- Email: [email protected]
Liquid crystalline behaviour of N-cetyl N,N,N,-trimethyl ammonium bromide: An experimental study
Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98 www.elsevier.com/locate/pcrysgrow
Liquid crystalline behaviour of N-cetyl N,N,N,-trimethyl ammonium bromide: An experimental study M.K. Dwivedi a, R.A. Yadav b, S.N. Tiwari a,* a
Department of Physics, DDU Gorakhpur University, Gorakhpur 273 009, India b U.P. Jal Nigam, Rana Pratap Marg, Lucknow 226 001, India
Abstract Ultrasonic velocity, dielectric constant, specific conductance, viscosity, density and other related physical properties of a lyotropic liquid crystal namely N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) in aqueous solution at various compositions have been studied. Solutions of different concentrations of CTAB in NaCl have been prepared. The change in miceller aggregation of the liquid crystal is indicated by the variation in the physical parameters within a range of concentration. Results have been used to elucidate the liquid crystalline behaviour of the compound in the solution. Ó 2006 Elsevier Ltd. All rights reserved. PACS: 43.35.Bf; 61.30.-v; 61.30.Eb; 61.30.Gd; 61.30.St; 64.43.Bn; 64.70.Md Keywords: A1. Diffusion; A1. Fluid flows; B1. Polymers; B2. Dielectric materials (Liquid crystals/Nematogens)
1. Introduction In the mixture of certain compounds (like soaps, sodium or potassium salts of higher fatty acids, deoxyribonucleic acid, synthetic polypeptides, lecithin and cholesterol, etc.) with controlled amount of water (or other polar solvents), the special property of solute molecules leads to the formation of clusters and sometimes cluster of the clusters in a variety of interesting * Corresponding author. Tel.: þ91 551 2203182; fax: þ91 551 2340459. E-mail address: [email protected] (S.N. Tiwari). 0960-8974/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.pcrysgrow.2006.03.013
92
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
geometrical shapes. Some of these aggregates are liquid crystals, known as lyotropic which are quite different from thermotropic liquid crystals. Lyotropic liquid crystals composed of two component systems viz. water and amphiphilic compounds, have a polar head (ionic) which tends to dissolve in water (hydrophilic) and an organic tail (hydrophobic) which is not soluble in water [1]. Addition of water to the crystalline form of an amphiphile disrupts the ordered crystal lattice in stages and a series of structures can be generated. Classically, the aggregates can be infinite with flat or cylindrical interfacial curvatures, and packed with long range translational order in the well known lamellar, cubic and hexagonal phases; or they can be finite, quasi-spherical and packed without any long range order in the micellar phase. It has been shown that long range ordering of finite aggregates is possible. In translational order, micelles build a cubic structure while in orientational order, oblate or prolate spheroids are dispersed in the solution with their axes nearly parallel to each other and a nematic phase is formed [2e4]. Lyotropic amphiphilic nematic phases were first found to exist in the quaternary system of sodium dodecylsulphate, sodium sulphate, decanol and D2O. Quaternary systems have generally been found to be very flexible, frequently stable when subjected to large variations in composition and temperature. Detergents such as potassium dodecanoate, alkyl trimethylammonium bromides and decylammonium chloride provide quaternary nematic mesophases [5e8]. Nematic phase samples can also be obtained by using mixed detergents with oppositely charged head groups. Most quaternary systems can be modified by leaving out the salt resulting in ternary systems which still maintain a nematic phase under a wide range of temperatures and composition variations [9]. The ideal lyotropic amphiphilic nematic phase systems from the theoretical and experimental point of view can be derived from a binary system of detergent and D2O only. Awell defined phase diagram of cesium perfluorooctanoate (CsPFO)/D2O has been demonstrated where the lamellar phase undergoes a phase transition to the isotropic phase by two processes (i) directly via a first order transition and (ii) indirectly via a second order transition through a nematic phase [10]. The present paper deals with the structural analysis based on physical parameters like ultrasonic velocity, density, dielectric constant, specific conductance carried out in the case of Ncetyl N,N,N-trimethyl ammonium bromide/water system at various compositions. To see the effect of additives on the physical properties of the binary system, 0.05 N NaCl, 0.1 N NaCl and 0.5 N NaCl solutions have been used and results have been discussed to elucidate the liquid crystalline behaviour of CTAB in the light of existing theories [10e15]. 