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Mahahpatra, Sabyasachi

Low-Lying States of 11Be and 15C

Sreelatha, C J

Satyanarayana, Ch

Anuradha, P

Indian J. Phys. 81 (8), 779-785 (2007) 
Excess refractive index studies on CSA-DMSO binary 
mixture showing lyophase 
C J Sreelatha, Ch Satyanarayana and P Anuradha* 
Department of Physics.Kakatiya University, Warangal-506 009, Andhra Pradesh, India 
E-mail anu_phys_ku(«>yahoo com 
Received 4 August 2006, accepted 1 August 2007 
Abstract Binary mixtures of ceto stearyl alcohol (CSA) and dimethyl sulfoxide (DMSO) are found to exhibit 
mesophase over wide range of concentrations The specific volume data, volume expansivity and refractive 
index variations are useful in the study of physico-chemical properties of materials. The clear measurement of 
transition temperature, from the isotropic liquid phase to anisotropic mesophase plays an important role in the 
above studies. The transition temperature studies, through refractive index variation with temperature for 
different concentrations, are presented in this paper. The excess refractive index variation as a function of 
temperature are also presented 
Keywords : Lyophase, optical anisotropy, excess refractive index, Walter's equation, birefringence 
PACS Nos. 61.3-v, 61 3 St, 42.70 Df, 78.20 Ci 
1. Introduction 
The term liquid crystal signifies a state of aggregation intermediate between a crystalline 
solid and an isotropic liquid phase. Lyotropics can be formed by binary mixtures, of 
which one component may be mesogenic. Mixed liquid crystals of two compounds which 
are also mesogenic [1]. Ceto stearyl alcohol (CSA) is a solid mixture consisting of stearyl 
alcohol and cetyl alcohol. It can be extracted from sperm oil, in which the alcohols occur, 
or by reduction of the mixture of stearic and palmitic acids of natural fats. Ceto stearyl 
alcohol may either contain 90% of stearyl alcohol and 10% of cetyl alcohol or 40% 
stearyl alcohol and 60% of cetyl alcohol. It is in the form of white or cream flakes. The 
compound supplied by M/s Loba Chemie Pvt. Ltd., Bombay, was used after recrystallization 
in benzene solution. It showed a melting point of 53°C (±0.5°C) as observed under polarizing 
Corresponding Author 
©2007IACS 
780 C J Sreelatha, Ch Satyanarayana and P Anuradha 
microscope. The composition of CSA used by us was determined to be 40% stearyl 
alcohol and 60% cetyl alcohol using Walter's equation 
Tm-m^-t2C2)/(C^C2) (1) 
for the melting point of the binary mixtures of isomorphous substances. The melting point 
of cetyl alcohol and stearyl alcohol were taken as 50°C and «58°C respectively [2]. 
Ceto stearyl alcohol extracted from appropriate acids from sperm oil in the ratio 60 : 
40 exhibits lyotropic mesomorphism in the pure state [3]. In this study the mesomorphism 
exhibited by the binary mixtures of CSA and dimethyl sulfoxide (DMSO) mixed in different 
concentrations is studied over a range of temperatures. 
The uniaxial symmetry around the molecular axis or the director (in a nematic phase) 
leads to anisotropy is many physical properties such as refractive index, dielectric 
permittivity, magnetic susceptibility etc. These parameters have different values parallel to 
and at right angles to the molecular axis. In order to measure these quantities, samples 
with well-defined molecular orientation pattern is necessary. Two limiting cases arise in 
view of the above criteria : (i) homeotropic layers, in which the director or the molecular 
axis is every where perpendicular to the walls of sample holder, and (ii) a uniform planar 
layer in which the director or the molecular axis is parallel to one direction in the plane of 
the substrate [4,5]. Thus surface preparation of a substrate to get oriented sample is an 
important process. Excellent reviews furnishing information about the surface produced 
alignment of the samples are available in the literature [6-9]. 
2. Experimental 
Using polarizing microscope attached with hot stage, the transition temperature from 
isotropic liquid phase to lyotropic phase for concentrations ranging from 20% to 95% of 
ceto stearyl alcohol in dimethyl sulfoxide are studied. The solution of ceto stearyl alcohol 
in dimethyl sulfoxide at a temperature about 60°C (where it is isotropic solution) is taken 
over a microscope glass slide and covered by a coverslip. The samples are observed 
under polarizing microscope with crossed polaroids. When the sample is allowed to cool 
slowly at the transition temperature, textures typical to the lyotropic lamellar mesophase 
have been observed in the binary mixtures of CSA in DMSO. The following textures have 
been identified from photo-micrographs, (i) The batonnets typical of lamellar phase for the 
