EFFECT OF LINEAR CHARGE DENSITY IN THE COMPLEXATION OF OPPOSITELY CHARGED POLYMER/SURFACTANT SYSTEMS WITH FLUORESCENCE PROBES

L. CID; B. GINZBERG; M.C. MARCHI; S.A. BILMES

Fortaleza

Simposio; 15th Surfactants in Solution Symposium; 2004

15th Surfactants in Solution Symposium

Oppositely charged aqueous solutions of polyelectrolyte and surfactant are receiving great attention because of their industrial applications in areas like pharmaceutical, personal care, foods and also by the interest in the knowledge of the intermolecular interactions and hydrophobic aggregation phenomena. Amphiphiles systems like surfactants tend to self-assemble at a critical micelle concentration (cmc) but the addition of a polyelectrolyte in the solution was found to lower largely this value to a critical aggregation concentration (cac). After the cac the micellization of polymer bound surfactant occurs, forming polymer-surfactant complexes. At very low surfactant concentration the head groups of the surfactant individually bind to the charged groups on the polymer chains due to electrostatic attraction. The aggregates start to form at cac, whose value  is affected by the polyelectrolyte linear charge density and its rigidity. Fluorescence spectroscopy is widely used for the investigation of microscopic environments. Because the fluorescence properties of a fluorophore are quite sensitive to the microenvironment around the probe, valuable information can be extracted from the changes of a photophysical property of the probes upon progressive modification of a solution. The measured changes can then be used to infer changes in the immediate probe environment. In this work we present the study of aqueous solution of two polyelectrolytes: PAMPS (polyacrylamide sulfonate), with 10% and 25% of charge density, and a cationic surfactant, dodecyltrimethylammonium bromide (DTAB). We have investigated the interactions between each polyelectrolyte and DTAB at different  and increasing concentrations. Two fluorescence probes: pyrene and prodan have been used to detect and  characterise the polymer/surfactant aggregates. We found that  the cac for PAMPS 10% is higher than for PAMPS 25% and the   aggregates PAMPS 25%/DTAB are significantly more hydrophobic.