Molecular orientation hybrid

Ashwell GJ, Berry M (2005) Hybrid SAM/LB device structures manipulation of the molecular orientation for nanoscale electronic applications. J Mater Chem 15 108-110... 

W. Zheng, C.-Y. Chiang, I. Underwood, Hybrid molecular orientation of sandwich-type structure discogen hexaalkoxydibenzo[a, c]phenazine on the surfaces modified using silane self-assembled monolayers. Mol. Cryst. Liq. CrysL 540, 94-101 (2011)... 

Fig. 4.18 Molecular orientation in Nisseki LC Film Series. (a) Twisted orientation, (b) hybrid orientation, (c) homeotropic orientation...

Neither does the microbrownian motion of the amorphous mesh inhibit the liquid crystal phase, nor does the positional order of the molecules interfere with the elasticity. Hence, as a hybrid material that combines LC and rubber characteristics, LCEs have unique properties in which the molecular orientation of the liquid crystal is strongly correlated with the macroscopic shape (deformation) which is unparalleled to other materials. The most prominent example in the physical properties derived from this property is the huge thermal deformation. Figure 10.1 shows an example of the thermal deformation behavior of side-chain nematic elastomers (NE) [3]. When the molecules transform from the random orientation in the isotropic phase to the macroscopic planar orientation in the nematic phase, the rubber extends in the direction of the liquid crystal orientation and increases with decreasing temperature as a result of an increase in the degree of liquid crystal orientation. This thermal deformation behavior is reversible, and LCEs can be even considered as a shape-memory material. Figure 10.1 is from a report of the early research on thermal deformation of LCEs, and a strain of about 40 % was observed [3]. It is said that LCEs show the largest thermal effect of all materials, and it has been reported that the thermal deformation reaches about 400 % in a main-chain type NE [4]. 

FIGURE 3.16 Three common hybridization schemes shown as outlines of the amplitude of the wavefunction and in terms of the orientations of the hybrid orbitals, (a) An s-orbital and a p-orbital hybridize into two sp hybrid orbitals that >oint in opposite direc tions, forming a linear molecular shape, (b) An s-orbital and two p-orbitals can blend together to give three ip hybrid orbitals that point to the corners of an equilateral triangle, (c) An s-orbital and three p-orbitals can blend together to give four sp hybrid orbitals that point to the corners of a tetrahedron. 

Using Valence Bond (VB) theory, the central atoms of the molecules with formulas AB2U2 and AB3U should undergo sp3 hybridized with predicted bond angles of 109.5°. If no hybridization occurs, bonds would be formed by the use of p orbitals. Since the p orbitals are oriented at 90° from each other, the bond angles would be 90°. Note that hybridization is only invoked if the actual molecular geometry data indicate that it is necessary. 

The GHO basis can therefore provide a localised, directional set of orbitals (hybrids) which do not have the principal qualitative disadvantage of the usual hybrid sets they can be mutually orientated in any directions. What is more the directions taken up by the GHOs can be decided variationally and not by the unitary properties of a hybridisation matrix . This conclusion means that the use of a GHO basis provides both a localised bonding picture and simultaneously a theoretical validation of the VSEPR rules. Thus, it is not necessary, for example, to contrast the hybrid method and the VSEPR method for molecular geometries (30) they are complementary. 

Various novel imprinting techniques have also been presented recently. For instance, latex particles surfaces were imprinted with a cholesterol derivative in a core-shell emulsion polymerization. This was performed in a two-step procedure starting with polymerizing DVB over a polystyrene core followed by a second polymerization with a vinyl surfactant and a surfactant/cholesterol-hybrid molecule as monomer and template, respectively. The submicrometer particles did bind cholesterol in a mixture of 2-propanol (60%) and water [134]. Also new is a technique for the orientated immobilization of templates on silica surfaces [ 135]. Molecular imprinting was performed in this case by generating a polymer covering the silica as well as templates. This step was followed by the dissolution of the silica support with hydrofluoric acid. Theophylline selective MIP were obtained. 

A second common type of orbital hybridization involves the 2s orbital and only two of the three 2p orbitals (2a). This process is therefore referred to as sp hybridization. The result is three equivalent sp hybrid orbitals lying in one plane at an angle of 120° to one another. The remaining 2px orbital is oriented perpendicular to this plane. In contrast to their sp counterparts, sp -hybridized atoms form two different types of bond when they combine into molecular orbitals (2b). The three sp orbitals enter into a bonds, as described above. In addition, the electrons in the two 2px orbitals, known as n electrons, combine to give an additional, elongated n molecular orbital, which is located above and below the plane of the a bonds. Bonds of this type are called double bonds. They consist of a a bond and a n bond, and arise only when both of the atoms involved are capable of sp hybridization. In contrast to single bonds, double bonds are not freely ro-... 

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