Regensburg 2025 – scientific programme

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BP: Fachverband Biologische Physik

BP 12: Biomaterials, Biopolymers and Bioinspired Functional Materials III (joint session CPP/BP)

BP 12.5: Talk

Tuesday, March 18, 2025, 10:45–11:00, H46

Proteins as foam stabilizers: From single foam lamellas to macroscopic foams — •Kevin Gräff, Sebastian Stock, Luca Mirau, Matthias Kühnhammer, Olaf Soltwedel, and Regine von Klitzing — Terchnische Universität Darmstadt, Darmstadt, Germany

Foams consist of foam lamellas, which separate single air bubbles from each other. Investigation of lamellas is crucial to understand foam properties. In order to untangle electrostatic, steric and network stabilization effects, we compare two globular proteins (β-lactoglobulin and Lupine Protein Isolate) and a disordered, flexible protein (whole casein) at different pH values. The Thin Film Pressure Balance (TFPB) device based on image intensity measurements generates spatially resolved disjoining pressure isotherms. We introduce feature tracking for the measurement of interfacial mobility and stiffness of lamellas as a novel method. Around the isoelectric point, Newton Black Films (NBFs) form, which are stable for the globular proteins while they are unstable for the disordered flexible one. This difference in film stability is explained by different characteristics of network structures in the lamellas from the respective protein solutions. Small-Angle Neutron Scattering (SANS) evaluation with a new model for foams proves the presence of NBFs within macroscopic foams. For a complete picture we compare the TFPB findings with X-ray reflectometry as well as with Brewster Angle Microscopy on single interfaces.

[1] Gräff, K. et al, (2022), Untangling effects of proteins as stabilizers for foam films, Front. Soft. Matter 2:1035377.

Keywords: Protein Foams; Foam Lamellas; Thin Film Pressure Balance; Disjoining Pressure; Small Angle Neutron Scattering