Nematic-isotropic transition transition

Camp P J, Mason C P, Allen M P, Khare A A and Kofke D A 1996 The isotropic-nematic transition in uniaxial hard ellipsoid fluids coexistence data and the approach to the Onsager limit J. Chem. Phys. 105 2837-49... 

Disc-like particles can also undergo an Onsager transition—here tire particles fonn a discotic nematic, where tire short particle axes tend to be oriented parallel to each other. In practice, clay suspensions tend to display sol-gel transitions, witliout a clear tendency towards nematic ordering (for instance, [22]). Using sterically stabilized platelets, an isotropic-nematic transition could be observed [119]. 

One prominent example of rods with a soft interaction is Gay-Berne particles. Recently, elastic properties were calculated [89,90]. Using the classical Car-Parrinello scheme, the interactions between charged rods have been considered [91]. Concerning phase transitions, the sohd-fluid equihbria for hard dumbbells that interact additionally with a quadrupolar force was considered [92], as was the nematic-isotropic transition in a fluid of dipolar hard spherocylinders [93]. The influence of an additional attraction on the phase behavior of hard spherocylinders was considered by Bolhuis et al. [94]. The gelation transition typical for clays was found in a system of infinitely thin disks carrying point quadrupoles [95,96]. In confined hquid-crystalline films tilted molecular layers form near each wall [97]. Chakrabarti has found simulation evidence of critical behavior of the isotropic-nematic phase transition in a porous medium [98]. 

The SD is a phase separation process usually occurring in systems consisting of more than two components such as in solutions or blends. However, in the present case the system employed is composed of one component of pure PET. In this case, what triggers such an SD type phase separation Doi et al. [24, 25] proposed a dynamic theory for the isotropic-nematic phase transition for liquid crystalline polymers in which they showed that the orientation process... 

Kinetics of isotropic-nematic phase transition of liquid crystals (Doi s theory)... 

The distribution of chain sequence extension, calculated by using RIS models, is compared with isotropic-nematic transition characteristics for a number of thermotropic polymers comprising rigid groups connected by polymethylene spacers. The distribution depends strongly not only on the odd-even character of the number of methylene units of the spacers, but also on the specific groups (or atoms connected at the ends of polymethylene spacers. 

Values of enthalpy and entropy change at isotropic-nematic transitions... 

A) Onsager s rigid-rod model (1949) was the first correct model of an athermal Isotropic —> Nematic phase transition. It is a relatively simple model that predicts phase transitions. It is based on excluded volume between two rigid rods, which reads... 

Conformational Changes Coupled with the Isotropic-Nematic Transition... 

The high degree of cooperativity that is characteristic of the helix-coil transition is not a prerequisite for coupling of a conformational change with the isotropic-nematic transition, although it may serve to accentuate the effect. Significant effects may be expected in other circumstances. 

Figure 11.5 Complex dynamic viscosity as a function of temperature for a main-chain polyether consisting of a methyl stilbene mesogen and a mixture of seven-and nine-carbon aliphatic spacers. The polymer has a molecular weight of 36,000. The diamonds and squares are for temperature ramp rates of 0.1 °C and 2.0°C/min, respectively the open and closed symbols are for heating and cooling, respectively. The dashed line marks the isotropic-nematic transition. (From Gillmor et al. 1994, with permission from the Journal of Rheology.)...

Rzoska, S. J., and Drozd-Rzoska, A. (2002) On the tricritical point of the isotropic - nematic transition in a rod-like mesogen hidden in the negative pressure region, in NATO Sci. Series II, vol. 84, Liquids under negative pressures, eds. lime, A. R., Maris, H. J., and Williams P. R. (Kluwer-Springer, Dordrecht) p. 116... 

When the isotropic-nematic transition occurs the concentration of rods changes abruptly and the order parameter jumps from zero to a value Sc. 

DYNAMICS OF THERMOTROPIC LIQUID CRYSTALS ACROSS THE ISOTROPIC-NEMATIC TRANSITION AND THEIR SIMILARITY WITH GLASSY RELAXATION IN SUPERCOOLED LIQUIDS... 

A. Dynamics across the Isotropic-Nematic Phase Transition... 

Figure 12. Orientational dynamics of the discotic system GBDII (N = 500) at several temperatures across the isotropic-nematic transition along the isobar at pressure P — 25. (a) Time evolution of the single-particle second-rank orientational time correlation function in a log-log plot. Temperature decreases from left to right, (b) Time dependence the OKE signal at short-to-intermediate times in a log-log plot. Temperature decreases from top to bottom on the left side of the plot T = 2.991,2.693,2.646, and 2.594. The dashed lines are the simulation data and the continuous lines are the linear fits to the data, showing the power law decay regimes at temperatures. (Reproduced from Ref. 115.)...

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