Ultrasonic studies of intermolecular interactions in binary mixtures of 4-methoxy benzoin with various solvents: Excess molar functions of ultrasonic parameters at different concentrations and in different solvents

Article abstract of DOI:10.1016/j.ultsonch.2012.03.006

Density (ρ), ultrasonic velocity (U), for the binary mixtures of 4-methoxy benzoin (4MB) with ethanol, chloroform, acetonitrile, benzene, and di-oxane were measured at 298 K. The solute-solvent interactions and the effect of the polarity of the solvent on

Full text of DOI:10.1016/j.ultsonch.2012.03.006

Ultrasonics Sonochemistry 19 (2012) 1213–1220
Contents lists available at SciVerse ScienceDirect
Ultrasonics Sonochemistry
journal homepage: www.elsevier.com/locate/ultson
Ultrasonic studies of intermolecular interactions in binary mixtures
of 4-methoxy benzoin with various solvents: Excess molar functions
of ultrasonic parameters at different concentrations and in different solvents
B. Thanuja , G. Nithya , Charles C Kanagam b
a,
⇑
a
a
Dept. of Chemistry, Vels University, School of Engineering, Pallavaram, Chennai 600 117, Tamil Nadu, India
Dept. of Chemistry, SRM Valliammai Engineering College, Kattangalathur, Kanchipuram, Tamil Nadu, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Density (q), ultrasonic velocity (U), for the binary mixtures of 4-methoxy benzoin (4MB) with ethanol,
chloroform, acetonitrile, benzene, and di-oxane were measured at 298 K. The solute–solvent interactions
and the effect of the polarity of the solvent on the type of intermolecular interactions are discussed here.
f
From the above data, adiabatic compressibility (b), intermolecular free length (L ), acoustic impedance (Z),
apparent molar volume (Ø), relative association (RA) have been calculated. Other useful parameters such
as excess density, excess velocity and excess adiabatic compressibility have also been calculated. These
parameters were used to study the nature and extent of intermolecular interactions between component
molecules in the binary mixtures.
Received 2 September 2011
Received in revised form 17 February 2012
Accepted 13 March 2012
Available online 24 March 2012
Keywords:
Ultrasonic velocity
Density
Excess parameters
Intermolecular hydrogen bonding
Ó 2012 Elsevier B.V. All rights reserved.
1
. Introduction
The practical application of mixed solvents, rather than single
From this, ultrasonic parameters like adiabatic compressibility,
intermolecular free length and apparent molar volume were calcu-
lated using standard formulae [4]. Excess functions such as excess
adiabatic compressibility, excess velocity, excess intermolecular
free length, excess acoustic impedance, and excess apparent molar
volume were also calculated. The values are plotted against con-
centration and ultrasonic parameters. The graphs obtained are ex-
plained on the basis of the various intermolecular interactions
present in the system and how the interactions are affected by
the change of solvents and concentration.
solvents, in industrial and biologic processes has been recognized
all over the world, as they provide a wide choice of solvent mix-
tures with appropriate properties [1,2]. Experimental studies
aimed at finding evidence for intermolecular interactions in binary
liquid mixtures have been carried out by us [3]. We focus in this
paper the results of ultrasonic studies of binary mixtures of 4-
methoxy benzoin (4MB) with solvents of different polarities. The
components of these binary mixtures (4MB and various solvents)
are interesting, as they have proton donor as well as proton accept-
ing abilities. As a result, significant interaction through hydrogen
bonding between unlike molecules in these binary mixtures is ex-
pected. Also, it is worthwhile examining the effect of intermolecu-
lar interaction between 4MB and various solvents. We report here
the results of ultrasonic study of molecular interactions of 4MB at
2
. Experimental
The solvents ethanol, acetonitrile, chloroform and benzene
(
S.D. Fine, India, AR) were dried over molecular sieves. All the
solutions were prepared by weighing in a dry bottle and were
kept in special air tight bottles. 4MB was prepared by the crossed
benzoin condensation of benzaldehyde with 4-methoxy benzalde-
hyde. The molecular structure and conformation were confirmed
using single-crystal XRD studies (Fig. 1). Solutions of different
mole percent of 4MB with various solvents, were prepared at
room temperature. All of them were allowed to attain constant
temperature in a constant temperature bath, before carrying out
the experiment. The densities of solutions were measured using
2
98 K in ethanol, chloroform, acetonitrile, benzene, dioxane binary
mixtures. Ethanol is a highly polar but protic solvent. In the liquid
state its molecules are associated through hydrogen-bonding. The
solvent polarity decreases from ethanol to benzene. The intermo-
lecular interaction varies from polar solvent to non-polar solvent.
