Molecular liquids, bond orientational ordering

Figure 3. (a) Two-dimensional, bond orientational order parameter average values in the molecular fluid layers of LI ecu confined in a multi-walled carbon nanotube of diameter D=9norder parameter values for the contact, second, third and fourth layers, respectively. The dotted line represents the bulk solid-fluid transition temperature, (b) Positional and orientational pair correlation functions in the unwraiqred contact layer of U CCU confined in a multi-walled carbon nanotube of diameter D=9.1< (5 nm) showing liquid phase at 7=262 K and crystal phase at 7=252 K. 

In this chapter, the results of the molecular-dynamies simulation of Ni, Cu and Au in liquid and supercooled liquid states are displayed. The potentials of interatomie interaction within the framework of the embedded-atom method are used to generate realistic atomic configurations. The struetural analysis of the eluster stmeture has been conducted with the use of the bond orientational order parameter of the interatomic bonds. It is shown that the loeal ieosahedral order is present and it enhances at supercooling of the melts of the metals imder discussion. 

FIGURE 1.5. Local two-dimensional lattice for (a) a liquid and (b) for a hexatic phase with bond-orientational order. The molecular centers of mass are denoted by dots. 

Smectic liquid crystals are distinguished by having an intermediate degree of positional order in addition to molecular orientational and, in some cases, bond orientational order. 

We observed an extraordinary enhancement in bond orientational order, in ultrathin films deposited below their glass transition temperature, as revealed by extraordinary high values of the dielectric strength with respect to the bulk [1]. By varying the deposition conditions and the molecular size, we could tune the kinetic stability of the liquid phase enriched in bond orientational order (MROL) towards conversion into the ordinary liquid phase. 

Upon cooling, the molecules in proximity of the LFSs assume a correlated orientation, forming regions characterized by medium range order. These regions, called medium range crystalline ordered regions (MCRO), are surrounded by amorphous liquid. The extent of molecular orientation within the MRCOs is quantified by the bond orientational order parameter, for which the hexatic form described by Eq (1) is assumed. 

Mesophases of supermolecular structure do not need a rigid mesogen in the constituent molecules. For many of these materials the cause of the liquid crystalline structure is an amphiphilic structure of the molecules. Different parts of the molecules are incompatible relative to each other and are kept in proximity only because of being linked by covalent chemical bonds. Some typical examples are certain block copolymers50 , soap micelles 51 and lipids52. The overall morphology of these substances is distinctly that of a mesophase, the constituent molecules may have, however, only little or no orientational order. The mesophase order is that of a molecular superstructure. 

While this general approach has been frequently exploited in MLCs, in fact, complex mesogen symmetries (less than cylindrical) and internal molecular flexibility (rotation about chemical bonds), renders eqn(l) only a coarse indicator of long-range orientational order in the liquid crystal. This is compounded in PLCs of the type shown in Figures 1 and 2 as the idealization of the mesogenic monomers is further complicated by their connectivity in the polymer. In... 

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