2. Experimental method Material under investigation (CTAB) has been procured from M/S Loba Chemie, India and fresh double distilled water has been used. Ultrasonic velocity measurements have been carried out using a single crystal variable path interferometer obtained from M/S Mittal Enterprises, New Delhi. All observations have been carried out at room temperature i.e. 29 C. The determination of ultrasonic velocity has unique advantage in evaluating some important physical parameters such as adiabatic compressibility, isothermal compressibility, specific heat at constant volume and ratio of specific heats, etc. The details of experimental procedure may be found in literature [16e18]. 3. Results and discussion In general, translation in micellar solutions as a function of concentration takes place. The micelles are spherical at low concentrations and become rods at higher concentrations. This is
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
93
H2O
1532
0.05N NaCl 0.1N NaCl 0.5N NaCl
Ultrasonic Velocity (m/s)
1528
1524
1520
1516
1512
1508
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 1. Concentration dependence of ultrasonic velocity of CTAB molecule in different solvents.
reflected by the behaviour of CTAB/water system at 29 C. The change in the micellar form is indicated by the variation of the physical parameters (Figs. 1e9) within a range of concentrations whose limits are approximately determined. The concentrations at which the onset of this transformation takes place depend on the amphiphile and temperature but do not seem to be simply related to the thickness of the water layer separating neighbouring micelles since it varies greatly from one amphiphile to another. Fig. 1 shows discontinuous change in the ultrasonic velocity corresponding to the critical micellar concentration value and continuous changes corresponding to the spherical rod-like
1.4
H2O 0.05N NaCl 0.1N NaCl 0.5N NaCl
Dielectric Constant (arbitrary unit)
1.35 1.3 1.25 1.2 1.15 1.1 1.05 1 0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 2. Concentration dependence of dielectric constant of CTAB molecule in different solvents.
94
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98 4.5 H2O 0.05N NaCl
Specific Conductance (ohm/cm)
4
0.1N NaCl 0.5N NaCl
3.5 3 2.5 2 1.5 1 0.5 0 0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 3. Concentration dependence of specific conductance of CTAB molecule in different solvents.
micelles and rod-like middle phase transitions. Separation into two phases, the micellar solution and the liquid crystalline middle phase, is observed at higher concentration (¼25%) where change in ultrasonic velocity is marked. As the concentration of NaCl in CTAB water solution is increased, critical micellar concentration (c.m.c.) value and concentration corresponding to other transitions shift to higher values and less sharp changes in the ultrasonic velocity are observed, which ultimately vanish at higher concentration of NaCl. Changes in the c.m.c. i.e., the maximum concentration of molecular dispersion are a measure of the balance of forces causing the formation of micelles.
0.7
H2O 0.05N NaCl
Specific Viscosity (arbitrary unit)
0.6
0.1N NaCl 0.5N NaCl
0.5 0.4
0.3 0.2 0.1 0
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 4. Concentration dependence of specific viscosity of CTAB molecule in different solvents.
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98 1.033
95
H2O 0.05N NaCl 0.1N NaCl
1.028
0.5N NaCl
Density (g/c.c.)
1.023
1.018
1.013
1.008
1.003
0.998
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 5. Concentration dependence of density of CTAB molecule in different solvents.
