Polymer light-induced mass transport

The photoinduction of optical anisotropy has been studied in a number of the supramolecular systems, as discussed in the previous part of the chapter. On the contrary, the choice of the supramolecular systems, in which the formation of SRG has been reported, is rather restricted. One of the reasons can be a prevailing opinion that the covalent bonding of azobenzene to polymer chain is a necessary condition for the effective light-induced mass transport. First attempts to inscribe SRG in the supramolecular system were performed on LbL films (see description of the LbL system in the previous part of this chapter), but the obtained gratings were not very deep. Although the applicability of the approach has been principally demonstrated, the obtained results rather supported the current opinion that the mass transport may be effective only in the covalently bound materials. That is why the very effective inscription of SRG in the spin-coated... 

Ionic complexes of polyelectrolytes and charged azobenzenes have optical response of the azobenzene, although influenced by the polymer matrix, as discussed earlier. The repeated E-Z isomerization is considered as a primer condition for the light-induced mass transport. Peculiar to the latter is the fact that the process is not more a local light-induced event but implies a translational motion of chromophores (Fig. 2.1). Moreover, the mass is transported only if the chromophores involve the passive polymer chains in their translation. This explains the high efficiency of SRG formation in functionalized polymers (Natansohn and Rochon, 2002 Viswanathan et al., 1999), why the covalent bonding has been considered as a necessary condition for the effective light-induced mass transport (Oliveira et al., 2005 Zucolotto et al., 2003 Fiorini et al., 2000 Viswanathan et al., 1999 ), and why the extremely effective SRG formation in the materials with ionic-bounded azobenzene (Kulikovska et al., 2007 Stumpe... 

---