concentration of 22% CSA in DMSO, (ii) small droplets with pin wheeled crosses and 
circular discs for the same concentration, (iii) oil streaks and tubes from the concentration 
of 42% CSA in DMSO, (iv) isotropic polyhedral textures for concentration 53% of CSA in 
DMSO, (v) focal conic textures for the concentration of 85% CSA in DMSO. Similar 
textures are also seen in samples of concentration range 90%, 95% of CSA in DMSO. 
Phase diagram of binary mixtures of CSA and DMSO is shown in Figure 1. 
The temperature variation of the refractive indices of the samples were measured to an 
accuracy of ±0.0005. Temperatures were measured with an accuracy of ±0.1 °C using 
Excess refractive index studies on CSA-DMSO binary mixture etc 781 
Abbe refractometer (Toshniwal Instruments and Engineering Company, New Delhi). The 
principle involved in the measurement of refractive index using this refractometer is the 
critical angle. A few drops of the sample to be studied are placed between the illuminated 
60 
50 
40 
| 30 
120 
10 
0 
0 20 40 60 80 100 120 
Concentration of CSA (by vrt%) in DMSO 
Figure 1. Phase diagram of binary mixture of CSA and DMSO; (i) below transition temperature : anisotropic 
mesophase (lyotropic phase), (ii) above transition temperature : isotropic liquid phase. 
prisms which is maintained at the desired temperature by water circulation arrangement 
around the prism [10]. The lower prism of the Abbe refractometer is rubbed using fine 
cotton along the transverse direction of the prism gently several times till it is ensured 
that the oriented sample is deposited. The sample is taken in the liquid state at the 
higher temperature and is embedded between the two prisms. By slowly lowering the 
temperature the refractive index is directly measured at different temperatures. 
The refractive indices along the direction of the molecular orientation and in the direction 
perpendicular to the molecules are identified by the known vibration directions of an external 
analyzer used along with the refractometer following the procedure adopted by 
Madhusudhana et al [11] and Somashekar et al [12]. The refractive index measured with 
the vibration direction parallel to the molecular axis (optic axis) of the oriented sample is 
denoted by ne and the vibration direction rotated perpendicular to the direction of molecular 
axis is denoted by n0. From these values the mean refractive index is calculated for the 
mixtures of CSA and DMSO using the relation 
("e + 2n0). (2) 
2.1. Optical parameters-excess refractive index: 
Thermodynamic properties of mixed systems and the binary mixtures in particular containing 
self-associated components, exhibit deviations from ideal behavior that arise not only due 
to difference in molecular size and shape but also due to the hydrogen bonding between 
' ' a u o • " 
782 CJSreelatha, Ch Satyanarayana and P Anuradha 
like and unlike molecules. The various physical properties of such mixtures depend on 
the degree of association in the pure state, the structure breaking ability of the components 
and the interaction due to hydrogen bonding between like and unlike molecules of the 
constituents [13-16]. Number of mixtures such as butyl amine, propanol, aliphatic alcohol, 
some alkanes in proper solvents have been studied as regards to their ultrasound velocities, 
specific volume, dielectric constant etc., varying concentrations at different temperatures 
[17-20]. Densities, viscosities, dielectric constants and IR spectral studies of acetonitrile-
toluene system with varying concentration and at different temperatures have been measured 
experimentally. These properties have been fitted to a polynomial equation [17,19]. The 
experimental results and excess parameters have also been calculated using the relation 
of the type 
ME = Mem-(C,m,+C2m2) (3) 
where MF is the excess parameter of the physical property, /Wexpt is the experimentally 
measured physical property, m1 and m2 the physical property of first and second 
components and C, and C2 the concentration of two components. 
Eq. (3) may be extended to any compound system while studying excess parameter. 
The binary mixtures of CSA and DMSO with varying concentrations have been taken and 
their refractive indices over a temperature range sufficiently above and below the transition 
temperature have been experimentally studied. The mean refractive index (n^pt) of e a c h 
sample as a function of temperature is calculated using eq. (2). These values of n^ 
are shown in Table 1 and represent the experimetnal values. Following the additive rule 
with the knowledge of concentrations (Cv C2) of constituents in each mixture, the theoretical 
value of the refractive index as a function of temperature is calculated. Substituting the 
