Study of the smectic-Ato hexatic–smectic-Btransition in the binary systemn-hexyl-4’-n-pentyloxybiphenyl-4-carboxylate and 4-propionylphenyl-trans(4-n-pentyl)cyclohexane carboxylate (original) (raw)
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Journal of Physics D: Applied Physics, 2008
The nematic (N) to smectic A (SmA) phase transitions in binary mixtures of the 6th (D6AOB) and 7th (D7AOB) members of alkylazoxybenzene series have been studied using high-precision calorimetry at 10, 20, 30, 50, 75 and 100 wt% of D7AOB concentrations. The temperature range of the nematic phase on six binary mixtures was wide, and it was dependent on the concentration of D7AOB and the ratio of transition temperatures T NA /T NI changes from 0.889 for 10 wt% D7AOB to 0.951 for 100 wt% D7AOB. The ratio of specific-heat amplitudes above and below the nematic to smectic (NA) transition, A + /A − , remains ∼1.0. The value of specific-heat exponent, α, changes from 0.1 to 0.4, implying variations from three-dimensional Ising type behaviour to mean field tricritical type behaviour, respectively, when the concentration of D7AOB increased from 10 wt% to 100 wt%.
Physical Review E, 2010
The continuous nematic to smectic-A (N -SmA) phase transition has been studied by highresolution ac-calorimetry in binary mixtures of the liquid crystal octylcyanobiphenyl(8CB) and a non-mesogenic, low-molecular weight, solvent n-hexane(hex) as a function of temperature and solvent concentration. Heating and cooling scans about the N -SmA transition temperature were repeatedly performed on pure and six 8CB+hex samples having hexane molar concentration ranging from x hex = 0.02 to 0.12. All 8CB+hex samples in this range of x hex remain macroscopically miscible and exhibit an N -SmA heat capacity peak that shifts non-monotonically to lower temperature and evolves in shape, with a reproducible hysteresis, as x hex increases. The imaginary part of heat capacity remains zero up to x T CP hex ≃ 0.07 above which the distinct peak is observed, corresponding to a jump in both the real and imaginary enthalpy. A simple power-law analysis reveals an effective exponent that increases smoothly from 0.30 to 0.50 with an amplitude ratio
Quasicritical heat capacity at a smectic-A–hexatic-B phase transition
Physical Review E, 1997
High-resolution ac calorimetry has been used to characterize the excess heat capacity ⌬C p (T) associated with the smectic-A (SmA) -hexatic-B (HexB) transition in n-hexyl-4Ј-n-pentyloxybiphenyl-4-carboxylate ͑65OBC͒. For temperature oscillations in the investigated frequency range 1.42-400 mHz, the ⌬C p data reveal no frequency dependence and correspond to static thermodynamic values. The present data resolve several discrepancies in previously reported C p values. This transition is very weakly first order, but power-law fits could be made to ⌬C p . Such fits yield an effective critical exponent ␣ eff ϭ0.65Ϯ0.05, which agrees quite well with values of ϳ0.6 reported by Huang and co-workers ͓Phys. Rev. Lett. 46, 1289 ͑1981͒; Phys. Rev. A 28, 2433 ͑1983͒; Phys. Rev. Lett. 56, 1712 ͑1986͔͒. Such an exponent value disagrees strongly with the theoretically predicted three-dimensional XY value ␣ XY ϭϪ0.007. It is proposed that this C p behavior and also the reported order parameter variation, which yields an effective critical exponent  eff of ϳ0.2, are consistent with quasitricritical or quasitetracritical ͑strain-smeared, very weak first-order͒ behavior arising from a coupling between the amplitude of the bond-orientational order and the in-plane positional strain.
Physical Review E, 1995
I Two compounds of the 1-{4'-alkoxyphenylamino-3-[5"-{2"-menthylpirydil)]-propen-1-one-3 (PIRn) series that exhibit the hexatic-B (Hex-B) to smectic-A (Sm-A) and the crystal-8 (Cry-B) to Hex-B phase transitions were studied by high resolution ac calorimetry. The Hex-B-Sm-A phase transition was found to be of first order and continuous for PIR7 and PIR9, respectively. The tricritical point was located at the concentration for which Tery~H, "z/THe"z sm z =0.980+0.004, i.e. , a hexatic range of 7 K. At both sides of the tricritical point, nonclassical and non-three-dimensional-XY specific heat exponents a were observed. The Cry-B-Hex-B phase transition was of first order and was associated with a small or immeasurable C~a nomaly.
Physical Review A
The binary-mixture phase diagram of n-propyl-4'-tt-dmyloxybiphenyl-4-carboxylate [3(10)OBC] aud n-butyl-4'-n-decy1oxybiphenyl-4-carboxylate [4(10)OBC] has been investigated by optical microscopy"x-ray diffraction, and heat-capacity studies. Here 3(10}OBCand 4(10)OBC have the isotropic (I)smectic-A (Sm A)hexatic-B and I-Sm Asmectic-I (Smlw transition sequence, respectively. This binary-mixture study reveals two new features, namely, the existence of the hexatic-B-SmI transition and a Sm Ahexatic-8-SmI point where the relevant three phases coexist.