Dielectric behaviour (Fig. 2) reflects the relationship of permanent dipoles and molecular polarizability in the respective phases. From the experimental data in various phases, it may be observed that fast reorientation of the dipole moment around the long molecular axis and hindered reorientation around the short molecular axis exist. These two rotational possibilities are typical for liquid crystals and contrary to the phase where these movements are frozen. Specific conductance (Fig. 3), specific viscosity (Fig. 4) and density (Fig. 5) values have been found to show continuous change corresponding to various transformations. Transformations corresponding to different concentrations of CTAB/water system become insignificant at higher
Adiabatic Compressibility (1012 cm2/dyne)
44
43.8
43.6
43.4
43.2
43
42.8
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 6. Concentration dependence of adiabatic compressibility of CTAB in H2O as a solvent.
96
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
Molar Compressibility [cm3(dyne/cm2)1/7]
213
212.5 212
211.5 211
210.5 210
209.5
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 7. Concentration dependence of molar compressibility of CTAB molecule in H2O as a solvent.
NaCl concentration (¼0.5 N NaCl), where NaCl prevents the formation of suitable micelles in the above mentioned concentration range. Change in the concentration corresponding to phase transitions shifts towards higher values on addition of NaCl. This is due to the increased hydration of the ethylene chain caused by a reduction in the cooperative structure of water. Physical parameters such as adiabatic compressibility (Fig. 6), molar compressibility (Fig. 7), molar sound velocity (Fig. 8), and intermolecular free length (Fig. 9) derived from the experimental data show anomalous behaviour corresponding to the different transitions occurring at various concentrations. Since the above parameters are derived from ultrasonic velocity and density data, similar changes are expected to occur on addition of NaCl. Similar to the observed in case of thermotropic liquid crystal mixtures, anomalous behaviour observed in the lyotropic system decreases as the concentration of NaCl in CTAB/water system 4180
Molar Sound Velocity
4172 4164 4156 4148 4140 4132 4124
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 8. Concentration dependence of molar sound velocity of CTAB molecule in H2O as a solvent.
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
97
0.419
Intermolecular Freelength (A.U.)
0.418
0.417
0.416
0.415
0.414
0.413
0.412 0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 9. Concentration dependence of intermolecular freelength of CTAB molecule in H2O as a solvent.
is increased. These experiments suggest that the building units of the phase are not necessarily inherently isotropic and therefore, it may be inferred that spherical micelles do not form the middle phase. 4. Conclusion N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) forms liquid crystalline region in the range of certain concentrations. Changes in the various physical properties reflect the transformations occurring at different transitions in a remarkable manner. The magnitude of these changes decreases on addition of electrolytic solution of different potency and vanishes completely at very high concentration of the electrolytic solution.
Acknowledgement MKD is thankful to UGC, New Delhi for awarding Junior Research Fellowship.
References [1] P.J. Wojtowicz, in: E.B. Priestley, P.J. Wojtowicz, P. Sheng (Eds.), Introduction to Liquid Crystals, Plenum Press, New York, 1974. [2] C.L. Khetrapal, A.C. Kumar, A.S. Tracey, P. Diehl, in: P. Diel, E. Fluck, R. Kosfeld (Eds.), NMR Basic Principle and Progress, vol. 9, Springer-Verlag, Berlin, 1975. [3] P.S. Pershan, Phys Today 35 (1982) 34.
