Ion-Specific and Solvent Effects on PDADMA–PSS Complexation and Multilayer Formation

Jasmina Jukić,Karla Korade,Davor Kovačević,Ana-Marija Milisav,Ida Delač Marion

doi:10.3390/colloids5030038

Abstract

Among various parameters that influence the formation of polyelectrolyte complexes and multilayers, special emphasis should be placed on ion-specific and solvent effects. In our study, we systematically examined the above-mentioned effects on poly(diallyldimethylammonium chloride) (PDADMACl)-sodium poly(4-styrenesulfonate) (NaPSS) complexation in solution and at the surface by means of dynamic light scattering, ellipsometry and atomic force microscopy measurements. As solvents, we used water and water/ethanol mixture. The obtained results confirm the importance of ion-specific and solvent effects on complexes prepared in solution, as well as on multilayers built up on a silica surface. The experiments in mixed solvent solution showed that at a higher ethanol mole fraction, the decrease in monomer titrant to titrand ratio, at which the increase in the size of complexes is observed, takes place. The difference between chloride and bromide ions was more pronounced at a higher mole fraction of ethanol and in the case of positive complex formation, suggesting that the larger amount of bromide ions could be condensed to the polycation chain. These findings are in accordance with the results we obtained for polyelectrolyte multilayers and could be helpful for designing polyelectrolyte multilayers with tuned properties needed for various applications, primarily in the field of biomedicine.

Highlights

Research on polyelectrolytes has long been of interest to colloidal and polymer chemists, both from fundamental and applicational points of view
Research on polyelectrolyte complexes began as early as the 1930s, when Bungenberg de Jong et al [4] investigated the interactions between oppositely charged natural polyelectrolytes and noticed the formation of products known in the literature as polyelectrolyte complex coacervates [5]
The aim of this paper is to investigate ion-specific effects in two different solvents on the formation and properties of complexes and multilayers formed by interactions of two model polyelectrolytes: poly(diallyldimethylammonium chloride) (PDADMACl) and sodium poly(4-styrenesulfonate), (NaPSS)

Summary

Introduction

Research on polyelectrolytes has long been of interest to colloidal and polymer chemists, both from fundamental and applicational points of view. It is well known that just by mixing aqueous solutions of positively and negatively charged polyelectrolytes the products commonly known as polyelectrolyte complexes (PECs) or interpolyelectrolyte complexes are formed, predominantly due to the electrostatic attraction between the oppositely charged chains. Such reactions are usually considered to be entropically driven because of the rise in total entropy due to the release of counterions condensed to polyelectrolyte chains to the solution. Oppositely charged secondary complexes of larger size are being formed, usually followed by the coalescence of primary and secondary complexes, which is observed as macroscopic phase separation, named flocculation. The nanocomplex charge reversal was achieved in the high polyelectrolyte concentration regime by the abrupt instead of stepwise titrant addition

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