title: In situ UV-vis absorbance measurements for Langmuir films of poly[4'-[[2-(methacryloyloxy)-ethyl]ethylamino]-2-chloro-4-nitroazobenzene] (HPDR13) azopolymer.
abstract: 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.
authors.affiliation: Instituto de Física de São Carlos, Caixa Postal 369, 13560-970 São Carlos, São Paulo, Brazil.
authors.forename: D S
authors.initials: DS
authors.lastname: Dos Santos
authors.forename: F J
authors.initials: FJ
authors.lastname: Pavinatto
authors.forename: D T
authors.initials: DT
authors.lastname: Balogh
authors.forename: L
authors.initials: L
authors.lastname: Misoguti
authors.forename: O N
authors.initials: ON
authors.lastname: Oliveira
authors.forename: C R
authors.initials: CR
authors.lastname: Mendonça