Static and Dynamic Light Scattering of Polyelectrolyte/ Surfactant Solutions: the Na-Hyaluronate/(C 10 TAB) System Marcos A. Villetti, 1,2 Redouane Borsali,* 3 Janaina S. Crespo, 1,4 Valdir Soldi, 1 Kazuhiro Fukada 5 1 POLIMAT–Universidade Federal de Santa Catarina, Departamento de Quimica, Florianopolis 88040-900, Santa Catarina, Brazil 2 Grupo de Cie ˆncias dos Materiais, Departamento de Fisica, Centro de Cie ˆncias Naturais e Exatas (CCNE), Universidade Federal de Santa Maria (UFSM), 97105-900 Santa Maria, RS, Brazil 3 LCPO-CNRS-ENSCPB- Bordeaux University (UMR 5629), 16 Avenue Pey-Berland, 33607 Pessac, France E-mail: borsali@enscpb.fr 4 Departamento de Fisica e Quimica, Universidade de Caxias do Sul, 95070-560 Caxias do Sul, RS, Brazil 5 Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Minamiohsawa 1-1, Hachiohji, Tokyo 192-0397, Japan Received: November 17, 2003; Revised: February 11, 2004; Accepted: February 16, 2004; DOI: 10.1002/macp.200300192 Keywords: dynamic light scattering; polyelectrolytes; sodium hyaluronate; static light scattering; surfactants Introduction The properties in aqueous polymer/surfactant complex solu- tions are an important and developing field of research, [1,2] both for the relevance of the interactions in biological systems and for technical applications. Avariety of methods are available to examine polymer-surfactant interac- tions including: fluorescence quenching techniques, [3–8] Summary: This work discusses the interactions between the anionic polyelectrolyte sodium hyaluronate (Na-Hy) and the cationic surfactant decyltrimethylammonium bromide (C 10 TAB). Static and dynamic light scattering experiments were carried out in the single homogenous phases (region I: [C 10 TAB] < 0.040 M and region III: [C 10 TAB] > 0.350 M) in ‘‘salt-free’’ and at different added salt concentrations (NaCl) in order to gain more understanding on the chain conforma- tion and on the dynamics of polyelectrolyte/surfactant sys- tems. In region I, the Na-Hy ‘‘salt-free’’ system exhibits the expected polyelectrolyte properties, i.e. the scattering inten- sity increases with the addition of surfactant or salt. As a consequence of this screening of the electrostatic interac- tions, a decrease in both the radius of gyration R g and the second virial coefficient A 2 is observed. This decrease is found more pronounced in the presence of surfactant C 10 TAB than in the case of added salt (Na-Hy/NaCl). Consequently, the calculated apparent persistence length L t , assuming a worm- like chain at high ionic strength, is found about 58 A ˚ in the case of surfactant and L t ¼ 71 A ˚ 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 C 10 TAB > 0.040 M. As far as the dynamic properties are concerned, the autocorrelation functions in ‘‘salt-free’’ solu- tions measured in region I are better described by two relax- ation 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 C 10 TAB surfac- tant and NaCl salt. Macromol. Chem. Phys. 2004, 205, 907–917 DOI: 10.1002/macp.200300192 ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper 907