98
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
[4] J. Charvolin, Mol. Cryst. Liq. Cryst. 113 (1984) 1. [5] A. Saupe, Nuovo Cimento D Ser. 1 (1984) 16. [6] P.A. Winsor, in: G.H. Brown, M.M. Labes (Eds.), Liquid Crystals 3, Part I, vol. 43, Gordon and Breach, New York, 1972. [7] L.W. Reeves, A.S. Tracey, M.M. Tracey, J. Am. Chem. Soc. 9 (1973) 3799. [8] N. Boden, H.C. Holmes, Chem. Phys. Lett. 109 (1984) 76. [9] K. Radley, A.S. Tracey, Mol. Cryst. Liq. Cryst. Lett. 95 (1985) 1. [10] N. Boden, S.A. Corne, K.W. Jolley, Chem. Phys. Lett. 105 (1984) 99. [11] A.J.F. Bombard, I. Joekes, M.R. Alcantara, M. Knobel, Mater. Sci. Forum 416 (2003) 753. [12] M.R. Alcantara, E.G. Fernandes, Mol. Cryst. Liq. Cryst. 378 (2002) 89; 383 (2002) 37. [13] A.J.F. Bombard, I. Joekes, M.R. Alcantara, M. Knobel, J. Intel. Mater. Syst. Struct. 13 (2002) 471. [14] M.R. Alcantara, A.F. Moura, E.G. Fernandes, Liq. Cryst. 29 (2002) 191. [15] M.R. Alcantara, A.F. Moura, E.G. Fernandes, Mol. Cryst. Liq. Cryst. 333 (1999) 69. [16] N.K. Sanyal, R.A. Yadav, S.R. Shukla, Acoustica 59 (1986) 233. [17] N.K. Sanyal, R.A. Yadav, S.R. Shukla, Phys. Status Solidi A 99 (1987) 551. [18] S.N. Tiwari, R.A. Yadav, S.R. Shukla, N.K. Sanyal, in: B.K. Agrawal, H. Prakash (Eds.), Condensed Matter Physics, Narosa Publishing House, New Delhi, 1999, p. 182. Mr. M.K. Dwivedi is a Ph.D. student.
Dr. R.A. Yadav obtained his Ph.D. degree from Gorakhpur University, Gorakhpur and is presently working as Geophysicist. He has published more than fifteen research papers. His field of interest is liquid crystals.
Dr. S.N. Tiwari (Sugriva Nath Tiwari) obtained his M.Sc. and Ph.D. degrees in Physics from D.D.U. Gorakhpur University, Gorakhpur and is presently working as Reader in the Department of Physics, D.D.U. Gorakhpur University, Gorakhpur, India. He has been conferred ISCA Young Scientist Award in 1988. His research areas of interest are Material Science (Liquid Crystals), Molecular Biophysics, Biosensors and Radiation Biophysics. Dr. Tiwari has successfully completed two research projects and has published more than forty research papers in various national and international journals.
Liquid crystalline behaviour of N-cetyl N,N,N,-trimethyl ammonium bromide: An experimental study M.K. Dwivedi a, R.A. Yadav b, S.N. Tiwari a,* a
Department of Physics, DDU Gorakhpur University, Gorakhpur 273 009, India b U.P. Jal Nigam, Rana Pratap Marg, Lucknow 226 001, India
Abstract Ultrasonic velocity, dielectric constant, specific conductance, viscosity, density and other related physical properties of a lyotropic liquid crystal namely N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) in aqueous solution at various compositions have been studied. Solutions of different concentrations of CTAB in NaCl have been prepared. The change in miceller aggregation of the liquid crystal is indicated by the variation in the physical parameters within a range of concentration. Results have been used to elucidate the liquid crystalline behaviour of the compound in the solution. Ó 2006 Elsevier Ltd. All rights reserved. PACS: 43.35.Bf; 61.30.-v; 61.30.Eb; 61.30.Gd; 61.30.St; 64.43.Bn; 64.70.Md Keywords: A1. Diffusion; A1. Fluid flows; B1. Polymers; B2. Dielectric materials (Liquid crystals/Nematogens)
1. Introduction In the mixture of certain compounds (like soaps, sodium or potassium salts of higher fatty acids, deoxyribonucleic acid, synthetic polypeptides, lecithin and cholesterol, etc.) with controlled amount of water (or other polar solvents), the special property of solute molecules leads to the formation of clusters and sometimes cluster of the clusters in a variety of interesting * Corresponding author. Tel.: þ91 551 2203182; fax: þ91 551 2340459. E-mail address: [email protected] (S.N. Tiwari). 0960-8974/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.pcrysgrow.2006.03.013
92
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