Chemical Physics Letters, 2003
The two-component system octylcyanobiphenyl(8CB) + decylcyanobiphenil(10CB) has been studied by means of Modulated Differential Scanning Calorimetry, optical microscopy and X-ray diffraction. Although the general trends of the phase diagram are similar to that proposed by Marynissen et al., additional evidences for the existence of TCP have been reported, the composition being about 0.2, which is slightly lower than that proposed in the aforementioned work. Additionally, the smectic mesophase of the 8CB + 10CB mixtures has been characterised through X-ray diffraction and optical measurements as smectic A for the whole composition range. Such a result is against the recent work of Oweimreen and Hwang.
Journal de Physique, 1982
2014 Les densités des mélanges binaires de 4,4'-dipentylazoxybenzène (DPAB) et 4-éthyl-4'-pentylazoxybenzène (EPAB) avec 4-pentyl-4'-cyanobiphényle (PCB) pour les concentrations moyennes et dans l'intervalle des températures 25-80 °C sont mesurées. Les volumes isothermes de mélange des solutions Vs (égaux aux volumes d'excès VE, en cas d'existence des deux composants dans la même phase que la solution) sont aussi calculés à partir des interpolations de volumes molaires. Les coefficients isobares de dilatation thermique, pour un mélange de EPAB + PCB sont aussi calculés. La présence de complexes molaires de type A-B est confirmée. Abstract.-Densities of binary mixtures of 4,4'-dipentylazoxybenzene (DPAB) and 4-ethyl-4'-pentylazoxybenzene (EPAB) with 4-pentyl-4'-cyanobiphenyl (PCB) were measured over the temperature range of 25 to 80 °C and in the middle area of concentrations. Isothermal volumes of mixing Vs (equal to the excess volume VE when both pure components and solution are in the same phase) were also calculated from interpolated molar volumes. Isobaric thermal expansion coefficients were also calculated for one of the mixture concentrations EPAB + PCB. The presence of a molecular A-B complex has been confirmed.
Physical Review A, 1987
The critical heat capacity associated with the nematic (N) to smectic-A (SmA) phase transition has been studied in mixtures of nonpolar heptyloxypentylphenylthiolbenzoate (7S5) and polar octyloxycyanobiphenyl (8OCB). In this system, which exhibits both an N-SmA-SmC multicritical point and an N-Sm A tricritical point, the N-SmA transition temperature T» increases very rapidly as the 8OCB mole fraction X is increased. Data were obtained for a sample near the tricritical composition, for two compositions where the N-SmA transition is second order, and for three compositions exhibiting weakly-first-order transitions. Because of the large values of dT» /dX, Fisher renormalization was observed. The finite cusp in C~n ear the tricritical point yields the renormalized critical exponent aq-0.93+0. 17. Since aq-u /(1a), this corresponds to a=0.48+0.05, in good agreement with the value 0.5 expected at a Gaussian tricritical point.
Physical Review E, 2018
Experimental and theoretical studies of a smectic-A-hexatic-B trasition in freely suspended films of thickness 2-10 µm of the 54COOBC compound are presented. X-ray investigations revealed a discontinuous first-order transition into the hexatic phase. The temperature region of two phase coexistence near the phase transition point diminishes with decreasing film thickness. The width of this temperature region as a function of the film thickness was derived on the basis of a Landau mean-field theory in the vicinity of a tricritical point (TCP). Close to TCP the surface hexatic-B order penetrates anomalously deep into the film interior.
Study of the isotropic to smectic-A phase transition in liquid crystal and acetone binary mixtures
The Journal of Chemical Physics, 2010
The first-order transition from the isotropic ͑I͒ to smectic-A ͑Sm A͒ phase in the liquid crystal 4-cyano-4Ј-decylbiphenyl ͑10CB͒ doped with the polar solvent acetone ͑ace͒ has been studied as a function of solvent concentration by high-resolution ac-calorimetry. Heating and cooling scans were performed for miscible 10CB+ ace samples having acetone mole fractions from x ace = 0.05 ͑1 wt %͒ to 0.36 ͑10%͒ over a wide temperature range from 310 to 327 K. Two distinct first-order phase transition features are observed in the mixture whereas there is only one transition ͑I-Sm A͒ in the pure 10CB for that particular temperature range. Both calorimetric features reproduce on repeated heating and cooling scans and evolve with increasing x ace with the high-temperature feature relatively stable in temperature but reduced in size while the low-temperature feature shifts dramatically to lower temperature and exhibits increased dispersion. The coexistence region increases for the low-temperature feature but remains fairly constant for the high-temperature feature as a function of x ace . Polarizing optical microscopy supports the identification of a smectic phase below the high-temperature heat capacity signature indicating that the low-temperature feature represents an injected smectic-smectic phase transition. These effects may be the consequence of screening the intermolecular potential of the liquid crystals by the solvent that stabilizes a weak smectic phase intermediate of the isotropic and pure smectic-A. Downloaded 02 Nov 2010 to 130.215.103.190. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights\_and\_permissions 174501-2 K. P. Sigdel and G. S. Iannacchione J. Chem. Phys. 133, 174501 ͑2010͒ Downloaded 02 Nov 2010 to 130.215.103.190. Redistribution subject to AIP license or copyright; see http://jcp.aip.org/about/rights\_and\_permissions