Phase transition studies in N(p-n-pentyloxy benzylidene) p-n-decyl aniline

The temperature dependences of the molar volume, the ultrasonic velocity and the refractive index in N(p-n-pentyloxy benzylidene) p-n-decyl aniline, which exhibits nematic, smectic-A and smectic-B, phases, are presented. The isotropic-nematic and smectic-A-smectic-B phase transitions are found to be of first order while the nematic-smectic-A transition is of second order. The thermal expansion coefficient (a) computed from the molar volume data agrees with a second-order N-S_A transition. The computed adiabatic compressibility β_ad, molar sound velocity (or Rao number R_n ) and molar compressibility (or Wada constant A) are presented.     

Phase transition studies in N-(p-n-pentyloxy benzylidene) p-Toluidine

The variations of molar volume M_v and ultrasonic velocity V with temperature in N(p-n-pentyloxy benzylidene) p-toluidine are presented. The molar volume jump at the nematicisotropic transition suggests it is of first order. The adiabatic compressibility β _ad, molar sound velocity or Rao number R_n , molar compressibility or Wada constant A, the thermal expansion coefficient α, and Van der Waals constant b, are computed. Molar sound velocity and molar compressibility are compared with the values of other members of the homologous series and are found to be in good agreement with Rao's and Wada's observations. The order parameter S_k, at the nematic-isotropic phase transition is 0.441 from our experimental results and the Maier-Saupe table and is found to be in good agreement with the theoretical value.     

Ultrasonic investigations of N- (p-n-pentyloxybenzylidene) p-n-butylaniline

The ultrasonic velocity in N-(p-n-pentyloxybenzylidene) p-n-butylaniline is measured as a function of temperature from the isotropic liquid phase to the smectic G phase. A mixed smectic phase (S_AG) for a temperature interval of 2°C is reported. The derived parameters such as adiabatic compressibility (β_ad). Rao number (R_n) and molar compressibility (B) are also reported.     

Dielectric studies in N- (p-n-butoxybenzylidene) p-n-butylaniline

The dielectricconstant variation with temperature of N-(p-n-butoxybenzylidene)p-n-butylaniline is presented in the isotropic, nematic, smectic A and smectic B phases. A new transition in the nematic phase is reported. The derived parameter, molar susceptibility anisotropy, Δσ, is also determined.     

Phase transition studies in polymesomorphic compounds(v): Density studies in N-(p-n-Octyloxy benzylidene)-p-n-butyl aniline

The density, ρ, of N-(p-n-octyloxy benzylidene) p-n-butyl aniline (OBBA) is measured as a function of temperature from the isotropic liquid to the smectic-G phase. The compound is trimorphic, exhibiting three smectic phases, smectic-G, crystal smectic-B, and smectic-A phase. The changes in density across the phase transformations and the calculated thermal expansion coefficients confirm the order of the transitions as first order. Particular importance of the smectic-A to crystal smectic-B transformation, which is of first order, is apparent from the density jump across the transition.     

Ultrasonic study of molecular interaction in binary liquid mixtures at 30°C

Densities ρ and ultrasonic speeds u of the binary mixtures of tetrahydrofuran (THF) with 1-butanol and tert-butanol, at 30°C, over the entire composition range were measured. From these data isentropic compressibility, K _s, intermolecular free length L _f, relative association R _A, acoustic impedance Z, molar sound speed R _m, deviations in isentropic compressibility ΔK _s, and excess volume V ^E were calculated. The variation of these parameters with composition of the mixture helps us in understanding the nature and extent of interaction between unlike molecules in the mixtures. Further, theoretical values of ultrasonic speed were evaluated using theories and empirical relations. The relative merits of these theories and relations were discussed.     

Orientational order parameter studies on 3.Om and 3O.Om liquid crystals

Orientational order parameter S is evaluated in the nematic phase of six liquid crystal compounds, N-(p-n-propyl benzylidene)-p-n-alkoxy anilines, 3.Om and N-(p-n-propyloxy benzylidene)-p-n-alkoxy anilines, 3O.Om compounds with m = 6, 7 and 8, using different methods. The techniques employed are S from birefringence δn, Haller's approximation from (1?T/T_c) ^β, effective geometry parameter α_g and Vuks’ scaling factor S_C. The values of S obtained using the above methods are compared with one another and with the results on a number of liquid crystals; the liquid crystals favor isotropic Vuks’ method.     