geometrical shapes. Some of these aggregates are liquid crystals, known as lyotropic which are quite different from thermotropic liquid crystals. Lyotropic liquid crystals composed of two component systems viz. water and amphiphilic compounds, have a polar head (ionic) which tends to dissolve in water (hydrophilic) and an organic tail (hydrophobic) which is not soluble in water [1]. Addition of water to the crystalline form of an amphiphile disrupts the ordered crystal lattice in stages and a series of structures can be generated. Classically, the aggregates can be infinite with flat or cylindrical interfacial curvatures, and packed with long range translational order in the well known lamellar, cubic and hexagonal phases; or they can be finite, quasi-spherical and packed without any long range order in the micellar phase. It has been shown that long range ordering of finite aggregates is possible. In translational order, micelles build a cubic structure while in orientational order, oblate or prolate spheroids are dispersed in the solution with their axes nearly parallel to each other and a nematic phase is formed [2e4]. Lyotropic amphiphilic nematic phases were first found to exist in the quaternary system of sodium dodecylsulphate, sodium sulphate, decanol and D2O. Quaternary systems have generally been found to be very flexible, frequently stable when subjected to large variations in composition and temperature. Detergents such as potassium dodecanoate, alkyl trimethylammonium bromides and decylammonium chloride provide quaternary nematic mesophases [5e8]. Nematic phase samples can also be obtained by using mixed detergents with oppositely charged head groups. Most quaternary systems can be modified by leaving out the salt resulting in ternary systems which still maintain a nematic phase under a wide range of temperatures and composition variations [9]. The ideal lyotropic amphiphilic nematic phase systems from the theoretical and experimental point of view can be derived from a binary system of detergent and D2O only. Awell defined phase diagram of cesium perfluorooctanoate (CsPFO)/D2O has been demonstrated where the lamellar phase undergoes a phase transition to the isotropic phase by two processes (i) directly via a first order transition and (ii) indirectly via a second order transition through a nematic phase [10]. The present paper deals with the structural analysis based on physical parameters like ultrasonic velocity, density, dielectric constant, specific conductance carried out in the case of Ncetyl N,N,N-trimethyl ammonium bromide/water system at various compositions. To see the effect of additives on the physical properties of the binary system, 0.05 N NaCl, 0.1 N NaCl and 0.5 N NaCl solutions have been used and results have been discussed to elucidate the liquid crystalline behaviour of CTAB in the light of existing theories [10e15]. 2. Experimental method Material under investigation (CTAB) has been procured from M/S Loba Chemie, India and fresh double distilled water has been used. Ultrasonic velocity measurements have been carried out using a single crystal variable path interferometer obtained from M/S Mittal Enterprises, New Delhi. All observations have been carried out at room temperature i.e. 29 C. The determination of ultrasonic velocity has unique advantage in evaluating some important physical parameters such as adiabatic compressibility, isothermal compressibility, specific heat at constant volume and ratio of specific heats, etc. The details of experimental procedure may be found in literature [16e18]. 3. Results and discussion In general, translation in micellar solutions as a function of concentration takes place. The micelles are spherical at low concentrations and become rods at higher concentrations. This is
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
93
H2O
1532
0.05N NaCl 0.1N NaCl 0.5N NaCl
Ultrasonic Velocity (m/s)
1528
1524
1520
1516
1512
1508
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 1. Concentration dependence of ultrasonic velocity of CTAB molecule in different solvents.
reflected by the behaviour of CTAB/water system at 29 C. The change in the micellar form is indicated by the variation of the physical parameters (Figs. 1e9) within a range of concentrations whose limits are approximately determined. The concentrations at which the onset of this transformation takes place depend on the amphiphile and temperature but do not seem to be simply related to the thickness of the water layer separating neighbouring micelles since it varies greatly from one amphiphile to another. Fig. 1 shows discontinuous change in the ultrasonic velocity corresponding to the critical micellar concentration value and continuous changes corresponding to the spherical rod-like
1.4
H2O 0.05N NaCl 0.1N NaCl 0.5N NaCl
Dielectric Constant (arbitrary unit)
1.35 1.3 1.25 1.2 1.15 1.1 1.05 1 0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 2. Concentration dependence of dielectric constant of CTAB molecule in different solvents.
