UV/Vis Spectroscopic Monitoring of Polyelectrolyte Adsorption onto Monolayers of Azobenzene Amphiphiles

Abstract

The complexation of an azobenzene-containing carboxylic acid amphiphile with a cationic poly(pphenylene) polyelectrolyte at the air/water interface results in changes of the monolayer structure. Compared to the monolayer of the amphiphile on pure water, a more expanded liquidlike structure can be suggested for the complex monolayer according to the increased area per amphiphilic molecule and Brewster angle microscopy. Furthermore, aggregation of the azobenzene moieties is suppressed in the complex. The differences in the spectral properties of the pure amphiphile monolayer and the polyelectrolyte complex monolayer due to their different structural order can be employed for investigation of the adsorption process: The adsorption of the polyelectrolyte to an already compressed amphiphile monolayer results in structural rearrangements and can, therefore, be monitored in situ as a change in the monolayer UV/vis spectra.

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

“…This is consistent with a featureless pressure-area isotherm, indicating the lack of significant molecular rearrangement upon film compression. Similar results were obtained for azodye monolayers complexed with polyelectrolytes [10,11] or in the case of amphiphilic azodyes [12,13].…”

Adsorption of anionic polyelectrolytes to dioctadecyldimethylammonium bromide monolayers

“…The adsorption of polyelectrolytes to such model surfaces results in changes of the monolayer structure and properties like area per amphiphile or monolayer morphology, which can be monitored by several methods [5][6][7]. If the amphiphile contains azobenzene chromophores, the adsorption may result in spectroscopic changes, too [8]. Monitoring the changes upon adsorption of a polyelectrolyte from a solution brought into contact with the preformed amphiphile monolayer, should allow to obtain information about the dynamic of the adsorption process.…”

“…Examples are: the change in the surface pressure (at constant area) [14,15,[17][18][19], changes in UV/vis spectra [8], and changes in the reflectivity at the Brewster angle [13,20].…”

Piezochromic Effect and Orientational Order in Monolayers and LB Multilayers of Poly(p-phenylenesulfonate)− Dioctadecyldimethylammonium Bromide Complexes

“…The structural changes occurring upon polyelectrolyte adsorption can be used to monitor the adsorption process when a preformed monolayer of ionic amphiphiles is brought into contact with a subphase containing an oppositely charged polyelectrolyte. [14][15][16][17][18] The properties of poly(p-phenylene)s may be applicable for advances in light-emitting diodes. Oriented films of poly(p-phenylene)s are of particular interest in this respect, because of their polarized emission.…”