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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue IV, April 2026
Variation of Ultrasonc and Thermo Acoustic Parameters of CYNO
Byphenyl Liquid Crystal(8OCB) With Temperature
Dr. M. Baba Fakruddin, Dr. K. P. Venkateswara Rao
Sri Sai Baba National Degree College (Autonomous), Anantapuramu-515001, A. P
DOI: https://doi.org/10.51583/IJLTEMAS.2026.150400067
Received: 10 April 2026; Accepted: 15 April 2026; Published: 08 May 2026
ABSTRACT
This research paper communicates the investigations of variation of Ultrasonic and thermoacoustic parameters
with temperature of a technically important Liquid crystal 8OCB (4′-octyloxy-4-cyanobiphenyl). Parameters
like adiabatic compressibility, Molar sound velocity, Molar compressibility and intermolecular free length and
also certain thermoacoustic parameters like., isochoric temperature coefficient of internal pressure (χ), isochoric
temperature coefficient of volume expansivity (χ′), pressure co-efficient of bulk modulus (c₁), reduced
compressibility (β), reduced volume (v
) and Sharma constant (S₀) are also evaluated. The anomalous behaviour
observed in ultrasonic and thermoacoustic parameters provide supporting evidence to the smectic A- nematic
transitions at 66°C and nematic- isotropic transition at 78°C of the liquid crystal under study.
INTRODUCTION
8OCB is a thermotropic liquid crystal compound consisting of highly polar rod like molecules. It is a low molar
mass liquid crystal (LC), which shows different liquid crystalline phases depending on temperature conditions.
Under normal temperature conditions 8CB exists only as a bulk smectic-A phase.(1) Temperature variation of
Ultrasonic velocity was first used to examine phase transition by Gabrielli and Verdini (2) which was confirmed
by other workers (3,4). The ultrasonic parameters viz velocity, adiabatic compressibility, Molar sound velocity,
intermolecular free length etc., show anomalous behaviour at the phase transition temperature. In addition to this,
thermal microscopy (5,6) studies also used to study the phase transition of liquid crystals. But no attempt is made
to use the thermoacoustic parameters to confirm the phase transition of the liquid crystals except the few studied
by D.P.Singh et al (7). So in the present study an attempt is made to estimate various thermoacoustic parameters
including Sharma constant in the liquid crystal 8 OCB using only one parameter namely the co-efficient of
volume expansion (α).
Theory
The relations used to estimate the ultrasonic parameters like adiabatic compressibility (β_ad), molar sound
velocity (Rm), molar compressibility (B) and intermolecular free length (L
f
) are given in our earlier
communications (8,9). The theoretical procedure for the estimation of various thermo-acoustic parameters
employing only the co-efficient of volume expansion (α) is essentially the same as that was given by Sharma
and Reddy (10,11) and is followed without any modification only the relations are given below.
Harward and Parker (12) obtained an expression for the isochoric temperature coefficient of internal pressure
(χ) as
(1)
The reduced volume (
) and reduced compressibility (
) is obtained from α as
(2)
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and
(3)
The isochoric temperature co-efficient of volume expansivity (χ′) can be written as
(4)
Molewyn - Hughes (13,14), parameter (c1) is given as
(5)
The Sharma constant is given by
(6)
and Huggins (14) parameter (F) is related to
as
(7)
RESULTS AND DISCUSSION
The Ultrasonic, density data required in this investigation are taken from (15,16).
The ultrasonic parameters are presented in Table - 1, and the various thermoacoustic parameters of the liquid
crystal 8 OCB estimated in the entire temperature region by the authors are presented in Table 2.The thermal
microscopy studies (4) revealed that the liquid crystal 8 OCB has a smectic A - nematic transitions at a
temperature of 66°C and a nematic - isotropic transition at 78°C. From the Table -1, it can be observed that at
the temperature 339°K adiabatic compressibility has a low value and Molar sound velocity, Molar
compressibility has a maximum value. A similar behaviour is also observed at the temperature 351°K. This
confirms the smectic A - nematic transition at 339°K and nematic - isotropic transition at 351°K.(16)
From the observation of the Table - 2 it can be noticed that all the thermo acoustic parameters show pre
transitional effect at and in the immediate vicinity of transition temperature.