Density, viscosity and ultrasonic velocity were experimentally
determined for 4MB/solvent systems of different concentrations.
ꢁ6
3
a pycnometer of bulb capacity 8 ꢀ 10 m with a graduated stem
ꢁ
8
3
⇑
Corresponding author.
E-mail address: revasuku25@gmail.com (B. Thanuja).
with 5 ꢀ 10
m divisions (Systronies India, Ltd.). The marks on
the stem were calibrated using double-distiled water of known
1
350-4177/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ultsonch.2012.03.006

1
214
B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
Fig. 1. The ortep diagram for 4-methoxy benzoin.
densities. The accuracy of the density measurement was found to
be 0.001 g/cc. The viscosities of the binary mixtures were deter-
mined using an Ostwald Viscometer (Sigma Chemicals and Instru-
ments). The ultrasonic velocities of pure solvent and the binary
mixtures were measured using a single crystal variable path
interferometer at 2 MHz (Mittal Enterprises, New Delhi). The
accuracy in the ultrasonic velocity was found to be ±0.05ꢀ. The
temperature of the test liquids was maintained to an accuracy
of ±0.02° in an electrically controlled thermostatic water bath.
From the measured density, viscosity and ultrasonic velocity U,
binary mixtures can be proposed. A decrease in the density of a
solution with dilution is the expected trend [5,6]. For the system
of 4MB and different solvents under study, there is a decrease in
density at low concentration region for polar solvents like ethanol,
acetonitrile, 1,4-dioxane and there is a initial increase in density
(Fig. 2) for non-polar solvents viz chloroform and benzene. As
the polarity of the solvent decreases at the concentration of
0.05 molꢀ, there is a decrease in density. Beyond the concentration
of 0.05 molꢀ, there is small increase in density, increasing with
concentration for the non-polar solvent. In the case of polar sol-
vents, the increase in density is more significant. As the polarity
of the solvent decreases, there is an increase in density. The initial
sharp decrease in density can be explained on the basis of a sudden
increase in the volume of the solution with the addition of 4MB.
Polar protic solvents are associated in the pure state through inter-
actions such as intermolecular hydrogen bonding and dipole–di-
pole attraction. Addition of 4MB leads to the breakdown of the
hydrogen bonds, releasing the dipoles of polar solvent. As a result,
the free dipoles of solvents interact with 4MB molecules, forming
intermolecular hydrogen bonds. Incorporation of large solute mol-
ecules in the solvent leads to an increase in the volume of solution.
This is seen in the initial slow decrease in density of solution of po-
lar solvents. At higher concentrations, the solute–solvent interac-
tions are slowly replaced by the solute/solute interactions.
Increase in density can be attributed to the solute/solvent intermo-
lecular interactions. The small increase in the case of non-polar sol-
vents is attributed to the weak dipole-induced dipole attractions
between the non-polar solvent and solute molecules. Beyond
the adiabatic compressibility, b or K
s
, intermolecular free length
f
L , relative association RA, and acoustic impedance Z, were calcu-
lated using the following relations.
2
b ¼ K
s
¼ 1=u
q
ð1Þ
ð2Þ
1
=2
L
f
¼ K=u
q
ꢂ
ꢂ
1=3
RA ¼ ð
q
=q
Þ ꢀ ðu =uÞ
ð3Þ
ð4Þ
Z ¼ uq
where
K
is
a
temperature-dependent constant (93.875 +
ꢁ
8
0
.375 ꢀ T) ꢀ 10 , T is the absolute temperature, Z is the acoustic
impedance, K the adiabatic compressibility, L the intermolecular
free length, RA is the relative association, and
s
f
o
q , q, u°, and u are
the densities and ultrasonic velocities of the solvent and solution
respectively. The excess functions for each of the ultrasonic param-
eter were calculated using the following formula.
