Berlin 2005 – scientific programme

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CPP: Chemische Physik und Polymerphysik

CPP 5: SYMPOSIUM: Dynamics of multi-component fluids POSTER

CPP 5.24: Poster

Friday, March 4, 2005, 17:15–19:00, Poster TU D

THE MOLECULAR ORIGIN OF FOAM STABILITY: A VIBRATIONAL SURFACE SUM FREQUENCY STUDY OF THE INTERFACIAL WATER — •Patrick Koelsch and Hubert Motschmann — Max-Planck-Institute of Colloids and Interfaces, Am Muehlenberg, 14476 Potsdam, Germany

Foam formation and foam stability must be clearly distinguished. While foam formation could successfully be linked to the relative dynamic surface pressure, it turned out to be impossible to establish a similar relation between foam stability and a fundamental system parameter.

A novel measurement technique developed at the MPI-KGF allows precise measurement of the complex surface dilatational modulus in a broad frequency range. These measurements clearly relate the intrinsic surface dilatational viscosity to the stability of a foam lamella. The intrinsic surface viscosity damps film deformation prior to bubble rupture.

However, what is the molecular process which dissipates the energy? To study this, we performed Infrared Visible Sum Frequency Generation Spectra of two surfactant systems, one forming stable foam lamellas and the other not. The surface tension and magnitude of the elasticity modulus is comparable in both cases. IR-VIS SFG spectrum records the vibronic signature of the surface layer with a high surface specificity. The interfacial water structure shows in both cases striking differences. A molecular picture of the dissipative process is derived.