Thermal poling

To study the polymer structural effects on PAP, including the size of the chromophore and the mode of connection of the chromophore to the main chain, SHG-PAP studies have been performed both on a true side hain polyimide system in which the chromophore is attached to the polymer backbone via flexible tedier (PI-3a in Figure 8.4 Tg = 228 C), and on donor-embedded polyimide syst s (PI-1 and PI-2 in Figure 8.4 Tg = 350 and 252°C, r pectively), in which the azo chromophore is incorporated into the polymer backbone through the donor substituent without any flexible connector or tether. Details of SHG-PAP can be found in reference 14. In both the side-chain and the donor-embedded polyimides, polar order can be generated by thermal poling... 

Similar PID results have been reported in very high Tg (up to SSO C) azo-polyimides. It has been shown previously that irradiation of the donor-embedded polyimide derivatives with polarized light alone at room temperature induces a quasi-permanent nonpolar orientation, which can be thermally erased only by heating the polymer above Tg. While, the lifetimes of the polar order generated by thermal poling of the donor-embedded polyimides were found to be on the order of tens of years to centuries at room temperature, photoisomerization can efficiently depole these polymer films in a matter of minutes at room temperature. Indeed, Figure 8.6 shows the effect of p-polarized irradiation on the SH signal of PI-2, which had been previously thermally... 

FIG. 10.7 Photo-thermal poling set-up. Poling voltage modulation is synchronized with the translation. Local illumination (He-Ne laser, 2 mW, 543 nm) provides heat to reach (Reprinted from ref. 76). Copyright 2002, American Institute of Physics. 

This paper presents details of a new, low-cost, continuous process in which pellets of poly(vinylidene fluoride) (PVDF) are directly converted into piezoelectric tube. Kawai s paper in 1969 (1 ) described a batch process for making PVDF piezoelectric by stretching filmB at an elevated temperature and subsequently applying a high electric field to the electroded and heated films (thermal poling). Since then many variations of this technique have been described. Southgate in 1976 (2) demonstrated that... 

For removing the centrosymmetry from polymer films containing non-linear-optical polar azo dyes such as DRl, this photo-electropoling technique (PEP) has emerged as an important method. In contrast to the usual thermal poling process (TP), PEP presents two major advantages for... 

In the case of thermal poling, electrodes are evaporated on to the PVDF and a field of 0.4-1.4 MV/cm is applied at temperatures of 90-100°C for 1 hr. Cooling with the field maintained stabilizes the polar orientation of the crystallites and produces permanent polarization (poling). 

Blanchard PM, Mitchell GR. 1993a. A comparison of photoinduced poling and thermal poling of azo dye doped polymer films for second order nonlinear optical applications. Appl Phys Lett 63(15) 2038 2040. 

Sekkat Z, Kang C S, Aust EF, Wegner G, Knoll W. 1995a. Room temperature photo induced poling and thermal poling of a rigid main chain polymer with polar azo dyes in the side chain. Chem Mater 7(1) 142 147. 

A peculiar specificity of the thermal energy compared to other energy varieties is that the capacitive relationship is not exactly the same. It differs mainly in the respective roles of the two capacitive state variables, basic quantity and effort, which are symmetrically swapped. For instance, the simplest model that corresponds to an ideal thermal pole uses the same exponential function as in the other energy varieties, but in a reversed way. In other words, this is the reciprocal relationship, called elastive relationship, that is written with the exponential function instead of the capacitive one in aU other varieties. 

Special treatment is required for the thermal energy variety. In this variety, the capacitive relationship is reversed as explained in case study A9 in Chapter 4 describing the thermal pole. The thermal capacitive relation does not use a scaling tanperature 7 but a scaling entropy identified with the Boltzmann constant... 

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