94
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98 4.5 H2O 0.05N NaCl
Specific Conductance (ohm/cm)
4
0.1N NaCl 0.5N NaCl
3.5 3 2.5 2 1.5 1 0.5 0 0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 3. Concentration dependence of specific conductance of CTAB molecule in different solvents.
micelles and rod-like middle phase transitions. Separation into two phases, the micellar solution and the liquid crystalline middle phase, is observed at higher concentration (¼25%) where change in ultrasonic velocity is marked. As the concentration of NaCl in CTAB water solution is increased, critical micellar concentration (c.m.c.) value and concentration corresponding to other transitions shift to higher values and less sharp changes in the ultrasonic velocity are observed, which ultimately vanish at higher concentration of NaCl. Changes in the c.m.c. i.e., the maximum concentration of molecular dispersion are a measure of the balance of forces causing the formation of micelles.
0.7
H2O 0.05N NaCl
Specific Viscosity (arbitrary unit)
0.6
0.1N NaCl 0.5N NaCl
0.5 0.4
0.3 0.2 0.1 0
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 4. Concentration dependence of specific viscosity of CTAB molecule in different solvents.
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98 1.033
95
H2O 0.05N NaCl 0.1N NaCl
1.028
0.5N NaCl
Density (g/c.c.)
1.023
1.018
1.013
1.008
1.003
0.998
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 5. Concentration dependence of density of CTAB molecule in different solvents.
Dielectric behaviour (Fig. 2) reflects the relationship of permanent dipoles and molecular polarizability in the respective phases. From the experimental data in various phases, it may be observed that fast reorientation of the dipole moment around the long molecular axis and hindered reorientation around the short molecular axis exist. These two rotational possibilities are typical for liquid crystals and contrary to the phase where these movements are frozen. Specific conductance (Fig. 3), specific viscosity (Fig. 4) and density (Fig. 5) values have been found to show continuous change corresponding to various transformations. Transformations corresponding to different concentrations of CTAB/water system become insignificant at higher
Adiabatic Compressibility (1012 cm2/dyne)
44
43.8
43.6
43.4
43.2
43
42.8
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 6. Concentration dependence of adiabatic compressibility of CTAB in H2O as a solvent.
96
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
Molar Compressibility [cm3(dyne/cm2)1/7]
213
212.5 212
211.5 211
210.5 210
209.5
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 7. Concentration dependence of molar compressibility of CTAB molecule in H2O as a solvent.
NaCl concentration (¼0.5 N NaCl), where NaCl prevents the formation of suitable micelles in the above mentioned concentration range. Change in the concentration corresponding to phase transitions shifts towards higher values on addition of NaCl. This is due to the increased hydration of the ethylene chain caused by a reduction in the cooperative structure of water. Physical parameters such as adiabatic compressibility (Fig. 6), molar compressibility (Fig. 7), molar sound velocity (Fig. 8), and intermolecular free length (Fig. 9) derived from the experimental data show anomalous behaviour corresponding to the different transitions occurring at various concentrations. Since the above parameters are derived from ultrasonic velocity and density data, similar changes are expected to occur on addition of NaCl. Similar to the observed in case of thermotropic liquid crystal mixtures, anomalous behaviour observed in the lyotropic system decreases as the concentration of NaCl in CTAB/water system 4180
Molar Sound Velocity
4172 4164 4156 4148 4140 4132 4124
0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 8. Concentration dependence of molar sound velocity of CTAB molecule in H2O as a solvent.
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
97
0.419
Intermolecular Freelength (A.U.)
0.418
0.417
0.416
0.415
0.414
0.413
0.412 0
4
8
12
16
20
24
28
Concentration (g/100ml) Fig. 9. Concentration dependence of intermolecular freelength of CTAB molecule in H2O as a solvent.
is increased. These experiments suggest that the building units of the phase are not necessarily inherently isotropic and therefore, it may be inferred that spherical micelles do not form the middle phase. 4. Conclusion N-cetyl N,N,N-trimethyl ammonium bromide (CTAB) forms liquid crystalline region in the range of certain concentrations. Changes in the various physical properties reflect the transformations occurring at different transitions in a remarkable manner. The magnitude of these changes decreases on addition of electrolytic solution of different potency and vanishes completely at very high concentration of the electrolytic solution.
