Self-Assembly and Spreading of Non-Ionic Trisiloxane Surfactants

Self-assembly and spreading of ordered structures on solid surfaces is a fundamentally interesting phenomenon, also potentially significant for applications. Here we report on the spreading behaviour of pure trisiloxane oligo(ethylene oxide) surfactants on high-and low-energy surfaces, which in terms of ordering represent two extremes. No specific structure appears as the surfactants spread over a high-energy surface. On low-energy surfaces, however, these surfactants self-assemble into well-defined bilayers. The area covered by the spreading film increases linearly with time, yielding apparent diffusion coefficients that are particularly sensitive to atmospheric humidity. The ability of the surfactant to form bilayers with dense interfacial packing of hydrophobic methyl groups, which enables their spreading over low-energy surfaces, is related to the chemical nature and the geometry of the molecules, while the sensitivity to atmospheric humidity is explained by specific water-ethylene oxide interactions. The conjunction of these properties could be the key feature explaining the "superspreading" properties of these ethoxylated trisiloxane surfactants.