a behavior of the self-diffusion coefficient and
the duration of the settled life at a change of the solu-
tion concentration become understandable if we com-
pare the results of neutron experiments to those ob-
tained by us within the Monte-Carlo method for the
structure of water — propyl alcohol solutions. As a re-
sult of the computer simulation, we obtained the depen-
dences of the mean energies of components of the in-
termolecular interaction (the interaction between water
molecules, the interaction between molecules of alcohol,
and the interaction between water molecules and alco-
hol), the radial distribution functions, and the numbers
of the nearest neighbors. On the basis of the data ob-
tained, we have determined the regions, where the local
structure of a solution varies, and propose the model
ideas for the description of a structure of the water–
propyl alcohol system under study at various concentra-
tions.
According to the calculations, we can separate several
regions of concentrations of water–alcohol solutions with
a local structure characteristic of each region.
1. Concentration of Propyl Alcohol in a Water
Solution with x < 0.04 m.f.
The introduction of propanol molecules into water in this
region of concentrations does not lead to breaks in the
network of hydrogen bonds which is formed by water
molecules. A propanol molecule introduced into a solu-
tion is surrounded by (7 ÷ 8) water molecules, and the
interaction between molecules of propanol at large dis-
tances does not cause the formation of complexes with
molecules of alcohol. In this region of concentrations, the
water clusters are composed of 6 molecules of water. In
this case, the self-diffusion coefficient of water molecules
in the alcohol solution is close to the self-diffusion coef-
ficient of pure water.
2. Concentration of Propyl Alcohol in a Water
Solution with x ∼ (0.04 ÷ 0.1) m.f.
In the limits of this region of concentrations, there oc-
curs a reconstruction of water clusters and a decrease
in the number of molecules in them to five. Complexes
which are composed of at least one water molecule and
one propanol molecule are formed. At the same time,
there exist the systems including one propanol molecule
surrounded by (7÷8) water molecules.
The formation of complexes of water molecules and
alcohol leads to a significant deceleration of the diffu-
sion motion and an increase in the duration of a set-
tled life of water molecules in a position of equilib-
rium. This explains the presence of the minimum in
696 ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 6
CONCENTRATION SPECIFIC FEATURES OF THE DYNAMICS
the concentration dependence of the self-diffusion coef-
ficient D and its one-particle contribution DF , as well
as the presence of the maximum of τ0 at concentrations
x = (0.04÷0.05) m.f., which was observed in the neutron
experiments.
3. Concentration of Propyl Alcohol in a Water
Solution with x ∼ (0.1 ÷ 0.25) m.f.
In the region of concentrations x ∼ (0.1 ÷ 0.18) m.f.,
there occurs the further reconstruction of water clus-
ters and a decrease in the number of their molecules to
four. As a result, the systems composed of two water
molecules and, as a minimum, one propanol molecule
are formed. In addition, we assume the presence of sys-
tems including a single water molecule and one propanol
molecule, as well as systems of (7÷8) water molecules
surrounding a single propanol molecule.
As a concentration x ∼ (0.18÷ 0.22) m.f. is attained,
we can assume the formation of clusters of six propanol
molecules surrounded by (18-20) water molecules due to
the hydrophobic interaction of propanol molecules be-
tween themselves and the interaction between molecules
of water and propanol. In the limits of concentrations
x ∼ (0.18 ÷ 0.25) m.f., the systems composed of water
molecules surrounding one propanol molecule continue
to exist. These systems are analogous to those which
are registered in infinitely diluted solutions.
In the region of concentrations x ∼ (0.18÷ 0.22) m.f.
of alcohol, the data of neutron experiments on the con-
centration dependence of the coefficient self-diffusion D
and its one-particle component DF indicate the pres-
ence of the second wider minimum and maximum of the
concentration dependence τ0.
4. Concentration of Propyl Alcohol in a Water
Solution with x ∼ (0.25 ÷ 0.4) m.f.
