Polyimides optical functionality

Figure 8. TEM and optical absorption of the sample implanted with 5 x 10 Au /cm (a) TEM cross-sectional micrograph (dashed lines represent the free surface and film-substrate interface) (b) nanoparticles size distribution (c) simulated optical spectra (1) Au cluster in a non-absorbing medium with n = 1.6 (2) Au cluster in polyimide (absorbing) (3) Au(core)-C(shell) cluster in a nonabsorbing medium with n = 1.6 (4) the experimental spectrum of Au-implanted polyimide sample, (d) X-ray diffraction patterns as a function of the implantation fiuence.

Although there have been great advances in covalent functionalization of fullerenes to obtain surface-modified fullerene derivatives or fullerene polymers, the application of these compounds in composites still remains unexplored, basically because of the low availability of these compounds [132]. However, until now, modified fullerene derivatives have been used to prepare composites with different polymers, including acrylic [133,134] or vinyl polymers [135], polystyrene [136], polyethylene [137], and polyimide [138,139], amongst others. These composite materials have found applications especially in the field of optoelectronics [140] in which the most important applications of the fullerene-polymer composites have been in the field of photovoltaic and optical-limiting materials [141]. The methods to covalently functionalize fullerenes and their application for composites or hybrid materials are very well established and they have set the foundations that later were applied to the covalent functionalization of other carbon nanostructures including CNTs and graphene. 

On the one hand, linear aromatic polyimides have been generally used as electronic and aerospace materials because of their excellent mechanical strength, thermal, chemical and electronic/optic properties compared with other common amorphous polymers. Polyimides are also excellent membrane materials for gas separation due to their rigid chemical structures, allowing the production of larger functional free volume. Over the... 

Yang, S., Peng, Z., and Yu, L., Functionalized polyimides exhibiting large and stable second-order optical nonlinearity, Macromolecules, 27, 5858-5862 (1994). 

Yu, D., Gharavi, A., and Yu, L., A generic approach to functionalizing aromatic polyimides for second-order nonlinear optics. Macromolecules, 28, 784-786 (1995). 

Fig. 2.5 In-plane orientation function f, of an 8CB monolayer as a function of the rubbing-induced optical retardation T, induced in the polyimide orientation layer. Reproduction by permission from [22].

Table 12 lists the properties of this PI with those of PMDA-TFDB for comparison. In spite of the presence of electron-withdrawing -CF3 substituents, the maintained reactivity of TFDB is most likely based on the m a-substitution onto benzidine. If the (7r /i(7-substituted diamine counterpart was used, it must be difficult to obtain high molecular weight PAA in the conventional way because of its expected much lower reactivity. The transmission spectra of a series of TFDB-based Pis in Fig. 58 indicate how the 6FDA-TFDB polyimide film is optically transparent. A secondary positive effect of the -CF3 substituents in TFDB on the film transparency is the weakened intermolecular cohesive force due to lower polarizability of the C-F linkage. This functions negatively to interchain CTC formation. 

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