0
.18 molꢀ there seems to be an increase in the density of the solu-
tion in non-polar solvent. This can be explained by the fact that as
the concentration increases, the dipole-induced dipole attractions
also increase, leading to a decrease in volume. In the case of etha-
nolic solutions, there is found to be a continuous increase in the
density of the solution with an increase in concentration. This is
attributed to the presence of strong intermolecular attraction such
as dipole–dipole attraction and hydrogen bonding. In the case of
acetonitrile the increase in concentration results in the preferential
formation of intermolecular hydrogen bonding between the solute
molecules, forming a well-arranged structure, leading to an in-
crease in the volume of the solution, which leads to a decrease in
density. An increase in concentration allows for a closer approach
of solvent and solute molecules, and stronger association between
solute and solvent molecules [7,8]. This leads to a decrease in the
E
f
¼ Eexpt ꢁ Eideal
ð5Þ
1
2
E
ideal ¼ ½xy þ ð1 ꢁ xÞy ꢃ
ð6Þ
1
2
where y and y are the ultrasonic parameters of pure solvent and
solution respectively. The values of , u, K , and L as a function of
mole fraction x of various solvents (ethanol, acetonitrile, chloro-
q
s
f
form, benzene, dioxane) at 298 K are presented in Table A.1.
3
. Results and discussion
From the variation of densities, viscosities and ultrasonic
parameters with concentration and temperature, a qualitative
interpretation of the intermolecular interactions in the above

B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
1215
Table A.1
Values of density, q, ultrasonic velocity, u, adiabatic compressibility, b, intermolecular freelength, Lf, relative association RA and excess functions of binary mixtures as a function
of concentration (molꢀ) using various solvents.
Solvents
Concentration for various ultrasonic parameters
ꢁ
1
Velocity ms
0.000562
931.2
Non-Ideal (NI)
Ethanol
Chloroform
Acetonitrile
Benzene
0.001125
2556.8
936
1326.4
1588.8
2284.8
0.00225
1427.2
948
1187.2
1348.8
1276.8
0.0045
1240.8
1806.4
1424.8
1435.2
1574.4
0.09
0.018
1070.4
1115.2
1209.6
1532.8
1311.2
2109
840
1185.6
1318.4
1294.4
1161.6
1003.2
1247.2
1
,4-Dioxane
ꢁ
3
Non-Ideal (NI)
Ethanol
Density Kgm
767
768
1440
761
774
1407
761
779
1310
763
782
1306
762
Chloroform
Acetonitrile
Benzene
1445
759
864
1356
761
857
857
856
856
851
1
,4-Dioxane
1007
1006
1007
996
1006
1009
ꢁ
1
2
Non-Ideal (NI)
Ethanol
Chloroform
Acetonitrile
Benzene
Adiabatic compressibility (kg ms )
15
1.5
1.9
7.9
7.4
4.6
1.9
6.3
7.9
9.3
6.4
6.0
8.3
2.3
6.4
5.6
4.0
11.1
8.9
8.9
5.0
5.7
9.7
9.7
11.5
5.4
9.3
6.6
5.9
1
,4-Dioxane
0
Non-Ideal (NI)
Ethanol
Chloroform
Acetonitrile
Benzene
Intermolecular freelength A
7.9732
2.564
6.2953
5.3060
5.00602
2.9020
5.789
5.619
4.42095
2.83745
5.1787
5.9375
