In situ UV–vis absorbance measurements for Langmuir films of poly[4′-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13) azopolymer

• Published in: Journal of colloid and interface science 2004-08, Vol.276 (1), p.138-142
• Main Authors: dos Santos, D.S, Pavinatto, F.J, Balogh, D.T, Misoguti, L, Oliveira, O.N, Mendonça, C.R
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2004.03.027

In situ UV–vis absorbance measurements are used to investigate aggregation in Langmuir films from the azopolymer poly[4′-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13), a methacrylate derivative of DR13. The level of aggregation in a Langmuir film is intermediate between that of HPDR13 in chloroform solution and in a deposited LB film, as expected. Absorption is negligible at large areas per monomer, and starts to increase at a critical area that is the same as the one obtained in surface potential isotherms, being close to twice the area per monomer for a condensed film. This indicates that the onset for light absorption coincides with a critical packing density where monolayer structuring occurs and there is a sharp change in the effective dielectric constant of the film/water interface. Consistent with a featureless pressure–area isotherm for HPDR13, denoting no significant molecular rearrangement upon film compression, the UV–vis spectra did not vary with the surface pressure. The intensity of absorbed light increased, though, as the film was compressed owing to a higher density of chromophores. At higher subphase temperatures, larger flexibility of HPDR13 chains led to a more compact arrangement, causing the area per monomer to decrease and the absorbed light to increase—with approximately opposite trends.