Order of phase transitions and tricriticality in mixtures of octyloxycyanobiphenyl and nonyloxycyanobiphenyl liquid crystals: A high-resolution study by adiabatic scanning calorimetry

We review results of a high resolution systematic study of the specific heat for alkyl-cyanobiphenyl liquid crystals confined to the 0.2µm diameter cylindrical pores Anopore membranes. The nematic director alignment at the pore wall is varied from homeotropic to tangential by pore surface treatment. Several phenomena are uncovered by these studies which probed the weakly first order nematic to isotropic, the continuous smectic-A to nematic and the first order smectic-A to isotropic phase transitions. The specific heat is strongly dependent on the nematic director configuration, and confinement effects are remarkably distinct according to the order of the phase transition. The influence of elastic distortions and surface ordering and disordering effects are evident. Despite considerable departures from bulk behavior with regards to specific heat peaks size, rounding and width, and transition temperature shifts, a bulk-like critical behavior appears to be retained. The formation of smectic translational order within the pores is hindered for those liquid crystals that also possess a nematic phase. The average scalar order parameter temperature dependence is extracted from the specific heat results using a simplified Landau-de Gennes type of model, and is shown to be consistent with nuclear magnetic resonance results.

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Chapter 13. High Resolution Adiabatic Scanning Calorimetry and Heat Capacities

Heat Capacities ◽

10.1039/9781847559791-00287 ◽

2010 ◽

pp. 287-306 ◽

Cited By ~ 12

Author(s):

Jan Thoen

Keyword(s):

High Resolution ◽

Heat Capacities ◽

Scanning Calorimetry ◽

Adiabatic Scanning Calorimetry

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Phase Transitions of Binary Lipid Mixtures: A Combined Study by Adiabatic Scanning Calorimetry and Quartz Crystal Microbalance with Dissipation Monitoring

Advances in Condensed Matter Physics ◽

10.1155/2015/479318 ◽

2015 ◽

Vol 2015 ◽

pp. 1-14 ◽

Cited By ~ 13

Author(s):

P. Losada-Pérez ◽

N. Mertens ◽

B. de Medio-Vasconcelos ◽

E. Slenders ◽

J. Leys ◽

...

Keyword(s):

Phase Transitions ◽

Phase Diagrams ◽

Quartz Crystal Microbalance ◽

Quartz Crystal ◽

Phase Behaviour ◽

Scanning Calorimetry ◽

Departure Point ◽

Peltier Element ◽

Adiabatic Scanning Calorimetry ◽

Lipid Mixtures

The phase transitions of binary lipid mixtures are studied by a combination of Peltier-element-based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM-D). pASC, a novel type of calorimeter, provides valuable and unambiguous information on the heat capacity and the enthalpy, whereas QCM-D is proposed as a genuine way of determining phase diagrams by analysing the temperature dependence of the viscosity. Two binary mixtures of phospholipids with the same polar head and differing in the alkyl chain length, DMPC + DPPC and DMPC + DSPC, are discussed. Both techniques give consistent phase diagrams, which compare well with literature results, showing their capability to map the phase behaviour of pure lipids as well as lipid mixtures. This work can be considered as a departure point for further investigations on more complex lipid mixtures displaying relevant phases such as the liquid-ordered phase and solid-lipid interfaces with biologically functional importance.

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