Effect of carbon nanotubes on the isotropic to nematic and the nematic to smectic- A phase transitions in liquid crystal and carbon nanotubes composites |
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Authors: | K P Sigdel G S Iannacchione |
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Institution: | Department of Physics, Worcester Polytechnic Institute, Worcester, Massachusetts 01609, USA. kps@wpi.edu |
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Abstract: | A high-resolution ac-calorimetric study on the weakly first-order isotropic to nematic (I -N and the continuous nematic to smectic-A (N -SmA phase transitions of the liquid crystal octyl-cyanobiphenyl (8CB) doped with well-dispersed multiwall carbon nanotubes (CNTs)
as a function of CNT concentrations is reported. Thermal scans were performed for all samples having CNT weight fraction from
fw \phi_{{w}}^{} = 0.0005 to 0.0060 over a wide temperature range well above and below the two transitions in pure 8CB. Both the I -N and the N -SmA transitions evolve in character and have their transition temperatures qualitatively offset by ∼ 1.10 K lower as compared
to that in pure 8CB for all 8CB+CNTs samples. The enthalpy change associated with each phase transition is essentially the
same as that of pure 8CB and remains unchanged with increasing fw \phi_{{w}}^{} . However, there is an evidence that the thermal transport properties of the composites differ from the pure LC upon cooling
below a fw \phi_{{w}}^{} -dependent temperature within the nematic phase. In addition, a new Cp feature is resolved for intermediate fw \phi_{{w}}^{} samples that appears to be correlated to this onset temperature. |
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