Acknowledgement MKD is thankful to UGC, New Delhi for awarding Junior Research Fellowship.
References [1] P.J. Wojtowicz, in: E.B. Priestley, P.J. Wojtowicz, P. Sheng (Eds.), Introduction to Liquid Crystals, Plenum Press, New York, 1974. [2] C.L. Khetrapal, A.C. Kumar, A.S. Tracey, P. Diehl, in: P. Diel, E. Fluck, R. Kosfeld (Eds.), NMR Basic Principle and Progress, vol. 9, Springer-Verlag, Berlin, 1975. [3] P.S. Pershan, Phys Today 35 (1982) 34.
98
M.K. Dwivedi et al. / Progress in Crystal Growth and Characterization of Materials 52 (2006) 91e98
[4] J. Charvolin, Mol. Cryst. Liq. Cryst. 113 (1984) 1. [5] A. Saupe, Nuovo Cimento D Ser. 1 (1984) 16. [6] P.A. Winsor, in: G.H. Brown, M.M. Labes (Eds.), Liquid Crystals 3, Part I, vol. 43, Gordon and Breach, New York, 1972. [7] L.W. Reeves, A.S. Tracey, M.M. Tracey, J. Am. Chem. Soc. 9 (1973) 3799. [8] N. Boden, H.C. Holmes, Chem. Phys. Lett. 109 (1984) 76. [9] K. Radley, A.S. Tracey, Mol. Cryst. Liq. Cryst. Lett. 95 (1985) 1. [10] N. Boden, S.A. Corne, K.W. Jolley, Chem. Phys. Lett. 105 (1984) 99. [11] A.J.F. Bombard, I. Joekes, M.R. Alcantara, M. Knobel, Mater. Sci. Forum 416 (2003) 753. [12] M.R. Alcantara, E.G. Fernandes, Mol. Cryst. Liq. Cryst. 378 (2002) 89; 383 (2002) 37. [13] A.J.F. Bombard, I. Joekes, M.R. Alcantara, M. Knobel, J. Intel. Mater. Syst. Struct. 13 (2002) 471. [14] M.R. Alcantara, A.F. Moura, E.G. Fernandes, Liq. Cryst. 29 (2002) 191. [15] M.R. Alcantara, A.F. Moura, E.G. Fernandes, Mol. Cryst. Liq. Cryst. 333 (1999) 69. [16] N.K. Sanyal, R.A. Yadav, S.R. Shukla, Acoustica 59 (1986) 233. [17] N.K. Sanyal, R.A. Yadav, S.R. Shukla, Phys. Status Solidi A 99 (1987) 551. [18] S.N. Tiwari, R.A. Yadav, S.R. Shukla, N.K. Sanyal, in: B.K. Agrawal, H. Prakash (Eds.), Condensed Matter Physics, Narosa Publishing House, New Delhi, 1999, p. 182. Mr. M.K. Dwivedi is a Ph.D. student.
Dr. R.A. Yadav obtained his Ph.D. degree from Gorakhpur University, Gorakhpur and is presently working as Geophysicist. He has published more than fifteen research papers. His field of interest is liquid crystals.
Dr. S.N. Tiwari (Sugriva Nath Tiwari) obtained his M.Sc. and Ph.D. degrees in Physics from D.D.U. Gorakhpur University, Gorakhpur and is presently working as Reader in the Department of Physics, D.D.U. Gorakhpur University, Gorakhpur, India. He has been conferred ISCA Young Scientist Award in 1988. His research areas of interest are Material Science (Liquid Crystals), Molecular Biophysics, Biosensors and Radiation Biophysics. Dr. Tiwari has successfully completed two research projects and has published more than forty research papers in various national and international journals.