Rodlike molecule

Yoon K, Chae D G, Ree T and Ree F H 1981 Computer simulation of a grand canonical ensemble of rodlike molecules J. Chem. Phys. 74 1412-23... 

Altliough in figure C2.2.2 they are sketched witli rodlike molecules, botli nematic and chiral nematic phases can also be fonned by discotic molecules. 

Thennotropic liquid crystal phases are fonned by rodlike or disclike molecules. However, in the following we consider orientational ordering of rodlike molecules for definiteness, although the same parameters can be used for discotics. In a liquid crystal phase, the anisotropic molecules tend to point along the same direction. This is known as the director, which is a unit vector denoted n. 

Unwanted stmctures in the film plane—often found within LB films fonned from simple rodlike molecules or from molecules polymerized after deposition—can be problematic, since many possible applications of such films require a unifonn stmcture within the plane. On the other hand, however, the production of a system in which the stmcture within the plane is so disordered that there exist no stmctural features large enough to cause problems would also render applications possible. In tliree-dimensional materials, for example, both inorganic glasses and many polymers are capable of transmitting light without any appreciable scattering for substantial distances. 

Here, k provides a measure of the anisotropy in the well depth and for rodlike molecules is the ratio 8 1 where and Eg are the well depths when the molecules are side-by-side and end-to-end, respectively. The scaling parameter Eq is the well depth when the molecules are in the cross configuration as we can see by setting u, uj = u, f = uj f = 0 in Eqs. (4), (6) and (7). We should note that in the limit k and k tend to unity, that is x and x vanish then the Gay-Berne potential is reduced to the Leonard-Jones 12-6 potential. 

Since the parameter Rg is known to be a basic SEC size parameter for random-coil type molecules (Equation 4), and since it is also a well-defined statistical average size parameter, applicable to solutes of any shape including the sphere and rodlike molecules, Rg has been chosen in this work to serve as a common, reduced, solute-size parameter for describing the theory of SEC separation. By definition ... 

FIG. 2 Molecular orientation angles at liquid interfaces for rodlike molecules. The out-of-plane motion is a rotation away from the OZ axis, whereas the in-plane motion is performed with the OX, OY) plane. 

In a totally independent approach, highly fluorescent but rigid molecules can be used and their reorientational movement probed in solution, mostly by time-resolved fluorescence anisotropy, (85) For rodlike molecules likep-oligo-phenyls, this movement corresponds to the reorientation of the long molecular axis the length of which can be easily varied. 86 The use of fluorescence probes in liquid and solid media and on surfaces has been treated recently in several reviews and books. 87 ... 

Applequist and Mahr (114) proposed the use of Buckingham s equation (see the next subsection) for ellipsoids of revolution to calculate vacuum of rodlike molecules. They found for poly-L-tyrosine in quinoline that the values of 1/2 so computed from experiment varied linearly with molecular weight and yielded (4.94 0.014) D for fa. In this case, the molecular weights of the samples were indirectly estimated from the observed rotational relaxation times with the assumption of the relation for rigid rods. 

One potential application of the work on oriented nematic phases of rodlike molecules is to solutions containing cylindrical micelles. Orientation could be achieved by a shear field or perhaps by an electric field. Gotz and Heckman (9) confirmed the existence of anisotropic electrical conductivity for a concentrated surfactant solution in a shear field. They used their results to show that the solution contained cylindrical rather than platelike micelles. Of course, the magnitude of the electrical conductivity in an aqueous micellar solution should be quite different from that in the nematic phase of an organic material. So the conditions for and types of electrohydrodynamic instabilities could be different as well. 

Otani T, Araoka F, Ishikawa K, Takezoe H (2009) Enhanced optical activity by achiral rodlike molecules nano-segregated in the B4 structure of achiral bent-core molecules. J Am Chem Soc 131 12368-12372... 

Collagen VI is a rodlike molecule about 105-nm long with two globular regions at the extremities (Fig. 2A Furthmayr et al., 1983). The globular regions contain several domains homologous to von Willebrand... 

Fig. 5. Surface diffusion of the rigid rodlike molecule 4-trans-2-(pyrid-4-yl-vinyl) benzoic acid on Pd(110). In (a) and (b) two consecutive STM images taken at 361 K are shown which demonstrate the 1-dim motion. Arrows indicate molecules whose position changed circles mark fractionally imaged molecules moving under the STM tip in the course of the measurement, (c) Model for the flat adsorption geometry explaining the two observed molecular orientations in the STM data. The length of the molecule is 12.5 A. (d) Arrhenius plot of single molecule hopping rates [75].

The monomer-monomer correlation functions of flexible polyelectrolytes exhibit qualitatively the same behavior as those for rod-like molecules. The conformational changes, however, result in more pronounced and shifted peaks. From Fig. 8 we deduce a shift of the peaks of flexible chains to larger distances compared to those of rod-like chains. This is a consequence of a smaller overlap between flexible chains compared to the one between rodlike molecules. Naturally, the effect is most pronounced for densities larger than the overlap densities. The increased peak intensity corresponds to a more pronounced order in the system of flexible chains, and is a result of the more compact structure of a polymer coil. (The structural properties of flexible polyelectrolytes without medium-induced potential have been studied in [48].)... 

The property of viscosity is a very useful measure of the size and shape of a particle long thin molecules give rise to increased solution viscosity as opposed to small spherical molecules. This is because the drag force exerted by one macromolecule on another or on a neighboring water molecule is proportional to the surface area. The surface area of rods is greater than the surface area of an equivalent sphere and therefore rodlike molecules have a higher surface-to-mass ratio than do spherical ones. This also implies... 

Specifically, he developed relationships for the free energy of mixing of solvent and solute (polymer) molecules with different solute axial ratios (length/width) and solute interaction parameters. In the absence of interactions between solute molecules, the free energy of the system lowers when rodlike molecules precipitate out of solution and form a separate solid phase. This is due to the fact that small water molecules must order themselves around large rodlike macromolecules in solution and therefore the system is most stable when the water molecules and rodlike molecules are separated in space into different phases, such as liquid and solid phases. 

Correlated charge fluctuations between anisotropic bodies acting across an anisotropic medium create torques as well as attractions or repulsions. The formulae derived here for semi-infinite media can also be specialized to express the torque and force between anisotropic small particles or between long rodlike molecules. (For example, Table C.4 and Subsection L2.3.G.)... 

Liquid crystals consist of rigid rodlike molecules whose interaction tends to align them parallel to each other (for more details, see de Gennes, 1974 ... 

The major components of the membrane skeleton are spectrin, actin, and protein 4.1. Spectrin is a highly flexible, rodlike molecule composed of two nonidentical polypeptides a-spectrin and (3-spectrin.These chains are aligned side by side in the form of a a(3-heterodimer, and spectrin heterodimers in turn join head to head to form (aP)2-tetramers. The tail ends of spec-... 

FIG. 15.49 Orientation angle 6 between rodlike molecules, described by unit vector u and director n within one nematic domain of a macroscopically isotropic polydomain sample a denotes the size of the domain. From Beekmans, 1997. 

FIG. 15.50 Order parameters of rodlike molecules in the isotropic and the nematic states. Kindly provided by Prof. SJ. Picken (2003). 

The existence of liquid crystalline phases of rodlike molecules in solution becomes obvious if we simply consider the binary phase diagram of rigid rod-like low molar mass molecules or macroinolecules A in a suitable solvent S (Figure 2). Because of its chemical... 

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