(274e) Interfacial Properties of Self-Assembled Polymer/Surfactant Mixed Nanoparticles

Interfacial behavior of novel nanoparticle systems have been the focus of recent research efforts in colloid science due to their applications in consumer products, petroleum engineering and biotechnology.  We will discuss the surface adsorption and surface rheological properties of self-assembled polyelectrolyte-surfactant aggregates (with radii 50-200 nm). Using the Wilhelmy plate method, we find that  these nanoparticles are more surface active than the surfactant or the polyelectrolyte can lower the critical micelle concentration of the surfactant alone by a factor of 6. What is even more surprising is that these nanoparticles  show a concentration dependent two-stage adsorption to the air/water interface. We propose that these nanoparticles undergo hydrophobic interface induced "disintegration", which is dominated by the concentration of nanoparticles, and the concentration of the entrapped surfactant at the interface. Further evidence of this interface-inducced release is provided by a sharp change in surface viscosity at times corresponding to the "disintegration" or release of entrapped surfactant. Three orders of magnitude increase in the sensitivity of our recently developed nanorod interfacial rheometer allows us to detect this change in the surface viscosity during the rearrangement of the nanoparticles at the interface.