Synergistic Surfactant Interactions and the Consequences on Phase Behavior, Interfacial Tension Reduction and Hydrophobic Surface Wetting

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 work we report our findings with regard to the synergistic interactions between polyethylene oxide surfactants of the general structure CiE j and compare the behavior to a known super wetting surfactant. Pendant drop tensiometry experiments and sessile drop contact angle measurements on hydrophobic surfaces were conducted on combinations of CiE j surfactants with 1-dodecanol. We found that a number of combinations were capable of reducing significantly the air-liquid tension, however only systems that exhibited the propensity to form extended liquid crystalline phases, as shown by the combination of cross-polarized microscopy, cryo-TEM, and light scattering experiments, were able to improve on the wetting performance of the these systems. We have also conducted the parallel experiment focused on the surfactant adsorption at the hydrophobic solid-liquid interface. Using in-situ infrared internal reflection spectroscopy and complimentary sum-frequency generation spectroscopy, we are able to dynamically interrogate the surfactant adsorption kinetics and interfacial water structure evolution at the hydrophobic solid-liquid interface. We will relate these findings to gain insight into the molecular requirements for superspreading