Overall analysis of first‐order phase transitions in some alkyloxycyanobiphenyl liquid crystals

Abstract

Measurements of pressure, molar volume and specific heat as functions of temperature in the isotropic (I) phase as well as in the smectic A (SmA) and nematic (N) mesophases of some alkyloxycyanobiphenyl compounds (nOCB, n = 6–10) were carried out using differential thermal analysis under pressure, densitometry, X‐ray powder diffraction and modulated differential scanning calorimetry. Thermodynamic properties, such as latent heats and volume jumps at the different phase transitions, were determined. The coherence of this whole set of data was tested using pressure–temperature data through the slopes associated to their phase transitions, extrapolated at normal pressure in the light of the Clausius–Clapeyron equation.

Keywords:

• Clausius–Clapeyron equation
• molar volume
• odd–even effect
• pressure–temperature diagrams

Acknowledgements

The authors wish to express their gratitude for the financial support from the MCYT (project FIS2005‐00975) and the MEC (project MAT2006‐13571‐C02‐02) of Spanish Government, the DURSI (grant 2005SGR‐00535) from the Generalitat de Catalunya's Government and the Gobierno Vasco (grant IT‐484‐07).