Acoustical and excess properties of {1-hexanol + n-hexane, or n-octane, or n-decane} at (298.15, 303.15, and 308.15) K

Densities (ρ) and speeds of sound (u) for the binary mixtures of 1-hexanol with n-hexane, n-octane and n-decane have been measured over the entire composition range at 298.15, 303.15 and 308.15 K. The dynamic viscosities (η) for these systems have been measured at 298.15 K. From experimental data, excess molar volumes (V_m^E), molar isentropic compressibility (K_s,m), excess molar isentropic compressibility (K_s,m^E), deviation in speed of sound (u^D) from their ideal values (u^id) in an ideal mixture, and excess free volumes (V_f^E) have been calculated. The excess functions have also been correlated with the Redlich–Kister polynomial equation. The viscosity data have been analysed in terms of some semi-empirical equations. The theoretical values of speed of sound (u) and isentropic compressibility (κ_S) have also been estimated using the Prigogine–Flory–Patterson (PFP) theory with the van der Waals (vdW) potential energy model and the results have been compared with experimental values. The effect of chain-length of n-alkanes as well as the temperature on the excess properties has also been studied.     

Speeds of sound and isentropic functions of n-alkoxypropanol with 1-butanol and 2-butanol at 298.15 K

Speeds of sound have been measured as a function of composition for binary mixtures of propylene glycol monomethyl ether (1-methoxy-2-propanol), propylene glycol monoethyl ether (1-ethoxy-2-propanol), propylene glycol monopropyl ether (1-propoxy-2-propanol), propylene glycol monobutyl ether (1-butoxy-2-propanol), and propylene glycol tert-butyl ether (1-tert-butoxy-2-propanol), with 1-butanol, and 2-butanol, at 298.15 K and atmospheric pressure. The speeds of sound values were combined with those of our previous results for excess molar volumes converted to densities to obtain isentropic compressibility κ_S. Deviation in isentropic compressibility Δκ_S was evaluated using volume fraction weighting of the individual component properties to estimate ideal mixture behavior. The deviations u^D of the speed of sound from their values in an ideal mixture were also evaluated for all measured mole fractions. The speeds of sound results have been used to estimate the apparent molar isentropic compressibility at infinite dilution.     

Estimation of effective Debye temperature from sound velocity of N-(p-n-alkoxybenzylidene)-p-n-alkylanilines, (nO.m) liquid crystalline compounds

The ratio of specific heats (γ), Poisson's ratio (σ), effective Debye temperature (θ_D) collision factor (S_m), etc., are estimated in different LC phases of N-(p-n-alkoxybenzylidene)-p-n-alkylanilines, (nO.m's) liquid crystalline compounds using the density and sound velocity data. The variation of these parameters in different mesomorphic phases with the chain length is studied. The effective Debye temperature (θ_D), the collision factor (S_m) exhibits a similar variation with the alkyl chain length. Further, the space filling factor (r_fm) estimated using Kittel's formula is constant for all the materials irrespective of the phase with a value of 0.416. The molecular radius shows an increment of 0.074, 0.072 and 0.068 ? per CH₂ group in isotropic, nematic and smectic-A phases respectively in 5O.m series. Further, the specific heat ratio (γ) value is found to be lower in isotropic phase than in liquid crystalline phases. The data is compared with the body of the data in the literature.     

Computation and analysis of the dynamic structure factor S(k, ω) for small wave vectors

Molecular dynamics (MD) calculations have been performed for the Lennard-Jones (12-6) potential function using 2048 particles. Using conventional parameters the results may be compared with those for liquid argon.

The dynamic structure factor S(k, ω) has been determined both by Fourier inversion of the intermediate scattering function F(k, t) and from the longitudinal current-current correlation function C _∥(k, t). Particular attention was paid to the recurrence time of the system. The results for S(k, ω) by the two methods agree within 5 per cent for the whole region of small k-vectors considered. Double Fourier inversion of the van Hove function G(r, t) led to insufficiently accurate results for these small k-values. In view of the present data, the MD-results of Levesque et al. [1] for S(k, ω) have only a qualitative character. These latter data appear to contain truncation errors due to incomplete Fourier transformations.

