Multilayers of Low Charge Density Polyelectrolytes on Thin Films of Carboxymethylated and Cationic Cellulose

Multilayers with low charge density polyelectrolytes assembled on thin films of cellulose were studied by piezoelectric microgravimetry. The substrates were produced from colloidal suspensions of cotton fibers before and after modification with cationic and anionic groups via epoxy intermediates of quaternary ammonium and carboxymethylation, respectively. Two different levels of ionicity were used for each cellulosic substrate in order to investigate the role of the supporting surface in the buildup of the multilayer. It was found that while electrostatic interactions were leading factors in the assembly of high molecular weight, low charge density polyelectrolytes, other effects such as van der Waals and secondary cooperative forces played important roles. The charge properties of the substrate and the adsorbing polymer were relevant to the behavior of the self-assembled multilayers. Sequential additions of weak polyelectrolytes formed viscoelastic layers on all cellulose substrates. Adsorption of the first layer depended heavily on the charge characteristics of the substrate while the buildup of subsequent layers was mainly affected by the outermost adsorbed polymer. The polyelectrolyte multilayer formation with highest total adsorbed mass occurred on unmodified cellulose surfaces; therefore, in the case of the low charge density polyelectrolytes studied, substrate ionicity and functionalization may not be a requirement. Finally, the effect of anionic weak polyelectrolytes added after the first adsorbed polymer pair is highlighted in the context of reported observations for polyelectrolytes of high charge density. © Koninklijke Brill NV, Leiden, 2011