Adsorption polyelectrolyte onto metal

Ellipsometric Study of Adsorption of Polyelectrolyte onto a Metal Surface... 

For homopolyelectrolyte, we first studied the ellipsometric measurement of the adsorption of sodium poly(acrylate) onto a platinum plate as a function of added sodium bromide concentration (5). We measured the effect of electrolyte on the thickness of the adsorbed layer and the adsorbances of the polyelectrolyte. It was assumed that the Donnan equilibrium existed between the adsorbed layer and the bulk phase. The thickness was larger and the adsorbance of the polyelectrolyte was lower for the lower salt concentration. However, the data on the molecular weight dependence of both the adsorbance and the thickness of the adsorbed polyelectrolyte have been lacking compared with the studies of adsorption of nonionic polymers onto metal surfaces (6-9). 

Fig. 13.3 Schematic representation of capsules prepared by LbL adsorption of oppositely charged polyelectrolytes onto spherical charged spheres, followed by dissolution of sacrificial templates. During LbL coating, various charged elements (such as metal, magnetic or fluorescent nanoparticles) can be incorporated within the multilayers to add functionahty to the capsules. Reproduced from [40] with permission from Elsevier...

As mentioned above, all metal surfaces used in these studies contain an oxidic layer and non-specifically adsorbed surface contaminations. Even the copper surface contains an oxidic layer in the order of 1-2 nm thickness. The differences in the adsorption capacities of a metal and its corresponding metal oxide towards PVFA-co-PVAm were compared by means of Zn and ZnO as well as Fe and Fe2C>3. XPS was employed in order to determine the amount of the polyelectrolyte adsorbed onto the metal or metal oxide surface. XPS is a well established surface sensitive spectroscopic method with an information depth not higher than 10 nm. 

In soils and clays the most generally present biopolymers that naturally occur in the adsorbed state on mineral and clay particles are humic substances , or humic acids these are decomposition products of lignin, whidi is the major non-cellulosic polymer in wood and other plant debris. Humic acids (also called allomelanins (Merck Index, 1989)) are for the greater part polyphenolic compounds, usueJly anionic polyelectrolytes, which can complex metal ions, and are surface active and thus capable, upon adsorption onto mineral particles, to enhance their suspension stability in aqueous media (Chheda and Grasso, 1994). 

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