Using a hydrodynamic assumption for F(k, t) we were able to extract the transport coefficients, the velocity of sound and the ratio of the specific heats in the limit of large wave lengths or small k. The velocity of sound was obtained by exploiting the MD generated anomalous dispersion curve of sound waves. Anomalous dispersion was found to set in for kσ ～ 0·25. A sound speed of 880 ms^-1 has been determined which is in excellent agreement with experimental values for liquid argon. The total error for the MD value amounts to about 5 per cent. In contrast, the ratio of the specific heats γ and the transport coefficients D _T and Γ (thermal diffusivity and sound attenuation) were determinable only with an accuracy of 15 per cent due to the need for larger extrapolations. Nevertheless, we found D _T, Γ and γ in agreement with experimental values within 5-10 per cent.     

Conductometric and thermodynamic studies on the ionic association of HCOONH4, phCOONH4, HCOONa and phCOONa in aqueous–organic solvents

The specific conductance of ammonium formate, ammonium benzoate, sodium formate and sodium benzoate in (10%, 20% and 30% (W/W)) methanol–water, ethanol–water and glycerol–water mixtures at different temperatures (293, 298, 303 and 308 K) was measured.The molar conductance (Λ), limiting molar conductance (Λ₀), limiting ionic conductance (λ₀), association constants (K_A), the activation energy of the transport process (E_a), Walden product (Λ₀η₀), hydrodynamic radii (1/r_s⁺ + 1/r_s⁻)^− 1, transfer numbers of the studied ions (t), standard thermodynamic parameters of association (ΔG_A, ΔH_A and ΔS_A) were calculated and discussed.The results show that, the molar conductance and the limiting molar conductance values were decreased as the relative permittivity of the solvent decreased while, the association constant increased. Also the results show that the molar conductance, the limiting molar conductance and the association constant values were increased as the temperature increased indicating that the association process is an endothermic one.     

Phase transition studies in polymesomorphic compounds

Summary The structural parameters of theS _A andS _B mesophases and the phase transitionS _G -S _B andS _B -S _A of the compound N-(p-n-octyloxybenzylidene)p-n-butyl aniline were investigated by X-ray diffraction. This work is complementary to the previous structural determination in the crystalline solid phase andS _G phase of the same compound. TheS _B hexagonal lattice parameters atT=66°C area=b=(5.03±0.01) ? andc=(27.6±0.2) ?. TheS _A structural data atT=80°C are layer thicknessd=(26.9±0.2) ? and intermolecular distanceD=(5.04±0.05) ?. The interlayer and the in-plane intermolecular distances were obtained as a function of temperature through all the mesophases. Pretransitional effects were observed at theS _G -S _B phase transition, which corresponds to a progressive reduction to zero of the molecule inclination angle with respect to the normal to the smectic layers. The layer thickness in theS _A phase appeared smaller than that in theS _B due to molecular axial fluctuations. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

Molecular magnetism of a linear Fe(III)-Mn(II)-Fe(III) complex. Influence of long-range exchange interaction

The magnetic properties of [L-Fe(III)-dmg₃Mn(II)-Fe(III)-L] (ClO₄)₂ have been characterized by magnetic susceptibility, EPR, and Mössbauer studies. L represents 1,4,7-trimethyl-, 1,4,7-triazacyclononane and dmg represents dimethylglyoxime. X-ray diffraction measurements yield that the arrangement of the three metal centers is strictly linear with atomic distancesd _Fe-Mn=0.35 nm andd _Fe-Fe=0.7 nm. Magnetic susceptibility measurements (3–295 K) were analyzed in the framework of the spin-Hamiltonian formalism considering Heisenberg exchange and Zeeman interaction:=J _Fe-Mn(S _Fe1+S _Fe2)S _Mn +J _Fe-Fe(S _Fe1 S _Fe2) +g_B S _total B. The spinsS _Fe1=S _Fe2 =S _Mn=5/2 of the complex are antiferromagnetically coupled, yielding a total spin ofS _total=5/2 with exchange coupling constantsF _Fe-Mn=13.4 cm^–1 andJ _Fe-Fe= 4.5 cm^–1. Magnetically split Mössbauer spectra were recorded at 1.5 K under various applied fields (20 mT, 170 mT, 4T). The spin-Hamiltonian analysis of these spectra yields isotropic magnetic hyperfine coupling withA _total/(g _{N N})=–18.5 T. The corresponding local componentA _Fe is related toA _total via spin-projection:A _total=(6/7)A_Fe. The resultingA _Fe/(g _NN)=–21.6 T is in agreement with standard values of ferric high-spin complexes. Spin-Hamiltonian parameters as obtained from Mössbauer studies and exchange coupling constants as derived from susceptibility measurements are corroborated by temperature-dependent EPR studies.     