6.8695
6.2786
6.2786
5.21064
5.07502
5.2248
5.2248
4.89696
4.1383
6.1582
6.1582
4.5986
4.9443
6.4169
6.4169
7.00161
4.8051
1
,4-Dioxane
Non-Ideal (NI)
Ethanol
Chloroform
Acetonitrile
Benzene
Relative association (RA)
1.957
0.716709
1.00611
0.93047
0.93535
0.8475
1.70083
0.97933
0.961417
0.98130
1.058411
0.90306
0.75146
0.9131027
0.96319
0.93826
0.947626
0.749166
0.957819
0.938854
1.00114
0.79126
0.95994
0.99727
1.006024
0.97871
0.96825
1.07369
0.99600
1
,4-Dioxane
Excess velocity
Ethanol
ꢁ165.5264
1455.032
ꢁ18.0336
3.93853
307.50562
921.72634
334.773
159.7935
160.8024
9.898402
169.70302
227.3208
13.5507
433.50576
200.54185
280.24680
39.4513
Chloroform
Acetonitrile
Benzene
ꢁ28.5485
840.93473
6.165494
72.31036
ꢁ76.7731
ꢁ64.93
1.243081
34.55288
ꢁ67.79197
207.139
ꢁ186.99
61.4156
1
,4-Dioxane
Excess density
ꢁ63.0221
2.68394
2.915808
5.75823
ꢁ6.3225
Ethanol
ꢁ60.34468
ꢁ4.46227
5.82226
.496563
ꢁ7.01260
ꢁ49.2777
ꢁ27.033
7.65272
2.93079
2.06342
ꢁ37.79392
ꢁ111.8056
13.250905
9.75025
ꢁ16.3076
ꢁ93.1748
19.42742
18.68965
20.05802
Chloroform
Acetonitrile
Benzene
ꢁ2.7125
32.1465
49.5255
52.065
1
,4-Dioxane
ꢁ5.07932
Excess adiabatic compressibility
Ethanol
5.10597
ꢁ11.80336
0.49093
ꢁ3.40134
0.54842
0.90924
ꢁ0.3628
0.75635
ꢁ1.2433006
ꢁ5.07623
ꢁ1.96694
ꢁ1.0923
1.71672
ꢁ1.05773
0.16171
ꢁ1.5402
0.5676
Chloroform
Acetonitrile
Benzene
ꢁ5.88525
0.011281
ꢁ0.20716
0.62967
3.23862
ꢁ2.6448
4.8098
ꢁ1.00949
ꢁ2.1846
1
,4-Dioxane
ꢁ3.34525
ꢁ1.1783
0.4234
Excess intermolecular free length
Ethanol
1.5196
ꢁ3.50786
0.19469
0.03594
ꢁ1.1836
0.22528
0.705414
ꢁ0.115082
0.38452
ꢁ0.31992
ꢁ2.40121
ꢁ0.32205
0.08626
0.765506
ꢁ0.318915
0.64682
Chloroform
Acetonitrile
Benzene
ꢁ3.02766
0.70395
ꢁ0.05365
0.2890
1.30609
0.99808
1.8602
ꢁ0.931923
ꢁ0.571995
1
,4-Dioxane
ꢁ1.8758
ꢁ0.5045
0.35608
0.35290
Excess acoustic impedance
Ethanol
Chloroform
Acetonitrile
Benzene
ꢁ0.26085
1.65058
ꢁ0.04668
0.018599
ꢁ0.08216
1.05089
ꢁ0.04790
0.00229
0.24239
0.912358
0.2019710
ꢁ2.71949
ꢁ0.03949
0.041105
ꢁ0.0907
0.079710
0.976197
0.14716
0.124036
0.198652
0.024307
0.10214
ꢁ0.007367
0.224048
ꢁ0.02908
ꢁ0.1643
0.02596
ꢁ0.2103
0.08015
1
,4-Dioxane
volume and an increase in the density of the solution. Beyond the
concentration of 0.005 molꢀ a decrease in density is observed for
ethanol with an increase in concentration. This can be explained
by an increase in the disruption of the intermolecular hydrogen
bonding between solute molecules by the comparatively weaker
solute/solvent interactions. For the non-polar solvent benzene, be-
yond 0.005 molꢀ a sharp decrease in density is observed because
the larger solute molecules with intermolecular hydrogen bonding
network have to be accommodated in the solvent structure with-
out any strong interaction.

1
216
B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
Fig. 2. Density (Kg m 3) vs concentration (molꢀ).
