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

Abstract

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

Azopolymer triggered electrophoretic deposition of MnO2-carbon nanotube composites and polypyrrole coated carbon nanotubes for supercapacitors

“…The surface roughness can result from gas evolution during deposition, related to the electrochemical decomposition of water. 29,35 The spectrum of the deposited PAZO is similar to that of the protonated form of PAZO, prepared in acidic conditions. 5E and F).…”

“…The SEM studies of the lms prepared from aqueous solutions showed signicant surface roughness (Fig. 29,35 The peaks (Fig. The surface roughness can result from gas evolution during deposition, related to the electrochemical decomposition of water.…”

Mechanisms of adsorption of an azo-polyelectrolyte onto layer-by-layer films

“…The graph of Fig. 2 shows the spectra of (PAH/PAZO) LbL films with different number of bilayers obtained for PAZO adsorption time of 30 s. Plotting the maximum absorbance as a function of the number of bilayers for the LbL films prepared with different adsorption times, one can observe that the films grow linearly with the number of bilayers as is usual in LbL films [9,11]. The slopes of the fitted straight lines are proportional to the PAZO adsorbed amount per bilayer and from the obtained extinction coefficient the PAZO adsorbed amount per unit of area in each bilayer can be estimated.…”

“…In the present case, for PAZO concentrations higher than 0.003 M, a saturation of the adsorbed amount is observed indicating that an adsorbed amount of about 1.7 mg/m 2 is sufficient to compensate the substrate electrical charges where PAZO is being adsorbed. It should be remarked here that PAZO at pH 10 presents a high degree of charging [9] which suggest that electrostatics interactions are mainly accounting for the adsorption. The PAZO adsorbed molecules create a repulsing potential barrier, as predicted by Boöhmer et al [20], avoiding that more PAZO molecules are being adsorbed in this regime.…”

“…As suggested [7,8], the kinetics curves should be obtained by doing only one immersion per layer using different adsorption periods of times, being the kinetics curves the adsorbed amount per layer as a function of immersion time. This was the procedure adopted in this work, to investigate the mechanisms involved on the adsorption kinetics of a PAZO layer, a high degree of charge polyelectrolyte [9], onto already deposited PAH/PAZO LbL films during different periods of time, under different adsorption conditions as solution concentration and drying process. In this article, the mechanisms involved in the adsorption of one PAZO layer onto PAH/PAZO LbL films are discussed which explain the two processes, nucleation and diffusion, which are occurring during the PAZO adsorption.…”