Characterization of aggregates formed by hydrophobically modified cationic dextran and sodium alkyl sulfates in salt-free aqueous solutions.
The interaction between polyelectrolytes based on dextran with pendant N-alkyl-N,N-dimethyl-N-(2-hydroxypropyl) ammonium chloride groups, where n = 2, 4, 8, 12, or 16, and sodium alkyl sulfates, SCnS, with n = 8, 10, 12, 14, and 16, has been studied by conductometry and fluorescence techniques. Comparison of cumulative specific conductivities of the mixtures of polymer-surfactant over a large surfactant concentration range, with those of pure surfactant and NaCl, has clearly shown that the surfactants start to bind to polymer at very low concentrations (10(-6) M), forming mixed aggregates. The steady-state emission fluorescence measured in the presence of pyrene, 1,3,6-diphenylhexatriene (DPH), and 1-pyrenylbutyric acid sodium salt demonstrated the existence of a critical surfactant concentration (CACs) at which the previously formed mixed aggregates are interconnected due to self-association of surfactant molecules included in different mixed polymer/surfactant aggregates. Above CACs, the mixed aggregates change dramatically their properties (hydrophobicity, size, DPH solubilization) which depend on both polymer and surfactant hydrophobicities and concentrations. The characterization of the new formed aggregates at different surfactant concentration ranges is derived mainly from their ability to solubilize hydrophobic compounds. The variety of fluorescence techniques used, combined with conductometric measurements and previous calorimetric information allowed us to provide here a comprehensive study and new interpretation of the solution behavior of these polymer-surfactant systems.
Petru Poni Institute of Macromolecular Chemistry, 700487 Iasi, Romania. nichifor@icmpp.ro
Marieta
M
Nichifor
Margarida
M
Bastos
Sonia
S
Lopes
Antonio
A
Lopes