The sound velocity of liquid TeSe mixtures

We have measured the sound velocity of liquid Te₇₀Se₃₀, Te₅₀Se₅₀ and Te₃₀Se₇₀ mixtures and obtained their adiabatic compressibility β_s. There appear prominent maxima in the temperature variations of β_S. It is concluded that the pressure-induced semiconductor-to-metal transition previously observed for liquid Te-Se mixtures is associated with the structural change from Se-like loosely packed to Te-like densely packed structure.     

Extension of the Launder,Reece and Rodi model on compressible homogeneous shear flow

This article describes the second order closure progress that was made to calculate compressible homogeneous shear flow with significant compressibility. Several DNS results show that compressibility has an important effect on the pressure-strain correlation. The term recognized as the principal responsible for the change in the magnitude of Reynolds-stress anisotropies. Thus, the pressure-strain incompressible models do not correctly predict compressible turbulence at high-speed shear flow. A method of including compressibility effects in the pressure-strain correlation is the subject of the present study. The concept of the growth rate of turbulent kinetic energy can be used to construct a compressible correction to the Launder, Reece and Rodi model for the pressure-strain correlation. This correction concerns essentially the C ₁,C ₃ and C ₄ coefficients which become in a compressible turbulence situation a function of the turbulent Mach number. The application of the new model shows good agreement with DNS results of Sarkar for cases A ₁, A ₂ and A ₃. These cases correspond to a moderate mean shear rate, so that nonlinear effects are important. This revised version was published online in July 2005 with corrections to some characters in the abstract.     

Spin observables in small-angle elastic → d scattering with an L-type deuteron target at 800 MeV

We have measured spin correlation parameters that describe the elastic scattering of 800 MeV polarized protons from an L-type polarized deuteron target at laboratory angles below 20°. The measured parameters include the correlated analyzing powers A_SL, A_LL and A_NLL and the proton spin-transfer coefficients C_0L,S, C_0L,L, C_SL,N, C_NL,S, C_NL,L and C_LL,N. The results are compared with single-scattering predictions based on different phase-shift solutions for the nucleon-nucleon scattering matrix.     

A new technique for determination of melting temperature of poly(ethylene glycol) by ultrasonic velocimetry

Ultrasonic velocity and density of poly(ethylene glycol) (PEG) (mol. wt. 2000 and 8000) solutions in water and benzene have been studied as a function of temperature from which respective isentropic compressibility has also been calculated. The velocity (as well as isentropic compressibility) undergoes a sudden change near melting temperature, T _m, of the solute polymer. Normally, we expect only one peak in viscoelastic properties at the T _m of PEG. However, we see two peaks (T _m1 and T _m2) in the case of the aqueous solution of PEG while there is only one peak for the case of benzene solution. This has been interpreted on the basis that one of the peaks (T _m1) is for unsolvated PEG and the other peak (T _m2) is that of PEG with water solvation shell. Such solvation shell is not formed with the aprotic solvent (benzene).     

X-ray diffraction of the smectic phases of N-(p-n-heptyloxybenzylidene)-p′-n-pentylaniline

Using X-ray diffraction the various smectic phases of N-($\text{p}$-$\text{n}$-heptyloxybenzylidene)-$\text{p}$′-$\text{n}$-pentylaniline can be classified (with increasing temperature) as S_H, S_B, S_C and S_A, respectively. The long molecular axes are probably tilted with respect to the normal to the layers in the S_A, S_C and S_H phases, and perpendicular to the layers in the S_B phase.     

Volumetric, acoustic and spectroscopic studies for binary mixtures of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) with alkoxyalkanols at T = (288.15 to 318.15) K

Densities and speeds of sound have been measured for the binary mixtures of ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF₆] with ethylene glycol monoethyl ether (EGMEE), diethylene glycol monoethyl ether (Di-EGMEE), triethylene glycol monoethyl ether (Tri-EGMEE) over the whole composition range at atmospheric pressure. Experimental densities have been used to estimate excess molar volumes, V^E. Changes in isentropic compressibility, Δκ_s have been estimated by using experimental speed of sound and density values. Excess properties were fitted to the Redlich-Kister polynomial equation to obtain the binary coefficients and the standard errors. The molecular scale interactions between ionic liquid and alkoxyalkanols have been investigated through ¹H NMR spectroscopy. NMR chemical shifts for hydroxyl group of alkoxyalkanols and their deviations show hydrogen bonding interactions of varying strengths between ionic liquid and alkoxyalkanol in their binary mixtures.