Author: Yakov Lapitsky

Publisher:

Published: 2006

Total Pages:

ISBN-13: 9780542719486

Mixtures of oppositely charged surfactants and polyelectrolytes are of great interest to both industry and academia. Their applications range from household products to drug and gene delivery to the synthesis of novel materials. Their suitability for such a broad range of uses stems from their strong propensity to bind to one another where, depending on the strength and cooperativity of this adsorption process, surfactant/polyelectrolyte mixtures can have a broad range of useful physicochemical properties. This interplay between molecular-scale interactions and bulk properties makes the characterization of surfactant/polyelectrolyte binding a problem of great importance. Experimental determination of the binding isotherm is normally measured using a surfactant ion specific electrode method that requires time consuming experiments with sensitive, custom built equipment, which is not available in most laboratories. Thus, the first objective of this dissertation aims to develop a simple indirect method for approximating cooperative surfactant/polyelectrolyte binding isotherms using isothermal titration calorimetry (ITC). The Satake-Yang adsorption model is used to fit the binding constant (Ku), cooperativity parameter (u), and molar enthalpies of cooperative and non-cooperative surfactant adsorption to the ITC data. This approach is investigated using two surfactant/polyelectrolyte mixtures: sodium perfluorooctanoate (FC7) and N, N, N-trimethylammonium derivatized hydroxyethyl cellulose (UCARE [TM] Polymer JR-400), where the binding behavior is in good agreement with the Satake-Yang model, and dodecyltrimethylammonium bromide (DTAB) and poly(styrene sulfonate) (NaPSS), which deviates dramatically from model behavior. These case studies demonstrate that in order to apply the indirect ITC method of binding isotherm determination the surfactant/polyelectrolyte adsorption process must have no more than two dominant binding states. Thus, the technique works well for the FC7/JR-400 mixture but fails in the case of the DTAB/NaPSS adsorption (although its mode of failure in the case of DTAB/NaPSS offers insight into the multiple-binding-state adsorption mechanism of this non-model system). One typical macroscopic consequence of the abovementioned surfactant/polyelectrolyte binding is associative phase separation, wherein the concentrated phase is a viscous liquid, gel, or precipitate. The second objective of this dissertation exploits this phenomenon to form ordered gel phases that form particles (ranging from a few microns to a few millimeters in diameter), fibers, or planar sheets on a solid substrate. (Abstract shortened by UMI.).