Assembly, structural characterization, and thermal behavior of layer-by-layer deposited ultrathin films of poly(vinyl sulfate) and poly(allylamine)

Abstract

We have recently introduced a new method of creating homogeneous ultrathin films on solid supports, which is based on the electrostatic attraction between opposite charges. Consecutively alternating adsorption of anionic and cationic polyelectrolytes from their aqueous solution leads to the formation of multilayer assemblies. The multilayer buildup is easily monitored by small angle X-ray scattering (SAXS) and a linear increase of the film thickness with the number of adsorbed layers is observed. In the present study we concentrate on the polyelectrolytes poly(vinyl sulfate) (PVS) and poly(allylamine) (PAH), discussing especially the influence of the adsorption conditions of PVS on the growth and the properties of the resulting films. A stable film growth was found to depend on two prerequisites for the PVS deposition: an adsorption time of at least 15 min and a maximum concentration of added sodium chloride of 0.2 mol/L. In the regime of stable growth the multilayer film is able to smooth the surface roughness of the underlying glass substrate from 18 A to a value of 4.5 A. The addition of small amounts of electrolyte to the PVS solution leads to an increase of the thickness of one layer pair from 13 A (at 0.0 mol of NaCl/L) to 34 A (at 0.9 mol of NaCl/L). This behavior is similar to the well-known "rod-to-coü" transition of polyelectrolytes in solution and due to screening of electrostatic charges on the polymer chain. The films are stable up to temperatures of at least 160 °C but seem to lose trapped water above 60 °C.

Assembly, electrochemical characterisation and electrocatalytic ability of multilayer films based on [Fe(bpy)3]2+, and the Dawson heteropolyanion, [P2W18O62]6−

“…In previous multilayer systems, based on isopolyanions, it is known that the presence of protons in the adsorption solution significantly enhances the quantity of the anion that is reversibly adsorbed [16]. In addition to this when 0.5M Na 2 SO 4 is used as the electrolyte instead of 0.5M NaHSO 4 there is a lower amount of the anion adsorbed, proving it is indeed the presence of protons and not the ionic strength that causes this strong absorption between the anion and the electrode. It was found that the peak currents associated with the tungsten-oxo framework were in the range of 1.4 x 10 -6 to 2.0 x 10 -6 A when the solution from which the anion is adsorbed is aqueous 0.5M NaHSO 4, and only 2.5 x 10 -7 to 7.0 x 10 -7 A with poorer ill defined redox processes, when the solution is the more alkaline aqueous 0.5M Na 2 SO 4. , the peak currents increase in a step-wise fashion corresponding to the addition of one monolayer, namely 1.39 x 10 -11 mol cm -2 , which is typical of monolayer coverages for multilayer systems [20].…”

“…The technique of consecutive adsorption of anionic and cationic layers has been well documented by, for example, Decher et al [2][3][4] who reported on various systems involving these electrostatic interactions. Films with alternating layers of the anion cobalt phthalocyanine tetrasulphonate and cationic polydimethyldiallylammonium chloride prepared by electrostatic layer-by-layer adsorption were reported by Lvov et al [5].…”

“…The electrode was then soaked in HPLC grade water for five minutes. The coated electrode was next transferred to a 0.5M NaHSO 4 supporting electrolyte solution and a cyclic voltammogram recorded. This was followed by immersion of the electrode in an aqueous electrolyte free 0.5mM Fe(bpy) 3 2+ solution for 10 min.…”

Filmes poliméricos ultrafinos produzidos pela técnica de automontagem: preparação, propriedades e aplicações

“…Logo, Decher estendeu a técnica para camadas de polieletróli-tos 17 exclusivamente e filmes com várias camadas puderam ser obtidos da mesma maneira. Desde então, os mais diferentes materiais orgânicos vêm sendo depositados pelo método proposto por Decher.…”

“…5 eram bastante homogêneos e exibiam franjas de interferência periódicas, quando observados por espalhamento de raios X de baixo ângulo, revelando um ordenamento no filme em relação à sua direção normal, mais precisamente uma estrutura de camadas. Posteriormente, Decher e colaboradores estenderam o método para a deposição de polieletróli-tos 15,17 , inicialmente depositando camadas de poliânions alternadas com camadas de moléculas anfifílicas catiônicas, e camadas de policátions alternadas com camadas de moléculas anfifílicas aniônicas 15 . Novamente observaram que cada camada positiva após a deposição da camada de policátion, pode haver sítios com cargas negativas, sendo estes originários de segmentos de cadeias de poliânions que interpenetraram através do filme.…”