Electric field poled

Figure I. Schematic representation of statistical orientational distribution functions in isotropic (I) and nematic (N) potentials. Dashed curves depict adjusted distributions under electric field poling.

H. Karlsson and F. Laurell, Electric field poling of flux grown KTiOPQ, Applied Physics Letters 71(24), 3474-3476 (1997). 

In view of the potential technological importance of noncentrosymmetric organic crystals, several approaches have been evolved to artificially achieve noncentrosym-metry, which include electric field poling of polymers, self-assembly of molecular layers, Langmuir-Blodgett assembly of films and host-guest interaction in noncentrosymmetric hosts (Marder et al, 1994). Prediction and/or control of the three-dimensional structure of crystals, given only the information of molecular properties, however, remains difficult at present. 

The experimental methods utilized here, as is generally the case for electric-field poling, measure the Z-component of the vector component of the hyperpolarizability, Pz (equation 4),... 

Three synthetic approaches to donor-acceptor-substituted conjugated molecules with enhanced orientability in electric fields, potentially applicable to the preparation of electro-optic polymers via electric field poling, are summarized. The three approaches are parallel attachment of chromophores to a common framework, embedding the chromophore in a zwitterion, and head-to-tail oligomerization of chromophores. The oligomerization method as well as the use of dyes as curing agents are briefly discussed in relation to the stability of electric field-induced polar order in polymer matrices. 

We decided to explore the possibility of performing electric field poling of a NLO-active compound at room temperature and solidifying the material by in-situ photopolymerization. In essence, instead of cooling the sample below Tg, we proposed to raise the Tg of the material above the poling temperature. This paper reports on systems in which the active NLO species is present either as a dopant in a photocrosslinkable host matrix or as the matrix itself. We also describe the preparation and use of several new donor-acceptor stilbene compounds similar to 1. 

Electric Field Poling and Photocrosslinking of Host/Guest Systems... 

Typical values of electrical properties of the homopolymer without additives and treatments are in the Table 3.8. The values can be substantially changed by the type of cooling and post-treatments, which determine the morphological state of the polymer. Dielectric constants as high as 17 have been measured on oriented samples that have been subjected to high electrical fields (poled) under various conditions to orient polar crystalline form.74... 

In electric-field poling, a guest dipolar chromophore and a chemically and optically passive host polymer (the chromophore can also be covalently tethered to the polymer [74] or incorporated into the main chain of the polymer) is heated to above the glass transition temperature, Tg, of the mixture. A large electric... 

For dipolar chromophores that are the subject of this chapter, only one component of the molecular hyperpolarizability tensor, Pzzz, is important. Thus, the summation in Eq. (8) disappears. Electric field poling induces Cv cylindrical polar symmetry. Assuming Kleinman [12] symmetry, only two independent components of the macroscopic second-order nonlinear optical susceptibility tensor... 

Chromophores must be thermally robust enough to withstand temperatures encountered in electric field poling and subsequent processing of chromophore/polymer materials. Chromophore decomposition temperatures can be assessed by techniques such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). TGA and DSC measurements on neat chromophore samples in air will tend to yield decomposition temperatures lower than those for the same chromophores in hardened polymer lattices. Typically, to be useful for development of device quality materials, a chromophore must exhibit thermal stability of 250 °C or higher (with thermal stability defined as... 

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