In the limits of this region of concentrations, there oc-
curs the formation of a structure of clusters of propanol
molecules. Near concentrations greater than x ∼ 0.3
m.f., these clusters include four propanol molecules sur-
rounded by eight water molecules. In this case, two wa-
ter molecules are present in the vicinity of an alkyl chain
of propanol molecules, and a single water molecule is
near the hydroxyl group of a propanol molecule.
We note that, at the concentration of alcohol x ≥
0.3 m.f., the structure of clusters of propanol molecules
reminds that of micellae. The interior and exterior of
clusters contain, respectively, hydroxyl groups and alkyl
groups of propanol molecules.
5. Concentration of Propyl Alcohol in a Water
Solution with x > 0.4 m.f.
In this region of the concentration, we observe a
monotonous increase in the self-diffusion coefficient and
its components, as well as a monotonous decrease in
the duration of the settled life, as the concentration
of alcohol in water increases. The increase in the col-
lective contribution to the self-diffusion coefficient tes-
tifies that the solutions contain the centers of oscil-
lations surrounded by hydration shells. As the cen-
ters of oscillations, we may consider the micella-like
complexes formed by molecules of alcohol surrounded
by the first and second hydration shells. At the
same time, the increase in the one-particle compo-
nent of the self-diffusion coefficient with the concentra-
tion of alcohol in a solution indicates the presence of
free water molecules in solutions or temporarily liber-
ated water molecules which appear during their trans-
fer from one hydration shell to another one. Free
molecules of alcohol not bound in complexes can also
exist.
The increase in the self-diffusion coefficient and the de-
crease in the duration of the settled life of molecules in a
position of equilibrium at a further increase in the con-
centration of alcohol are a consequence of the decrease
in the number of water molecules in hydration shells,
which causes an increase in the mobility of propanol
molecules.
Thus, within the method of the quasielastic scatter-
ing slow of slow neutrons and the method of Monte-
Carlo, we have studied the influence of the concen-
tration of alcohol on a local and energy properties of
the water–propanol system. The analysis of the ob-
tained radial distribution functions in these liquid sys-
tems allowed us to separate several regions of concentra-
tions of the water–alcohol solution with a local structure
of a solution characteristic of each region. The exis-
tence of the separated regions of concentrations in the
water—propyl alcohol system is confirmed experimen-
tally by the method of quasielastic scattering of slow
neutrons. We have revealed the minima on the con-
centration dependences of the self-diffusion coefficient D
and its one-particle componentDF at the concentrations
x = (0.040 ÷ 0.05) m.f. and x = (0.18 ÷ 0.22) m.f. of
alcohol which correspond to certain local structures of a
solution.
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lutions (Leningrad State Univ., Leningrad, 1977) (in Rus-
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Received 30.12.09.
Translated from Ukrainian by V.V. Kukhtin
КОНЦЕНТРАЦIЙНI ОСОБЛИВОСТI ДИНАМIКИ
МОЛЕКУЛ РОЗЧИНIВ ВОДА—ПРОПИЛОВИЙ СПИРТ
Л.А. Булавiн, Н.О. Атамась, О.А. Василькевич,
Г.М. Вербiнская, В.I. Слiсенко, О.В. Ковальов
Р е з ю м е
Методом квазiпружного розсiяння повiльних нейтронiв
проведено дослiдження динамiки молекул розчинiв вода–
пропиловий спирт рiзної концентрацiї при температурi 281
К. Експериментально виявлено особливостi концентрацiйної
залежностi ефективного коефiцiєнта самодифузiї та його
одночастинкового внеску, а саме: наявнiсть двох мiнiмумiв в
областях концентрацiй (0,04–0,05) м.д. i (0,18–0,22) м.д. спирту
та монотонне зростання коефiцiєнта дифузiї при концентра-
цiях, бiльших за 0,4 м.д. спирту. Результати нейтронного
експерименту зiставлено з розрахунками структури указаних
розчинiв, проведених методом Монте-Карло. Показано, що мi-
нiмуми у концентрацiйнiй залежностi коефiцiєнта самодифузiї
вiдповiдають певним локальним структурам дослiдженого
розчину.
698 ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 6
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