Poling temperature

Fig. 26. Correlation between increment of spontaneous polarization from 80° C to 15° C and piezoelectric strain constant at room temperature for /9-form polarized poly(vinylidene fluoride) films. Poling temperature = 90° C. Poling field = 700 kV/cm (Murayama, 1972)...

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. 

In the limit of the oriented gas model with a one-dimensional dipolar molecule and a two state model for the polarizability (30). the second order susceptibility X33(2) of a polymer film poled with field E is given by Equation 4 where N/V is the number density of dye molecules, the fs are the appropriate local field factors, i is the dipole moment, p is the molecular second order hyperpolarizability, and L3 is the third-order Langevin function describing the electric field induced polar order at poling temperature Tp - Tg. 

Atmospheric carbon dioxide is the source of Mars s polar ice caps. Atmospheres act like giant insulators for planets, preventing heat from radiating away to space. Mars s thin atmosphere holds very little heat—a blazing summer day on Mars might get up to the freezing point of water 32 E (0 C), but at night the temperature plummets well back below 0 E (18 C). At the poles, temperatures drop well below -lOO E (-73 C), sufficiently cold for the carbon dioxide in the atmosphere to freeze. Mars s polar ice caps consist of frozen carbon dioxide with an underlayer of ice. 

Typical values for = 1 cm and a = 100 /iw, for which Vf, set is in the 4-6 kV range for poling temperatures 25-150"C. This estimate corresponds to what is observed in practice for the wire-to-plane poling geometry. 

Fig. 12. Comparison on E-O coefficient of NLO polymers incorporated with non-dendritic chromophore 16 and dendritic chromophore 17 at different poling temperatures (12% wt. of chromophore in APC, 1.0 MV cm of poling field)...

In all techniques the chromophore orientation is frozen by cooling the poled film to the room temperature under the applied external field (Fig. 24) or by thermal or photocrosslinking during the poling procedure. In the case of thermal crosslinking it is important to tightly control the poling temperature and to in-... 

Fig. 28. Temporal variation of the order parameter < 2>of a polymethacrylate PMA3 (T = 97 °C) at different poling temperatures [169]...

Because of its simplicity, the oriented gas model relies on a large number of simplifications and approximations (i) at the poling temperature the chromophores are assumed free to rotate under the influence of the applied field and any coupling... 

Figure 9. Effect of poling temperature on thermal discharge currents for the 16-mol % ZnCl2 in PPO (field strength 2 kV/cm, heating rate...

Midlatitude storms are driven by equator-to-pole temperature contrast. In a warmer world, this contrast will probably weaken since surface temperatures in high latitudes are projected to increase more than at the equator (at least in the Northern Hemisphere). Higher in the atmosphere, however, the temperature contrast strengthens. Increased atmospheric water vapor could also supply extra energy to storm development. Which of these factors would be more important and how midlatitude storms would change in frequency, intensity, or location are not known at present. 

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