The Sharma constant S₀ which is a very important parameter throw some light in understanding the molecular
order and inter molecular interactions in the condensed phase. It can be seen that even in the liquid crystalline,
where the mesogen simultaneously exhibits anisotropic properties of crystal as well as the rheological properties
of liquids, the value of Sharma constant is also constant with the same characteristic constant value of 1.11 ±
0.01 as was reported by Sharma and Sharma and Reddy, in certain non-mesomorphic systems.
Only at and in the immediate vicinity of isotropic - nematic transition and smectic A - nematic transitions the
value S₀ changes to a lower value which is less than the characteristic value. Exactly at the transition temperature
it exhibits lower values which can be used to detect the exact transition.
In a similar way the other thermo acoustic parameters Isochoric temperature co-efficient of volume expansivity
(χ′), the isochoric temperature coefficient of internal pressure (χ), reduced compressibility (β), the reduced
volume (V
), the Huggins parameter (F), the parameters S* and S₀* also show anomalous behaviour and pre-
transitional effects.
Table 1: Variation of Ultrasonic Parameters with Temperature of Liquid Crystal 8 OCB
Temperature
T K
Ultrasonic
Velocity U
m/s
Specific
Volume
V cm
3
/g
Adiabatic
Compressibility
B
ad
×10
12
Molar
sound
Velocity
Molar Compressibility
B
Intermolecular free
length L
f
A
O
331
1600
0.9862
38.52
3546
9321
0.3916
333
1605
0.9871
38.31
3553
9337
0.3906
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335
1585
0.9855
39.35
3543
9314
0.3935
337
1575
0.9905
39.29
3542
9335
0.3955
339
1695
0.9921
34.53
3636
9524
0.3708
341
1623
0.9934
37.72
3589
9417
0.3875
343
1595
0.995
39.11
3574
9384
0.3946
345
1590
0.9975
39.46
3577
9395
0.3963
347
1588
0.998
39.56
3579
9396
0.3968
349
1586
1.0014
39.81
3590
9420
0.3981
351
1610
1.004
38.73
3617
9482
0.3926
353
1570
1.0066
40.96
3596
9435
0.4032
355
1550
1.0081
41.96
3986
9412
0.4087
Table 2 : Variation of Thermo-Acoustic Parameters of Liquid Crystal 8 OCB
Temperature
χ ×10⁴
c₁
V
B
χ
χ′
S₀
V
S₀*
S*
331
8.04
8.3634
1.229
5.610
0.5509
1.545
1.12
1.184
1.133
1.364
333
8.10
8.4004
1.228
5.614
0.5484
1.539
1.12
1.189
1.132
1.359
335
8.15
8.3600
1.230
5.644
0.5478
1.546
1.12
1.183
1.133
1.364
337
10.75
7.5767
1.290
6.885
0.5009
1.725
1.11
1.016
1.163
1.483
339
15.21
6.9602
1.380
9.410
0.4317
2.031
1.09
0.743
1.204
1.688
341
10.60
7.5818
1.289
6.854
0.5027
1.723
1.11
1.022
1.163
1.482
343
9.82
7.7513
1.274
6.534
0.5123
1.674
1.11
1.062
1.155
1.499
345
9.80
7.7418
1.275
6.559
0.5111
1.672
1.12
1.064
1.155
1.451
347
9.91
7.6998
1.278
6.611
0.5105
1.688
1.12
1.053
1.157
1.459
349
16.25
6.8528
1.407
10.381
0.4112
2.214
1.08
0.653
1.215
1.756
351
29.56
6.6805
1.601
23.197
0.2651
3.075
0.94
0.118
1.290
2.383
353
18.35
6.7408
1.447
12.069
0.3804
2.296
1.06
0.515
1.232
1.864
355
9.84
7.6618
1.281
6.668
0.5095
1.699
1.12
1.044
1.159
1.466
CONCLUSION
From the results, obtained in the present investigation we can conclude that, the thermo acoustic parameters can
also be used to study the phase transition in addition to the Ultrasonic parameters. The sharp change in these
values can be used to detect the exact phase transition temperature.
ACNOWLEDGEMENTS
The authors gratefully acknowledge the support and encouragement given by Sri.P.LN.Reddy, the Correspondent,
SSBN College, ANANATAPUR, A.P, India.
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