Surface Dilatational Rheology of Carboxyl-Containing Dimethylsiloxane Oligomers in Langmuir Films at the Air-Water Interface

The study of the viscoelastic properties of interphase layers, which can be modeled in Langmuir films, is of interest for estimating the stability during emulsification and stabilization of heterophase systems. Langmuir films of carboxyl-containing dimethylsiloxane oligomers were formed at the water-air interface and were comprehensively studied by measurement of surface pressure and surface potential isotherms and Brewster angle microscopy. The static elastic modulus was theoretically determined from surface pressure isotherms whereas dilatation storage and loss moduli were defined by the barrier oscillation method and plotted as amplitude sweeps and frequency dependences. For polymers distinguished by attachment of carboxyl groups to the dimethylsiloxane chain and molecular mass, the correlation between the viscoelastic behavior of the films and the conformation of macromolecules corresponding to surface pressure vs. area change was shown.