ꢁ
Fig. 3. Velocity (ms 1) vs concentration (molꢀ).
ꢁ
The ultrasonic velocity is found to be lowest at very low concen-
replacement of strong intermolecular attraction between solvent
molecules by the weaker intermolecular interactions. This indi-
cates that the solvent–solvent interaction is replaced by solute–
solvent interaction even at the low concentration. Generally, adia-
batic compressibility decreases with increase in concentration [9].
A high value of adiabatic compressibility for the low concentration
of polar solvent (0.000625 molꢀ) indicates a positive solute–
solvent interaction, and at the same time the network of hydrogen
bonding formed by the solvent molecules is not much disturbed.
The decrease in adiabatic compressibility with further increase in
concentration indicates the breakdown of the network formed by
the solvent molecules. Adiabatic compressibility reaches a mini-
mum at 0.001125 molꢀ. Beyond this concentration there is an in-
crease in the adiabatic compressibility with an increase in
concentration. This indicates that the solute/solvent interaction is
tration and the increase in ultrasonic velocity with increase in con-
centration is an expected trend [9]. Beginning with a concentration
of 0.000625 molꢀ, there is sharp increase in velocity with increase
in concentration, reaching a maximum followed by a decrease
(
Fig. 3). The increase of ultrasonic velocity from 0.000625 molꢀ
concentration indicates the formation of strong hydrogen bonds
of the polar solvent molecules with the larger benzoin molecules.
An opposite trend is observed in the adiabatic compressibility
(
Fig. 4). A similar explanation for the decrease in compressibity
with concentration of the liquid mixtures has been suggested by
Fork and Moore [10]. The maximum in ultrasonic velocity is ob-
served at 0.0012 molꢀ concentration. The decrease in ultrasonic
velocity indicates that the interaction between solute (solute mol-
ecule) and solvent is becoming less dominant. This is due to the

B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
1217
Fig. 4. Adiabatic compressibility (kg 1 ms ) vs concentration (molꢀ).
ꢁ
2
replaced by comparatively stronger interaction between solute
molecules, releasing the solvent molecules. Further increase in adi-
abatic compressibility indicates a change in the conformation /ori-
entation of the solute molecules in solution, leading to weaker
inter-molecular interaction. This is attributed to the steric require-
ment of arranging an increasing number of larger molecules. In this
situation, the steric factor takes predominance over intermolecular
interactions. The changes in acoustic impedance are expected to be
similar to those of ultrasonic velocity. The maximum is shifted
from 0.001125 molꢀ. An increase in adiabatic compressibility indi-
cates a change in the arrangement of the solvent molecules around
the solute molecule undergoing conformational change, which re-
sults in weakening of the solute/solvent interactions. This means
that the solution becomes more compressible. It also indicates
the associating tendency of the solute molecules in solution.
Intermolecular free length and adiabatic compressibility are di-
rectly related to each other [11,12]. Hence, the adiabatic compress-
ibility increases with an increase in intermolecular free length. The
ꢁ
11
Fig. 5. Intermolecularfreelength (10
m) vs concentration (molꢀ).
Fig. 6. Relative association vs concentration (molꢀ).

1
218
B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
of intermolecular free length with increase in concentration is a
normal trend [13]. The initial rise in intermolecular free length
indicates that weak forces are acting between solute and solvent
molecules, forming loosely held aggregates. The decrease in free
length can be attributed to an increase in the stronger forces of
cohesion between solute and solvent molecules. The initial in-
crease of free length with an increase in molar concentration
shows the reduction in the degree of association among solvent
molecules. This is due to the loss of dipolar association; breaking
up of hydrogen bonds and differences in the size and shapes of
molecules in the liquid mixtures [14,15].
1
3
The relative association, RA, is directly proportional to
q
/
U
.
This is influenced by two factors:
i) The breaking up of solvent/solvent interaction on addition of
solute Indicates higher value of RA.
ii) Solvation of solute indicates a lower value of RA⁄10.
ꢁ
1
2
Fig. 7. Excess adiabatic compressibility (kg ms ) vs concentration (molꢀ).
