Calorimetric study of the nematic to smectic-A phase transition in octylcyanobiphenyl-hexane binary mixtures - Condensed Matter > Soft Condensed MatterReport as inadecuate




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Abstract: The continuous nematic to smectic-A N-SmA phase transition has been studiedby high-resolution ac-calorimetry in binary mixtures of the liquid crystaloctylcyanobiphenyl8CB and a non-mesogenic, low-molecular weight, solventn-hexanehex as a function of temperature and solvent concentration. Heatingand cooling scans about the N-SmA transition temperature were repeatedlyperformed on pure and six 8CB+hex samples having hexane molar concentrationranging from x {hex}= 0.02 to 0.12. All 8CB+hex samples in this range ofx {hex} remain macroscopically miscible and exhibit an N-SmA heat capacity peakthat shifts non-monotonically to lower temperature and evolves in shape, with areproducible hysteresis, as x {hex} increases. The imaginary part of heatcapacity remains zero up to x^{TCP} {hex}\simeq 0.07$ above which the distinctpeak is observed, corresponding to a jump in both the real and imaginaryenthalpy. A simple power-law analysis reveals an effective exponent thatincreases smoothly from 0.30 to 0.50 with an amplitude ratioA^{-}-A^{+} ightarrow 1 as x {hex} ightarrow x^{TCP} {hex}. This observedcrossover towards the N-SmA tricritical point driven by solvent concentrationis consistent with previous results and can be understood as weakening of theliquid crystal intermolecular potential promoting increased nematicfluctuations.



Author: Krishna P Sigdel, Germano S Iannacchione

Source: https://arxiv.org/







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