Study of the Microcharacter of Ultrastable Aqueous Foam Stabilized by a Kind of Flexible Connecting Bipolar-Headed Surfactant with Existence of Magnesium Ion

In this paper, ultrastable aqueous foam stabilized by a kind of flexible connecting bipolar-headed surfactant alkyl polyoxyethylene sulfate (AE₃S) with coexisting Mg²⁺ was reported. Detailed molecular behaviors of AE₃S in foam film with coexisting divalent cationic Ca²⁺ or Mg²⁺ were investigated by molecular dynamic simulation, comparing with the traditional surfactant sodium dodecyl sulfate (SDS), to find out how the microcharacter and array behavior of molecules in the foam film determined by molecular interaction effect the foam stability. It was found that the ultrastable foam film obtained by the cooperation of magnesium ions and AE₃S was driven from two aspects: one is the favorable arrangement of surfactant molecules, and the other is the increase of capacity of foam films for resolutely holding water molecules deduced by a dipolar pair formed by the flexible connecting head groups of AE₃S and hydrated Mg²⁺ via intermolecular coactions, both related to the presence of magnesium ions. Foam lamella stability measurement and foam decay method were both used to evaluate the stability of foam. Fourier transform infrared (FT-IR) was used to detect the composition variation of foam film in the drainage process; the vibration peak of OH for water molecule shifted from the 3390 cm^–1 (being assigned to the bulk water integrated by hydrogen bonds) to 3685 cm^–1 (being assigned to the vibration of isolated water molecules) for the ultrastable foam film after complete drainage, which agreed very well with the molecular simulation results