experimental value and the calculated value of the refractive index in eq. (3), the excess 
refractive index (n£) is calculated for each sample as a function of temperature and is 
also shown in Table 1. 
3. Results and discussion 
The excess refractive index plotted as a function of temperature shown in Figure 2 reveals 
that the excess parameter goes on decreasing with increasing temperature upto transition 
temperature. Then it changes sign and goes to negative minimum with further increase of 
temperature. This trend is observed in mixtures up to 89% by weight of CSA. At higher 
concentration above 90% by weight of CSA the excess refractive index remains negative 
but trend variation is the same as observed in the case of mixtures with lower concentration. 
The change of excess refractive index with concentration and temperature is in accordance 
with the predictions reported earlier in the case of other organic compound mixtures 
[13-20]. 
Table 1. Excess refractive indices versus temperature of mixtures of CSA and DMSO. 
Cone, of 
CSAWt% 34 36 38 40 
100 /££, 1.4912 1.4915 1.4893 1.4882 
0 " £ £ 1.455 1.454 1.453 1.4525 
42 r Q 1.4735 1.4708 1.463 1.444 
rf 0.0033 0.0006 -0.0072 -0.0262 
53 n™t 1.4872 1.4867 1.485 1.4833 
rf 0.0130 0.0125 0.0118 0.0091 
58 n|£, 1.4833 1.4823 1.4817 1.4797 
rf 0.0073 0.0063 0.0057 0.0037 
72 n™x 1.4853 1.4843 1.4833 1.4817 
rf 0.0039 0.0029 0.0019 -0.0009 
78 /•££, 1.4853 1.4848 1.4838 1.4823 
rf 0.0021 0.0016 0.0006 -0.0009 
95 nj£ t 1.488 1.4877 1.4865 1.4852 
rf -0.0014 -0.0017 -0.0029 -0.0042 
42 44 46 48 50 
1.4865 1.485 1.4835 1.4815 1.4795 
1.4515 1.4505 1.4495 1.449 1.448 
1.4435 1.4425 1.442 1.441 1.44 
-0.0277 -0.0277 -0.0282 -0.0292 -0.0302 
1.48 1.481 1.478 1.437 1.435 
0.0058 0.0068 0.0038 -0.0372 -0.0392 
1.4772 1.442 1.4385 1.4375 1.436 
0.0012 -0.0340 -0.0375 -0.0335 -0.0400 
1.4803 1.4787 1.4767 1.441 1.4365 
-0.0011 -0.0027 -0.0047 -0.0404 -0.0449 
1.4800 1.4777 1.472 1.437 1.435 
-0.32 -0.0055 -0.0112 -0.0462 -0.0482 
1.4842 1.4825 1.4807 1.4782 1.4370 
-0.0052 -0.0069 -0.0087 -0.0112 -O.0524 
52 54 56 58 60 
1.4772 1.431 1.4295 1.4285 1.427 
1.447 1.445 1.446 1.4445 1.444 
1.439 1.438 1.4375 1.436 1.435 
-0.0312 -0.0322 -0.0327 -0.0342 -0.0352 
1.435 1.4335 1.433 1.432 1.432 
-0.0392 -O.0407 -0.0412 -0.0422 -0.0422 
1.4345 1.4335 1.4325 1.431 1.4305 
-0.0415 -0.0425 -0.0435 -0.0450 -0.0455 
1.434 1.431 1.4305 1.429 1.428 
-0.0474 -0.504 -0.0509 -0.0524 -0.0534 
1.435 1.434 1.4325 1.432 1.4315 
-0.0482 -0.0492 -0 0507 -0 0512 -0.0517 
1.4345 1.4315 1.4290 1.4270 1.4260 
-0.0549 -0.0579 -0.0604 -0.0624 -0.0634 
784 CJSreelatha, Ch Satyanarayana and P Anuradha 
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F i g u r e 2 . Temperature versus excess refractive index for different concentration of C S A . 
Acknowledgments 
We thank Prof. K G Subhadra, Dr. A S Nageshwara Rao and Dr. C Radhakrishna Murthy 
for their keen interest and for helpful discussions. 
Excess refractive index studies on CSA-DMSO binary mixture etc 785 
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[3] Martindale, Extrapharmacopicia (29th ed) (Pharmacentical Press) ed James E E Reynolds (1989) 
[4] G Fnedel Les etats mesomorphous de la matiere Ann de Physique 18 273 (1922) 
[5] W H De Jeu Physical Properties of liquid crystalline materials (New York Gordon Breach) 
(1979) 
[6] H Kelker and R Hatz Hand Book of Liquid Crystal (Weinheim Verlag, Chemie) (1979) 
[7] D Demus and L Richter Textures of liquid crystals (VEB, Verlag Leipzig) (1978) 
[8] E Guyon and W Urbach in Non emissive electropic displays (eds) A R Kmetz and F K Von 
Wilhsen (New York Plenum) (1976) 
[9] F J Kahn, G N Taylor and H Schonhorn Proc IEEE 61 823 (1973) 
[10] Robert Hicks et al Laboratory Instrumentation (llnd ed) (Harper and Row) 
[11] N V Madhusudana, R Shashtdhar and S Chandrasekhar Mol Cryst Liquid Cryst 13 61 (1971) 
[12] R Somashekar, D Revannasiddaiah, M S Madhava, H S Subramanyam and Krishna Murti Mol Cryst 
Liquid Cryst 45 243 (1978) 
[13] J R Taylor, S L Arura and J L Fergason Phys Rev Lett 24 359 (1970) 
[14] A De vnes Acta Crystallogr A25 135 (1969) 
[15] J C Schug and E Chang J Phys Chem 75 938 (1971) 
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[17] A M Levelut and M C Lambert R hebd stance Acad Set Pans 272B 1018 (1971) 
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[20] A Knshnaiah, D N Rao and P R Naidu J Pure Appl Phys 19 1113 (1981) 


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Excess Refractive Index Studies on CSA-DMSO Binary Mixture Showing Lyophase

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Low-Lying States of <SUP>11</SUP>Be and <SUP>15</SUP>C

Excess Refractive Index Studies on CSA-DMSO Binary Mixture Showing Lyophase

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