Smectic bilayer model

The most successful continuum description of membrane elasticity, dynamics, and thermodynamics is based on the smectic bilayer model (for examples of different versions and applications of this approach see Ref. 76-82 and references therein). We introduce this model in conjunction with the question of membrane undulations. 

A final example of the simulation of a complex system is a series of MD simulations of bilayer membranes. Membranes are crucial constituents of living organisms they are the scene for many important biological processes. Experimental data are known for model systems for example for the system sodium decanoate, decanol and water that forms smectic liquid crystalline structures at room temperature, with the lipids organized in bilayers. 

The earliest approach to explain tubule formation was developed by de Gen-nes.168 He pointed out that, in a bilayer membrane of chiral molecules in the Lp/ phase, symmetry allows the material to have a net electric dipole moment in the bilayer plane, like a chiral smectic-C liquid crystal.169 In other words, the material is ferroelectric, with a spontaneous electrostatic polarization P per unit area in the bilayer plane, perpendicular to the axis of molecular tilt. (Note that this argument depends on the chirality of the molecules, but it does not depend on the chiral elastic properties of the membrane. For that reason, we discuss it in this section, rather than with the chiral elastic models in the following sections.)... 

The Tokyo Tech group assigned a C2 structure for the layers in the B2 phase, and ferroelectric packing of such layers to form a locally polar C2v macroscopic structure, as indicated in Figure 8.20. Other early workers in the field also adopted this structural model for the B2 phase. Brand et al. had discussed a C2 smectic chevron structure in their 1992 theoretical study,29 and while they seem to be referring to an all-anticlinic bilayer smectic, their actual graphic is basically identical to that shown in Figure 8.20. Furthermore,... 

The Singer and Nicholson (13) model for the plasma membrane, which now receives much support, is basically a smectic liquid crystal consisting of one bilayer of phospholipid (Figure 4a). The phospholipid bilayer contains cholesterol at a concentration which depends on cell type. Embedded in the lipid liquid crystal he protein molecules. Some of these protein molecules transverse the entire lipid bilayer and communicate both with the inside and the outside of the cells. Some of these may... 

The studied compounds all have a terminal cyano group which means a very strong dipole. Cladis et al. [69] proposed a structural model of the bilayer smectic A phase for this kind of molecules (Fig. 3). The molecules are assumed to be associated in antiparallel pairs, which results in a weak interacting between the different polar parts of the pairs and a less dense packing of the molecules. Thus a transition of such bilayer SmA phase to a re-entrant nematic phase seems to be evident, because in this phase empty spaces of the structure are filled up more efficiently. Probably for similar reasons Pollmann et al. [70-72] found a pressure-induced re-entrant cholesteric phase behavior for ternary mixtures of cholesteryl n-alkanoates which, however, are terminally nonpolar (see Fig. 4). The mixtures of... 

In these copolymers, the segregation of two components into the bilayer really takes place however, the formed phase was a dissipative (frustrated) structure as can be seen from the X-ray diffraction pattern in Fig. 9.22a. In addition to the ordered position of the mesogen in the smectic layer cycle, there is a periodic density fluctuation from the undulations parallel to the layers. Figure 9.22b expresses the structural model. The undulations of the layer are due to a reverse domain structure of the polar structure of Fig. 9.21. We expected it to emerge in one... 

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