Deformational polarisability

Another example of the coupling between microscopic and macroscopic properties is the flexo-electric effect in liquid crystals [33] which was first predicted theoretically by Meyer [34] and later observed in MBBA [35], Here orientational deformations of the director give rise to spontaneous polarisation. In nematic materials, the induced polarisation is given by... 

Electric polarisation (P ef deformation, Por orientation polarisation) Momentum coordinate Spatial coordinate... 

Besides the orientation polarisation we observe a deformation polarisation, identical to that of an induced dipole moment. In a spatial unit the polarisation caused by deformation (due to a shift of the electrical charges) will be... 

For a system under elongational deformation along direction 1, for a beam of light propagating in direction 3, according to (10.17) one obtains different refractive indices for different polarisation of the beam, so that, for polarisation in directions 1 and 2, one has a difference of refractive indices... 

The polarisation itself is, just as the molecular polarisability is, the result of deformation polarisation Pd and the orientation polarisation Ps. Accordingly, the total polarisation is equal to P = Pd + Pa. Because of the resistance to motion of the atom groups in the dielectric, there is a delay between changes in the electric field and changes in the polarisation. The deformation polarisation takes place instantaneously (more precisely in a time of the order of 10-14 s) on the application of an electric field. There are two limiting values of e Erxi at short times or high frequencies and es at long times or low frequencies. This means that we have for the deformation polarisation... 

Definition of molecular mass averages, 17 Deformation flexural, 825 plastic, 830 polarisation, 325 properties, 824 uniaxial, 825 De Gennes... 

First consider the application of an external electric field to an assembly of rigid molecular dipoles, i.e. let there be no deformational polarisation. If the permanent moment of each dipole is /i, then the potential energy u of a dipole in the applied field will be ... 

Taking into account the possible anisotropy of the deformational polarisability of molecules requires that... 

Freezing of a dipolar liquid is accompanied by a rapid decrease in its electric permittivity [8-10]. Following solidification, dipole rotation ceases and the electric permittivity is almost equal to n, where n is refractive index, as it arises from deformation polarisation only. Investigation of the dynamics of a confined liquid is possible from the frequency dependences of dielectric properties, which allows both the determination of the phase transition temperature of the adsorbed substance and characteristic relaxation frequencies related to molecular motion in particular phases. 

The structural effects of Zn-doping in LaMni xZnx03, where 0 < x < 0.08, were revealed by shifts in IR and Raman bands from MnOfi deformations.247 Polarised Raman and IR reflection spectra were reported and analysed for HoMn03 single crystals.248... 

This simple model depends on the properties of a deformable core, and is only likely to be significant for heavier, polarisable metals. In addition, there are the directional influences of the valence orbital overlaps, which have been widely explored, and, in general, favour cis geometry in the d-block. For example, the Extended Huckel calculations of Tatsumi and Hoffmann show the dominant role of 4d-n orbitals in stabilising the cis geometry in MoO + [75]. In this... 

The numerator in this equation takes account of the contribution to non-ideality arising from the long range electrostatic forces obeying Coulomb s inverse square law, while the denominator takes account, in a rather crude manner, of the non-ideality introduced by short range forces when the ions come close together. This corresponds to the assumption that the ions are hard spheres, non-polarisable, non-deformable and spherically symmetrical, and manifests itself as the distance of closest approach, a. There are, of course, other short range... 

The physical basis of the Raman effect is related to deformation of electron shells of molecules in an electric field E determined by the molecular polarisability a. Because the laser beam can be considered an oscillating electromagnetic wave with the electrical vector E and a frequency v0 it induces during interaction with the sample the electric dipole momentum P = aE. This momentum is the driving force of the deformation of the electronic shells of the molecules. Because this deformation is periodical, the molecular dipoles begin to vibrate with a characteristic frequency vm. 

The performance of quasistatic work on closed systems is involved not only in deformation processes (change in volume, length and surface) but also in changes of electrical and magnetic properties (charge transfer, polarisation). 

Figure 1. a) Polarised extinction spectra of samples with Ag nanoparticles original sample and irradiated at 400 nm in the multi-shot regime (100 pulses in single spot), peak pulse intensity was 0.42 TW/cm2 b) TEM image of deformed nanoparticles after irradiation. The laser polarisation is shown as an arrow c) SAXS intensity distribution from the irradiated sample. The light ring in the centre is the shadow of the beam stop. 

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