Polyelectrolytes: Theory, Properties and Applications

Book Preface

In this book, Chapter One discusses the structural properties and phase behavior of neutral and partially charged diblock copolymers in solution. Chapter Two presents a comprehensive study of the complex physico-chemistry associated with the adsorption of polyelectrolyte layers, both single layer or multilayers formed for oppositely charged polyelectrolytes, onto solid surface, paying special attention to the adsorption of polyelectrolytes onto charged surfaces. Chapter Three presents the complexation of the linear, inherently hydrophobic, anionic polyelectrolyte poly[sodium (sulfamate/carboxylate)isoprene] (SCPI) with the cationic surfactant dodecyltrimethylammonium bromide (DTMAB), studied mainly by light scattering methods.

Chapter 1 – Structural properties and phase behavior of neutral and partially charged diblock copolymers dispersed in solution are investigated using the random phase approximation with effective interactions taking into account the excluded volume and the long range electrostatic contributions. The mismatch of polymer/solvent solubility and inter block repulsion are analyzed to highlight the interplay between macro and microphase separation processes. For symmetrical diblock copolymers, composition and total concentration fluctuations are decoupled, the inter block incompatibility driven by ab is responsible for microphase transition whereas the polymer/solvent interaction drives the macrophase transition. The presence of charges on one block leads to polyelectrolyte effects and compatibility enhancement which are investigated in terms of the degree of ionization and ionic strength. The polyelectrolyte aspect together with the amphiphilic character and the impacting solvent quality lead to peculiar solution properties combining structural and phase behavior. The random phase approximation model is developed for a dispersed copolymer solutions while under the conditions of micelle formation, scaling approach is used to briefly discuss the critical micelle concentration and the aggregation number based on selected reports from the literature.

Chapter 2 – The adsorption of polyelectrolytes onto charged surfaces plays a central role in many technological areas, including: modification of adhesion and wetting, increase of lubrication and friction reduction. The careful control of the processes involved in the polyelectrolyte adsorption onto solid surfaces is essential for the development of applications in several fields: cosmetic, drug delivery, biomaterials and oil recovery. Therefore, the understanding of the different variables (e.g., ionic strength, pH, temperature, etc.) that modify the balance of interactions governing the adsorption of polyelectrolytes is a scientific challenge for both basic and applicative purposes. The aforementioned variables are mainly related to the modification of the charge density of both polymer and surface, playing a key role on the control of the different contributions involved in the formation of the layers: electrostatic, specific, entropic, etc. This Chapter presents a comprehensive study of the complex physico-chemistry associated with the adsorption of polyelectrolyte layers, both single layer or multilayers formed for oppositely charged polyelectrolytes, onto solid surface, paying special attention to the adsorption of polyelectrolytes onto charged surfaces.

Chapter 3 – The authors present the complexation of the linear, inherently hydrophobic, anionic polyelectrolyte poly[sodium (sulfamate/carboxylate)isoprene] (SCPI) with the cationic surfactant dodecyltrimethylammonium bromide (DTMAB), studied mainly by light scattering methods. At low surfactant concentrations the polyelectrolyte aggregates (already formed in surfactant-free solutions) shrink, whereas at higher surfactant concentrations secondary aggregation takes place leading to a strong increase in scattered intensity and a twofold increase in size. The charge of the aggregates decreases abruptly in the first complexation regime while more mildly in the second one as observed by ζ-potential measurements in electrophoretic light scattering. The resulting polyelectrolyte-surfactant complexes are fairly monodisperse (compared to the initial polyelectrolyte aggregates) and they contain well-defined hydrophobic domains (proof of complex coacervate phases) as shown by pyrene fluorescence probing. The system under study is proved to have tunable complexation properties not only by its dependence on surfactant content, but also by the effect of dilution upon already formed complexes, which shows a gradual decrease in the hydrophobic domains and a variation of the complexes size.