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It has been widely recognized that the combination of carbon nanotube (CNT) and liquid crystals (LCs) not only provides a useful way to align CNTs, but also dramatically enhances the order in the LC phases, which is especially useful in liquid crystal display (LCD) technology. As the measure of this phase behavior, the complex specific heat is presented over a wide temperature range for a negative dielectric anisotropy alkoxyphenylbenzoate liquid crystal (9OO4) and CNT composites as a function of CNT concentration. The calorimetric scans were performed under near-equilibrium conditions between 25 and 95°C, first cooling and then followed by heating for CNT weight percent ranging from ɸw = 0 to 0.2. All 9OO4/CNT mesophases have transition temperatures ~1 K higher and a crystallization temperature 4 K higher than that of the pure 9OO4. The crystal phase superheats until a strongly first-order specific heat feature is observed, 0.5 K higher than in the pure 9OO4. The transition enthalpy for the nanocomposite mesophases is 10% lower than that observed in the pure 9OO4. The strongly first-order crystallization and melting transition enthalpies are essentially constant over this range of ɸw. Complementary electroclinic measurement on a 0.05 wt. % sample, cooling towards the smectic-C phase from the smectic-A, indicates that the SmA-SmC transition remains mean-field-like in the presence of the CNTs. Given the homogeneous and random distribution of CNTs in these nanocomposites, we interpret these results as arising from the LC-CNT surface interaction pinning the orientational order uniformly along the CNT, without pinning the position of the 9OO4 molecule, leading to a net ordering effect for all phases. These effects of incorporating CNTs into LCs are likely due to "anisotropic orientational" coupling between CNT and LC, the change in the elastic properties of composites and thermal anisotropic properties of the CNTs. [ABSTRACT FROM AUTHOR]

High-resolution calorimetry has been performed to study the effect of dilution by a nonmesogenic, low-molecular weight solvent (linear n-hexane) on the isotropic-nematic (I-N) phase transition in the liquid crystal (LC) octylcyanobiphenyl (8CB) as a function of n-hexane concentration. Numerous temperature scans were performed without continuous mixing for pure 8CB and all mixture samples of n-hexane mole fraction ranging from xhex=0.02 to 0.12. The I-N specific heat peak remains first-order for all samples and shifts toward lower temperature nonlinearly while the two-phase I+N coexistence width broadens linearly with increasing xhex. Multiple heating and cooling scans are reproducible and indicate phase separation, if it occurs, must be on very short length scales and is reversible. These results may be a consequence of a competition between random dilution effects and the tendency to phase separate. It is shown that solvent dilution of a LC, if miscible and depending on solvent structure, can lead to a controlled altering of the intermolecular potentials and softening of the LC viscoelastic properties. [ABSTRACT FROM AUTHOR]

The microscopic properties of the inner surface of the cavities of Anopore and Nuclepore membranes are investigated with scanning electron microscopy (SEM), nitrogen adsorption isotherms, and deuterium nuclear magnetic resonance (2H-NMR). Useful information about the cavity orientation and morphology, and internal surface area is obtained. Analysis of SEM photographs yields estimates of the surface area and the porosity of these membranes which complements the adsorption results. The orientation of liquid crystals permeated in the cavities of Anopore and Nuclepore membranes is probed with the 2H-NMR technique. It is found that the orientation of the liquid crystal molecules is governed by the confining volume and surface conditions. The 2H-NMR spectral line shape of the confined liquid crystal also provides information on the substrate morphology and roughness that is consistent with SEM and adsorption experiments. [ABSTRACT FROM AUTHOR]

A high-resolution calorimetric study of the specific heat (Cp ) has been carried out for the isotropic to nematic phase transition in an aligned liquid crystal (octylcyanobiphenyl - 8CB) and aerosil nano-colloid gel. A stable alignment was achieved by repeated thermal cycling of the samples in the presence of a strong uniform magnetic field, which introduces anisotropy to the quenched random disorder of the silica gel. In general, the specific heat features of the I-N transition in aligned (anisotropic) gel samples are consistent with those seen in random (isotropic) gel samples, namely the observance of two Cp peaks and non-monotonic transition temperature shifts with increasing silica concentration. However, larger transition temperature shifts with silica density, modification of the phase conversion process in the two-phase coexistence region, and a larger effective transition enthalpy are observed for the aligned samples. The lower-temperature aligned Cp peak is larger and broader while exhibiting less dispersion than the equivalent peak for the random gel. This may be a consequence of the alignment altering the evolution from random-dilution-dominated to random-field-dominated effects. The exact origin of the larger transition temperature shifts is uncertain but the larger enthalpy suggests that the nematic state is different in the aligned system than in random gels. The general non-monotonic behaviour of the transition temperature is interpreted using dimensional analysis as a combination of an effective elastic stiffening of the liquid crystal combined with a liquid crystal and aerosil surface interaction energy. [ABSTRACT FROM AUTHOR]

High resolution calorimetric studies have been carried out on the chiral compound methylheptyloxydifluorooctyloxybenzoyloxytolane (8BTF2O1M7). The tilt tendency is greater in this compound than in several other structurally similar fluorinated tolane liquid crystals, and it exhibits tilted chiral smectic C(SmC*) and tilted twist-grain-boundary (TGBC) phases but not the untilted SmA or TGBA phases. The data confirm the presence of two tilted TGBC phases denoted TGB1 and TGB2. The TGB1-TGB2 first-order transition exhibits considerable hysteresis and a very small latent heat. There is no rounded excess heat capacity peak in the cholesteric N* phase associated with the non-transitional evolution of a chiral line liquid N*L, although such a feature has been observed in other fluorinated tolanes with a smaller tilt tendency. [ABSTRACT FROM AUTHOR]

A high resolution a.c. calorimetric study of a phenyl pyrimidine derivative with one alkyl and one perfluorinated end group shows that the excess heat capacity associated with the smectic A-smectic C transition exhibits critical fluctuation behaviour that is consistent with the three-dimensional XY universality class. This is in contrast to the usual mean-field SmA-SmC behaviour and the near tricritical fluctuation behaviour reported recently in several other compounds. It is speculated that smaller than usual correlation lengths are the cause for the wide fluctuation region in this compound. [ABSTRACT FROM AUTHOR]