capillary wave study of linear and branched polysiloxanes at the air/water interface

The surface properties of two commercially available polysiloxanes, AK 1000 and AV 1000, have been examined at the air/water (A/W) interface in terms of the surface quasi‐elastic light scattering technique (SLS) in conjunction with surface pressure‐area ( II–A ) isotherm studies. Both are found to form stable, insoluble and promptly equilibrating monolayers at A/W. Being a mixture of linear poly(dimethylsiloxanes) (PDMS), AK 1000 is shown to follow the well established surface properties of PDMS. On the other hand, AV 1000, a mixture of linear and phenylsiloxane‐branched PDMS, referred to as PPMS, shows a different isotherm. The profiles of the surface dynamic viscoelastic parameters deduced from SLS, i.e., the surface dilational elasticity, ϵ d , and the corresponding viscosity, K , relative to the surface mass density, γ, are rather different. The magnitudes of ϵ d and K for both monolayers are comparable, while small but distinct differences are observed. In particular, in the high surface mass density region, the dynamic surface viscosity of PPMS films is about twice that of PDMS, but all values are still in the regime of very small viscosities ( K < 5×10 −8 kg/s). These findings are discussed in the context of the differences found in thermocapillary experiments between the two polymers.