Oriental stabilizers

The synthesis of materials for device applications has very different requirements. Here, the most important questions are What does the device do and what factors will affect its performance The magnitude of the desired optical nonlinearity will always be one of many criteria that will ultimately dictate the material of choice. In many instances the magnitude of the nonlinearity will not be the most important parameter. Depending on the device applications, other considerations such as optical transparency, processability, one- and two-photon optical stability, thermal stability, orientational stability, and speed of nonlinear response will all be important. Our current understanding of NLO materials suggests that these variables are frequently interrelated and that there is often no ideal NLO material. The material of preference for a given application will typically be one that is the best compromise for a variety of variables. Tutorials by G. Stegeman and R. Zanoni, and by R. Lytel outline some of the NLO device applications and the related materials issues. 

In order to assess the orientational stability of the poled state, the temperature dependence of the dipole mobility of the side groups was examined through dielectric relaxation measurements. (13) No low temperature relaxation below Tg was observed in the frequency range studied (100 Hz-100 kHz). In addition, the dielectric constant was approximately equal to the square of the refractive index, indicating that below T only electronic and no significant orientational contributions to the dielectric displacement are present. Thus, it was expected that a given orientational state of the ensemble would be stable at temperatures significantly below Tg. 

Molecular Length, Functional Group Placement, and Orientational Stability... 

It has also been shown that attachment of dyes to a crosslinked polymer network greatly improves orientational stability, especially when the dye itself... 

The materials studied displayed relatively low glass transition temperatures and therefore poor orientational stability. Future studies should be directed to solving this problem. Additional research is required to improve the efficiency of photoinitiation for materials with strong absorptions in the visible region of the spectrum. Other issues such as strain caused by shrinkage during crosslinking need to be addressed. 

This silver-catalyzed ring rearrangement could be explained by preferential interaction of the silver cation with the most substituted edge of the cyclopropane to form an argento cation. In the latter, the presence of C-Si or Ge bond with the right orientation stabilized the cation sufficiently so that it classically evolved through (3-H... 

Kig. 7. An orientation stability map for magnesia at 1400 °C. Each point corresponds to the orientation ofan observed grain. Faceted orientations are marked with an x and smooth orientations are marked with an empty square. An AFM image of a typical faceted surface is shown in the upper left hand part of the figure. The facets are approximately 500 A high. 

Fig. 15 Inverse pole figure summarizing reactivity and orientation stability data for titania.

Addition to conjugated alkenylbenzenes orientation. Stability of the benzyl cation... 

Liquid crystalline polyesters with 3-methylphthalimide and chromophore side chains, having good orientation stability and mechanical properties, were claimed for making nonlinear optical devices like filters, polarisers, waveguides and others [274]. 

Both the PAA-5 and the imidized form could be oriented by electrode poling. The former was poled by ramping the temperature slowly from 150-280°C (2 ). The decay of the orientated samples while heating at 37minute is shown in Figure 5. The lower orientational stability of the sample derived fi om the polyamic acid relative to the polyimide itself is believed to result from the lower cure temperature used for the former. Extrapolation of the decay curve from PI-5 poled at 300°C intersects the temperature axis aroimd 360°C which is close to the measured polymer Tg (i.e., 350°C). 

Henderson, S. A., and C. A. Koch. 1970. Co-orientation stability by physical tension a demonstration with experimentally interlocked bivalents. Chromosoma, 29 207-216. 

These practical considerations have led investigators away from simple guest-host polymer systems, perceived to have less intrinsic orientation stability, toward systems in which the nonlinear chromophore mobility is hindered. This can be achieved by chemically bounding the active molecules, in side- or in main-chain, or alternatively promoting cross-linking after orientation [17]. 

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