Charged polymeric micelles as ion scavengers: experiments and self-consistent-field modelling

This thesis contains a study of micellization and micellar calcium binding efficiency of carboxy-modified Pluronic P85 triblock copolymers. These novel block copolymers are used as new antiscaling agents in a water treatment with a membrane separation process. Pluronic block copolymers are wellknown for their micellar thermoreversibility. Above certain temperature they aggregate to form micelles and below this temperature they disaggregate into unimers. The presence of weakly charged groups in the modified Pluronics makes the micellization becoming dependent on the ionic strength and pH. In total, the formation of micelles is a function of polymer concentration, temperature, ionic strength, and pH. A molecular model of a micelle in equilibrium is performed by using Scheutjens-Fleer self-consistent-field (SF-SCF) theory. From SF-SCF calculations, the trend in the micellization properties, such as aggregation number, critical micellization concentration (CMC), critical micellization temperature (CMT), and cloud point temperature (CPT), with varying governing variables are obtained.As antiscaling agents, novel block copolymers have to stabilize low-soluble salts in aqueous solutions. The precipitation of low-soluble salts (such as calcium and barium sulfate) onto reverse osmosis membranes are prevented by micelles composed of modified P85 block copolymers. This is made possible through the binding of cations with negatively charged groups in the micelles. To characterize the metal binding, several measurements (calorimetric, potentiometric and laser light scattering experiments) are combined with SF-SCF modelling. As a cation of interest, calcium is chosen for the whole study. Based on the experiments and SF-SCF modelling, the binding of calcium with micelles is driven by an electrostatic force as well as corresponding specific interaction. The electrostatic binding plays a major role in the overall micellar calcium binding. The micellization is shown to enhance the efficiency of calcium binding through a more effective electrostatic potential field.This thesis also focus on a micellization of weakly charged block copolymeric surfactants. The dependences of the micellization with pH and ionic strength lead to a variation in preferred micellar structures. An interesting coexistence of micelles with similar topology, namely crew-cut and starlike spherical micelles, at particular range of pH and ionic strength is addressed in this thesis. Furthermore, a non-spherical micellar structure is also considered in this thesis. The focus is on the bending properties of wormlike micelles as predicted by analyzing the curvature energy of toroidal micelles. The micelles are composed of either nonionic or weakly charged surfactants. The curvature energy of the wormlike micelles is accessible from the SCF modelling. The linear bending rigidity (or persistence length) is a strong function of the length of the hydrophobic chain. Moreover, the electrostatic persistence length of wormlike micelles has a strong resemblance with one belong to polyelectrolyte systems.