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Influence of Ionic Interactions on the Photoinduced Birefringence of Poly[1-[4-(3-Carboxy-4 Hydroxyphenylazo) Benzene Sulfonamido]-1,2-Ethanediyl, Sodium Salt] Films

Ferreira, Q. ; Gomes, P. J. G. ; Raposo, M. R. ; Giacometti, J.A. Giacometti ; Oliveira, O. N. O. ; Ribeiro, P.A.

Sensors and Actuators, B: Chemical Vol. 7, Nº 8, pp. 2659 - 2666, August, 2007.

ISSN (print): 0925-4005
ISSN (online):

Scimago Journal Ranking: 1,45 (in 2007)

Digital Object Identifier: 10.1166/jnn.2007.621

Electrostatic interactions govern most properties of polyelectrolyte films, as in the photoinduced birefringence of azo-containing polymers. In this paper we report a systematic investigation of optical storage characteristics of cast and layer-by-layer (LbL) films of poly[1-[4-(3-carboxy-4 hydroxyphenylazo) benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). Birefringence was photoinduced faster in PAZO cast films prepared at high pHs, with the characteristic writing times decreasing almost linearly with the pH in the range between 4 and 9. This was attributed to an increased free volume for the azochromophores with the enhanced electrostatic repulsion in PAZO charged to a greater extent. In contrast, in LbL films of PAZO alternated with poly(allylamine hydrochloride) (PAH), the electrostatic interactions between the oppositely charged polymers hampered photoisomerization and molecular rearrangement, thus leading to a slower writing kinetics for highly charged PAH or PAZO.