Thermal and Mechanical Properties of Dried Foam Films and Their Incorporation of Water-Soluble Compounds

Abstract

Dried foam films (DFFs), which are free-standing reversed bilayers covering the holes of micrometers, are obtained by using several types of surfactants. In this article, we examined the formation of DFFs from a wide range of surfactants, systematically changing the headgroup, the counterion, the length and number of alkyl chains, and so forth. Some DFFs showed thermal stability higher than 150 °C. The interaction among headgroups in each monolayer of DFFs significantly contributed to the high thermal stability. The elastic moduli of DFFs were in the range of 4−42 MPa, as determined by a nanoindentation technique using AFM. A nonionic surfactant (Brij-35) formed stable DFFs only when urea was incorporated to form hydrogen bonds with the ethylene oxide units. The thermal stability of DPC (dodecylphosphocholine) films was increased up to 220 °C by adding Cd²⁺ because of the formation of a coordination network with the phosphate groups. Then the elastic modulus increased from 15 to 32 MPa. It was also possible to incorporate polyelectrolytes (Na₂SiO₃ and PAH) and a cadmium polynuclear complex ([Cd₁₀(SCH₂CH₂OH)₁₆]·(ClO₄)₄) into the interlayer space of DFFs by tuning the proximal electrostatic interaction with the headgroups of surfactants.