Electrical response properties, intermolecular

The linear polarizability, a, describes the first-order response of the dipole moment with respect to external electric fields. The polarizability of a solute can be related to the dielectric constant of the solution through Debye s equation and molar refractivity through the Clausius-Mosotti equation [1], Together with the dipole moment, a dominates the intermolecular forces such as the van der Waals interactions, while its variations upon vibration determine the Raman activities. Although a corresponds to the linear response of the dipole moment, it is the first quantity of interest in nonlinear optics (NLO) and particularly for the deduction of stracture-property relationships and for the design of new... 

In the last years we devoted considerable effort to understand the properties of pp chromophores in different environments. The basic idea is that pp chromophores respond largely and non-linearly to electric fields, being them externally applied field, or internal fields generated by the interaction with the surrounding. In this section we will briefly review our work on NLO responses of pp chromophores and on their spectroscopic behavior in solution. This work set the stage for building up models for mm based on pp chromophores, where intermolecular electrostatic interactions dominate the physics of the material. 

Equation (1) indicates that, in order to comply with the second law, the volume of a material must decrease upon isothermal compression. The precise maimer, however, in which a material reduces its volume in response to an applied pressure is unspecified by the second law and requires consideration on a molecular level. Molecular attributes such as bond angles, bond lengths, covalency, coordination number, and intermolecular forces can be influenced by pressure. Since these attributes are responsible for defining chemical, electrical, optical, and magnetic properties, pressure is a potentially powerful probe of the properties of materials. 

This study compared methacrylate and acrylate polymers to structural analogs with fluorinated ester groups. Two types of relaxations were characterized, the primary relaxation associated with the glass transition and secondary relaxations associated with side group motion and localized segmental motion. Dielectric analysis was used to characterize the response of dipoles to an electric field as a fimction of temperature. Mechanical properties were analyzed via dynamic mechanical analysis and stress relaxation measurements. Relaxation behavior was interpreted in terms of intermolecular and intramolecular mechanisms. 

The interactions of uncharged species have been touched upon above. Since the van der Waals forces dominate these interactions, they will be discussed at length in the final section of this chapter. It suffices here to say that these forces arise from the frequency-dependent electric and magnetic susceptibilities of the interacting species, and it is precisely these susceptibilities which are responsible for the spectral properties of the molecules comprising the particle. Thus, molecular (or chemical) specificity of particle interaction forces is of central importance. From another standpoint, this can be understood by considering an individual molecule as the limiting case of a particle. Then for the intermolecular van der Waals force to be consistent as two such particles (molecules) approach to the point of orbital overlap, their interaction must reduce to the relevant chemical interaction force which is fundamentally dependent upon chemical specificity. 

Liquid crystals (LCs) represent an intermediate state of matter between the solid and liquid phases, often referred to as the fourth state of matter, and exhibit the regularity of crystalline solid and the fluidity of isotropic liquid [1-4], The unique thermal, mechanical, optical, and electrical properties of LCs originate from the molecular self-organization facilitated by weak intermolecular interactions, which is sensitive to external stimuli. Stimuli-responsive LCs are at the forefront in the development of electro-optic devices such as LC displays (LCDs) and continue to attract great interest in view of both fundamental research and practical applications. 

Even if not directly observable, intermolecular forces influence the microscopic and bulk properties of matter, being responsible for a variety of interesting phenomena such as the equilibrium and transport properties of real fluids, the structure and properties of liquids and molecular crystals, the structure and binding of Van der Waals (VdW) molecules (which can be observed under high resolution rotational spectroscopy [5-8] or molecular beam electric resonance spectroscopy [9]), the shape of reaction paths and the structure of transition states determining chemical reactions [10]. 

Several methods have been developed in order to determine the macroscopic optical properties [63], of which the simplest is the oriented gas model due to Chemla et al. [64, 65] In that method, the hnear and nonlinear susceptibilities (Eq. (8.2) are calculated from simple tensor sums of the (hyper)polarizabihties of the molecules constituting the elementary unit cell. Corrective factors can subsequently be added to account for the effects of local electric fields. The relevance of this method is ensured provided the intermolecular interactions are weak, while the macroscopic responses are strongly dependent on the values of local field factors. More sophisticated schemes take into account the intermolecular interactions. They include the supermolecule model [66-69], where an aggregate of... 

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