The wavenumber shift of the isotropic and anisotropic profiles of the C O stretching mode of methyl ethyl ketone (MEK) was measured in several polar and non-polar solvents at different concentrations. The anisotropy shift function F = dn .2e + n 2 / 2 e −1 was plotted as a function of solute concentration (f). A discontinuity around 50% appears to be present in many solvent systems. The variation of shift with concentration may arise as a result of several interactions such as dipole-dipole, dipole-quadrupole, quadrupole-quadrupole and higher multipole interactions in the solute-solvent systems. The plot of lnF against f is linear over the entire range. It may be inferred from the data that repulsive-type intermolecular forces play a significant role in these molecular systems. The steric effects may be responsible for the discontinuity in the F vs f plot apart from the atomic quadrupole effects and other intermolecular forces.
The critical behaviour of the electroclinic response in the chiral smectic A * phase in the vicinity of the second-order smectic A * to smectic C * phase-transition temperature has been investigated using a new electro-optic technique. The temperature variation of the electroclinic coefficient, the relaxation frequency and the coefficient of the quartic term in the tilt angle in the Landau free energy expansion have been studied. The electroclinic coefficient diverges with decreasing temperature as the smectic A * to smectic C * phase-transition temperature is approached with a critical exponent, as predicted in the mean field Landau theory. The measured quartic coefficient varies strongly with temperature, contrary to the usual assumptions of the mean field Landau theory.
In a thermodynamical process, the dissipation or production of entropy can only be positive or zero according to the second law of thermodynamics. However the laws of thermodynamics are applicable to large systems in the thermodynamic limit. Recently a fluctuation theorem known as the Transient Fluctuation Theorem (TFT) which generalizes the second law of thermodynamics even for small systems has been proposed. This theorem has been tested in small systems such as a colloidal particle in an optical trap. We report for the first time an analogous experimental study of TFT in a spatially extended system using liquid crystals.PACS numbers: 05.70. Ln, 61.30.Gd The laws of thermodynamics describe the physical behaviour of macroscopic systems. The second law of thermodynamics states that when such a system is taken from one equilibrium state to another in a process, the change in entropy can only be positive or zero depending on wheather the process is irreversible or reversible respectively. Though the laws of thermodynamics are applicable under very general conditions, these laws are strictly valid only for large systems in the so-called thermodynamic limit. For these large systems, the effects of thermal noise on the average macroscopic physical quantities are not manifested except under special physical conditions such as near phase transitions. However, when the system size is small or more precisely the change in the relevant energy of the system in a process is of the order of the thermal energy k B T , k B being the Boltzmann constant and T being the absolute temperature of the system, the thermal noise is expected to play an important role on it's behaviour. In particular, the validity of the second law of thermodynamics for small systems is of considerable debate since the time of Boltzmann. Recently a nonequilibrium fluctuation theorem (FT) known as the Transient Fluctuation Theorem (TFT) has been proposed to generalize the second law of thermodynamics for these small systems [1]. In its most general form, TFT not only predicts transient violation of second law of thermodynamics when the dissipation is comparable to the thermal energy k B T but also it provides an expression for the probability that a dissipative flux flows in a direction opposite to that required by the second law of thermodynamics. More precisely for a thermostated system at temperature T , this theorem states that in a time interval τ , the probability P (Ω τ ) of a dissipation Ω τ being positive and the probability P (−Ω τ ) of same dissipation Ω τ being negative in an irreversible process satisfies the following conditionThe dissipation being an extensive quantity, the total dissipation increases as either the system size or the observation time is increased. Then the above theorem implies that the production of entropy or positive dissipation will be overwhelmingly more likely than the consumption of entropy or negative dissipation in an irreversible process for large systems or for large observation time in accordance with the sec...
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