Relative association is found to have an initial minimum value
at 0.001125 molꢀ for polar solvent. Beyond this concentration,
the RA values increases, reaching a maximum at 0.18 molꢀ. The
maxima and minima are shifted to low concentration regions of
stronger intermolecular interactions results in a tightly packed li-
quid structure, and, as such, the adiabatic compressibility and
intermolecular free length decrease. The formation of weaker
intermolecular interaction leads to an increase in adiabatic com-
pressibility and intermolecular free length. The intermolecular free
length and ultrasonic velocity are inversely related to each other
0
4
.18 and 0.001125 molꢀ, respectively. Further, the addition of
MB does not affect the existing intermolecular interactions signif-
icantly. This trend can be explained in that at low concentration,
the solvent/solvent interactions break down to give way to sol-
vent/solute (Fig. 6) interactions. In the concentration range of
[
5,6]. The ultrasonic velocity increases with a decrease in the inter-
0
.009–0.18 molꢀ, there is a sharp decrease in apparent molar vol-
molecular free length. There is an initial increase in intermolecular
free length in the low concentration region, followed by a steady
decrease with an increase of concentration (Fig. 5). The decrease
ume for polar solvent as the concentration increases. This clearly
shows that within the concentration range a significant solute–
Fig. 8. Excess intermolecular freelength A0 vs concentration (molꢀ).
Fig. 9. Excess velocity ms 1 vs concentration (molꢀ).
ꢁ

B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
1219
solvent interaction is taking place. Beyond this concentration
range, the decrease in molar volume is not very significant. As
the polarity of the solvents decrease, there is a slight increase in
apparent molar volume at concentration 0.00225 molꢀ. This is ex-
plained as the increase in concentration allows for closer approach
of solvent and solute molecules and stronger association between
solute and solvent molecules. This leads to decrease in volume
and an increase in the density of the solution. The strength of inter-
action between component molecules is well reflected in devia-
dipole–dipole, dipole-induced dipole and hydrogen bonding inter-
actions between the solute and solvent. The type and the magni-
tude of interaction depend on the polarity of the solvents and
concentration of the solute.
Acknowledgements
The author acknowledges Vels University for providing the lab
facilities and for giving the opportunity to do the research work.
The author further acknowledges Prof. Vargese, and Mr. Jagan,
Central Instrumentation Center, IIT, Chennai, for single-crystal
XRD studies and the faculty of the Chemistry department of SRM
Valliammai Engineering College for useful discussion.
s f
tions observed in K , q, U, and L from the expected trend. The
excess parameters are found to be more sensitive towards inter-
molecular interactions in the binary mixture.
4
. Conclusions
Appendix A. Supplementary material
In polar protic solvents, molecules are held together by com-
paratively strong hydrogen bonds forming a network. A Polar sol-
vent is capable of taking part in dipole–dipole, dipole-induced
dipole and hydrogen bonding interactions between themselves,
which are being slowly replaced by solvent–solute interaction
when a solute is added. This leads to the solvation of the solute
molecules, resulting in an increase in volume and a decrease in
density of the mixture. In non-polar solvents at higher concentra-
tion the dipole-induced dipole interaction is increased by the
added solute molecules leading to decrease in volume. The study
of ultrasonic parameters and excess functions for the binary mix-
ture of 4MB with different solvents at various concentrations
indicate that there are intermolecular interactions such as
CCDC 816871 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge at
www.ccdc.ac.uk/conts/retrieving.html (or from Cambridge Crystal-
lographic Data Center (CCDC), 12 Union Road, Cambridge CB2 IEZ,
UK +44 (0) 1223 336033; e-mail:deposit@ccdc.cam.ac.uk).
Appendix B. Excess functions
An ideal solution should be considered as non-associated and
for an ideal mixture the values of excess property is zero. For
non-ideal mixtures, the difference between experimental values
and ideal values is significant. Excess functions were calculated
using the general formula [16]. For ideal binary mixtures:
Exc
I
Exp
I
Y
= Y ꢁY = 0
Exp
Y = Y
In general for non-ideal mixtures:
Exc
I
Exp
I
Y
= Y ꢁY
Y = (1 ꢁ x)Y
o s
+ (x)Y
Exc
Y
Y
= excess function
Exp
I
= experimental value
Y = ideal value
x = mole fraction of solute
Y
Y
o
= value for pure solvent
= value for solution
s
For non ideal mixtures, depending upon the magnitude and
type of intermolecular interactions or changes in concentration
and orientation of solute molecules in solution, the magnitude
and the sign of the excess values also change.
