Static and Dynamic Light Scattering of Polyelectrolyte/Surfactant Solutions: the Na‐Hyaluronate/(C10TAB) System

Abstract

AbstractSummary: This work discusses the interactions between the anionic polyelectrolyte sodium hyaluronate (Na‐Hy) and the cationic surfactant decyltrimethylammonium bromide (C10TAB). Static and dynamic light scattering experiments were carried out in the single homogenous phases (region I: [C10TAB] < 0.040 M and region III: [C10TAB] > 0.350 M) in “salt‐free” and at different added salt concentrations (NaCl) in order to gain more understanding on the chain conformation and on the dynamics of polyelectrolyte/surfactant systems. In region I, the Na‐Hy “salt‐free” system exhibits the expected polyelectrolyte properties, i.e. the scattering intensity increases with the addition of surfactant or salt. As a consequence of this screening of the electrostatic interactions, a decrease in both the radius of gyration Rg and the second virial coefficient A2 is observed. This decrease is found more pronounced in the presence of surfactant C10TAB than in the case of added salt (Na‐Hy/NaCl). Consequently, the calculated apparent persistence length Lt, assuming a worm‐like chain at high ionic strength, is found about 58 Å in the case of surfactant and Lt = 71 Å in the case of added salt. This result demonstrates clearly that the binding of the surfactant to Na‐Hy is stronger than in the case of added salt and is at the origin of the phase separation that occurs at the concentration of C10TAB > 0.040 M. As far as the dynamic properties are concerned, the autocorrelation functions in “salt‐free” solutions measured in region I are better described by two relaxation modes (intermediate and slow) and by three relaxation modes (fast, intermediate and slow) in region III. The three relaxation modes reflect respectively the dynamics of free micelles (fast mode), association‐dissociation equilibrium of micelle‐like clusters (intermediate mode) and polymer‐micelles adsorption (slow mode). At high ionic strength (added salt) in region III, the micelle diameter increases (fast mode), the intermediate mode disappears and the polymer‐micelles adsorption diffusion coefficient increases due to the screening of the electrostatic interactions.Phase diagram of Na‐Hy polyelectrolyte in C10TAB surfactant and NaCl salt.imagePhase diagram of Na‐Hy polyelectrolyte in C10TAB surfactant and NaCl salt.