Influence of pH on the Structure of Multilayer Films Composed of Strong and Weak Polyelectrolytes

Abstract

The sequential adsorption of oppositely charged polyelectrolytes called the "layer by layer" technique is a method for formation of ultrathin films with controlled thickness and interfacial properties. Composition of polyelectrolyte solutions, pH, and electrolyte concentration are important parameters governing formation of multilayer films. Since pH is the factor controlling charge of weak polyelectrolytes, the structure of multilayers should be sensitive to its value. In this paper we focused on formation of PE multilayer films composed from weak and strong polyelectrolytes. We used weak, branched polycation polyethyleneimine (PEI, 70 kDa) and strong polyanion poly-4-styrenesulfonate (PSS, 70 kDa) to form films by the layer-by-layer technique on the surface of silicon wafers under two deposition conditions: pH = 6 when PEI was strongly charged and pH = 10.5 when the charge density of PEI was low. Thicknesses of films were measured by single wavelength ellipsometry, and the results were confronted with ones concerning mass of the adsorbed films obtained by quartz crystal microbalance. We found that, depending on pH of the solutions, combination of weakly and strongly charged polyelectrolytes gave either linear or nonmonotonic increase of film thickness with a number of deposited PE layers. We observed a good correlation between multilayer film thickness and adsorbed mass. The atomic force microscopy images of surface topography of PEI/PSS films demonstrated large differences between films deposited at pH = 6 and 10.5. Additionally the cyclic voltamperometry was used to determine the differences in permeability of films formed at various pH conditions.

Formation and stability of poly-L-lysine/casein multilayers

“…For some conditions of the film formation one can also observe non-monotonous growth of its thickness with the number of deposited layer. This feature is characteristic for the formation of films consisting of weak polyelectrolytes (Elzbieciak et al 2009) and is caused by formation of surface polycation/polyanion complexes, which can be removed during next deposition step. One can notice that multilayers containing α-casein are much thicker than ones with β-casein, which can be explained by more flexible structure of α-casein (Horne 2002) and possibility of formation of larger aggregates.…”

Comparison of permeability of poly(allylamine hydrochloride)/and poly(diallyldimethylammonium chloride)/poly(4-styrenesulfonate) multilayer films: Linear vs. exponential growth

“…Many variables have strong influence on the buildup process of polyelectrolyte multilayers, like: solvent quality of polyelectrolytes [36], pH [37], temperature [31] and ionic strength [38,39]. Since the physico-chemical properties of multilayer films greatly depend on the conditions in which films grow, it is very important to understand how those parameters govern their structure.…”

Adhesion, proliferation, and gene expression profile of human umbilical vein endothelial cells cultured on bilayered polyelectrolyte coatings composed of glycosaminoglycans

“…1,2 These are fabricated through layer-by-layer deposition of high molecular weight polymers with opposing charges. 3,4 A particularly promising area for the therapeutic application of multilayered polyelectrolyte films is in the coating of drug-eluting coronary stents 5 as an attempt to prevent restenosis after percutaneous transluminal angioplasty. 6,7 For this purpose, it is essential that the stent coating must not only be biocompatible but should also be a surface that is conducive for the adhesion of endothelial cells so as to facilitate healing of the blood vessel and prevent restenosis and thrombosis.…”