6
ꢁ2
Fig. 10. Excess acoustic impedance (Z ꢀ 10 Kg ms /S) vs concentration (molꢀ).
3
Fig. 11. Excess density (kg/m ) vs concentration (molꢀ).

1
220
B. Thanuja et al. / Ultrasonics Sonochemistry 19 (2012) 1213–1220
Excess functions are calculated by following the literature pro-
cedures reported [17–19]. The negative values of excess adiabatic
compressibility (Fig. 7) and excess inter molecular free length
may be attributed to specific, strong interactions like hydrogen
bonding and dipole–dipole interactions, while the negative devia-
tions may be ascribed to weak dispersion forces in the system.
(Fig. 8), in the concentration range of 0.001125–0.0045 for polar
Oswal and Desaih [16,20] attributed the positive excess of K
s
and
solvents and 0.000526–0.009 for non-polar solvents and a positive
excess velocity at higher concentration for polar solvent and at low
concentration for non-polar solvent suggest that either a strong
intermolecular interaction or a change in conformation or orienta-
tion of molecules taking place in solution, resulting in the forma-
tion of a more compact structure due to hydrogen bonding
between unlike molecules (Fig. 9). The positive values of excess
adiabatic compressibility, excess intermolecular free length, and
negative excess velocity, indicate weaker interactions between sol-
ute and solvent molecules, resulting from the disruption of molec-
ular association. When excess volumes are negative for all
concentrations, the existence of interactions between solute and
solvent molecules is apparent. A positive excess acoustic imped-
ance value indicates that over the concentration range of
L
f
values to the large size of the solute molecules and weaker cohe-
sive forces between unlike components of the solution, as in the
present system.
References
[
[
1] B.B. Kudrivavtsev, Sov. Phys. Acoust. 2 (1956) 36.
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1
[
[
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[
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0
0
.001125–0.009 molꢀ for polar solvents and 0.000515, 0.0045,
.009 molꢀ for non-polar solvents significant interaction between
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[
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Iodide +formamide+1,2-ethanediol mixtures at 298.15K, Ind. J. Pure Appl.
Phys. 35 (1997) 729.
solute and solvent is present (Fig. 10). The negative excess adia-
batic compressibility and excess intermolecular free length are
attributed to the presence of intermolecular interaction between
solute and solvent. This is especially true for solutions of concen-
tration 0.001125–0.0045 molꢀ for polar solvents and 0.000526–
[10] R.J. Fork, W.R. Moore, Trans. Faraday Sco. 61 (1965) 2105.
[
[
[
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0
.009 molꢀ. The rate of disruption of intermolecular interaction
[14] T. Sivaprasad, P. Venkateswarlu, Acoust. Lett. 18 (1) (1994).
[
15] V.A. Tabhane, O.P. Chimankar, S. Manja, T.K.J. Nambinarayanan, Pure Appl.
Ultrason. 21 (1999) 67–70.
between solvent molecules is increased as the polarity of the sol-
vent is increased. This results in an increase in the negative excess
volume and a decrease in the excess density of the solution
[
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[17] V.A. Tahbane, B.A. Patki, Acoustica 52 (1982) 44.
[
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Pramana 13 (1979) 105.
(Fig. 11). At a concentration of 0.018 molꢀ a maximum for excess
density is observed. This indicates that solvent–solvent interac-
tions are replaced by solvent–solute interactions. Thus, the positive
[
19] M.C.S. Srilalitha, C. Suliha, J. Rao, Pure Appl. Ultrason. 18 (1996) 59.
[20] S.L. Oswal, Desaih, Fluid Phase Equilibra 149 (1998) 359.
s f
excess velocity, acoustic impedance, and negative excess K and L