Molecular orientation effect

Their low melt viscosity permits molding of thin sections and complex shapes. However, their tendency to form ordered structures causes LC materials to be particularly susceptible to molecular orientation effects during processing. 

Fig. 25 Molecular orientation effects on FCP in lower-molecular-weight PS without medium (PS 148H)...

Wang Y, Cardona CM, Kaifer AE (1999) Molecular orientation effects on the rates of heterogeneous electron transfer of unsymmetric dendrimers. J Am Chem Soc 121 9756-9757... 

Application of cohesion energy parameters to interpreting surface phenomena requires additional caution. Steric hindrance and molecular orientation effects become very significant. The difference between the local cohesion energy parameter for one end of a molecule compared with the local cohesion parameter at the other end is often very large. For surface active agents it is customary to say that the one end is hydrophilic and the other end is very hydrophobic. For smaller molecules this difference from one end of the molecule to the other end may not affect interpretation of solubility phenomena, but can affect surface phenomena, for example. 

The key difficulty in developing this approach is the treatment of the influence of intramolecular correlations upon the site density, n fr). Recall from Section III.B that in the interaction site formalism, the explicit treatment of molecular orientation effects upon the correlation functions is replaced by a coupling of intramolecular and intermolecular correlations. For an inhomogeneous simple fluid, the molecular density may be written in the... 

Sokolowski and Steele have adapted the spherical harmonic expansion technique described in Section III.A to the calculation of the density profiles of nonspherical molecules in contact with solid surfaces. They have used the results to investigate molecular orientation effects in high temperature adsorption from the gas phase. The RAM theory described in Section III.E has been extended to the adsorption of fluids on solid surfaces by Smith et al. ° for hard-sphere interactions and by Sokolowski and Steele to the case of more realistic fluid-solid interactions. The principal deficiency of the approach is the accuracy of the predicted correlation functions for the bulk fluid which are required as input to the theory. 

Figure 5.2 shows molecular aggregate models examined in this study. We assume a A-type three-state monomer with the excitation energies of 10,000 and 30,000 cm and the transition moments of 5 D. The H- and L-shaped dimer models are also investigated in order to clarify. the molecular orientation effect on EIT. The excited states of the molecular aggregate models are calculated by solving Eq. 5.6 under the assumption of the dipole-dipole coupling between monomers. The excitation... 

This technique is suitable for amorphous materials, such as waxes, tarry solids, hot melt adhesives, and some low-melting solids. Rubbery materials often have a tendency to retract, since the applied pressure is normally only by hand, and the assembly may need to be clamped. For rubbers it is probably better to prepare a thin film by the melt method described in the section Hot compression molded films. This melt approach is not recommended for materials which will crystallize on solidification, since scatter and molecular orientation effects will lead to both poor spectral contrast and irreproduci-bility. 

The molecular model of an elastomeric network with local intermolecular correlations, given by Flory, is used to calculate the components of the molecular deformation tensor and molecular orientation. Effects of molecTilar parameters such as severity of entanglements, network inhomogeneities and conditions during cross-linking are discussed. Components of molecular deformation and orientation are calculated for a network under uniaxial stress. 

Hydrophobic interactions combined with H-bonding as well as specific molecular orientational effects at interfaces are probably the crucial topics for further exploration at the moment. 

Ohta et have investigated the molecular orientation effects on the TPA spectra, using J- and H-type dimers composed on three-state monomers. They have highlighted the structures that can lead to enhancement of the TPA intensities. 

Masao Oe used sum-frequency generation vibration spectroscopy to investigate the molecular orientation effect and found that the macromolecular main chains of PI are aligned at a slight angle towards the actual rubbing direction [47]. 

They have anisotropic finished-part properties molecular orientation effects are produced from melt flow diming molding. 

In Chapter 8 we will present a detailed discussion of the isotropic phase molecular orientation effects by an applied optical field from a short intense laser pulse. It is shown that both the response time and the induced order Q depend on the temperature vicinity (T-in a critical way they both vary as (r- which becomes very large near T. This near-r critical slowing down behavior of the order parameter Q of the isotropic phase is similar to the slowing down behavior of the order parameter S of the nematic phase discussed in the previous section. Besides the nematic isotropic phase transition, which is the most prominent order disorder transition exhibited by Uquid ciystals, there are other equally interesting phase transition processes among the various mesophases, such as smectic-A smectic-C, which will be discussed in Chapter 4. 

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