Wednesday, November 7, 2007 - 8:50 AM
355b

Understanding Superspreading: An Examination Of Aqueous Bulk And Interfacial Sturcture Of Nonionic Surfactant Mixtures

Makonnen M. Payne, Chemical Engineering, The City College of New York and The Graduate School and University Center of the City University of New York, Steinman Hall (T-305), 140th Street and Convent Avenue, New York, NY 10031, Alexander Couzis, Dept. of Chemical Engineering, City College of New York, 140 St and Convent Ave, New York, NY 10031, and Charles Maldarelli, Chemical Engineering Department and Benjamin Levich Institute, City College and the Graduate Center of the City University of New York, Steinman Hall, 140th St @ Convent Ave, New York, NY 10031.

The ability for some of the nonionic trisiloxane surfactants to completely and rapidly wet a hydrophobic surface has been well documented for several years. However, to date, the behavior of the trisiloxane surfactants at the solid-liquid interface is not yet completely understood, leading to an incomplete understanding of the mechanism for complete wetting. In this study, we use vibrational sum-frequency generation spectroscopy (VSFG) to gain insight to water's molecular organization on solid surfaces of various surface energies, ranging from the low surface energy octadecyltrichlorosilane monomer on quartz to a high surface energy neat quartz-water interface. In addition, we examine the behavior of water on those same surfaces when surfactant mixtures are added to the water. The surfactant mixtures used are synergistic combinations of 1-dodecanol with high purity linear nonionic poly(ethylene glycol) n-alkyl ether surfactant as well as the neat trisiloxanes. VSFG results demonstrate how the trisiloxane surfactants restructure the water at the water/hydrophobic solid interface to reduce the free energy, and this provides insight into superspreading. VSFG results also show synergistic mixtures of the ethoxylates and alcohols, which have superspreading capabilities, exhibit water restructuring similar to that of the trisiloxane surfactants. This result is also confirmed by the comparable physical and interfacial properties between the synergistic mixtures and the trisiloxanes, as determined by pendant bubble tensiometry, cross polarized microscopy, dynamic light scattering and cryo-TEM.