Speakers
Description
Foams appear in many applications such as in personal care products, firefighting and food technology. An elegant tool to tune the foam stability is the addition of polymers of different charge, amphiphilicity or molecular architecture. An example, which will be addressed here are foams which are stabilized by stimuli-responsive microgels.
For understanding macroscopic foam properties, it is important to get deeper insight into the different length scales, i.e. the structuring of microgels at the air/water interface, in foam films, which separate the air bubbles from each other and (macroscopic) foams.
The presentation will focus on microgels based on Poly-N-isopropylacrylamid (PNIPAM). Their stiffness and deformation at the air/liquid interface are controlled by the amount of cross-linker content, which dominates the lateral pattern formation at the liquid interface. A challenge for studies of microgel-stabilized foam films is their massive inhomogeneities, which make it difficult to measure the respective foam film thickness. To get insight into foam film properties, we use a camera-based thin film pressure balance to study microgel-stabilized foam films in terms of disjoining pressure inside the foam films, drainage kinetics, and foam film stability [1, 2]. Film thickness profiles give insights into particle bridging, agglomeration and network formation in the foam films. A correlation is shown with the mechanical properties of the microgels as determined by atomic force microscopy (AFM) nanoindentation measurements. For a complete picture, small angle neutron scattering (SANS) measurements on macroscopic foams provide additional insights into the link between foams and single foam films [1, 3, 4].
References
[1] M. Kühnhammer, K. Gräff, E. Loran, O. Soltwedel, O. Löhmann, H. Frielinghaus, R. von Klitzing, Soft Matter, 18, 9249 - 9262, 2022, DOI: 10.1039/D2SM01021F
[2] https://download.hrz.tu-darmstadt.de/media/FB05/SMaI/V0011_Microgel_Foam_Films_KG_v2.mp4
[3] M. Kühnhammer, L. Braun, M. Ludwig, O. Soltwedel, L. Chiappisi, R. von Klitzing, Journal of Applied Crystallography, 55, 758, 2022, DOI: 10.1107/S1600576722004691
[4] M. Kühnhammer, T. Widmann, L. P. Kreuzer, A. J. Schmid, L. Wiehemeier, H. Frielinghaus, S. Jaksch, T. Bögershausen, P. Barron, H. Schneider, A. Hiess, P. Müller-Buschbaum, T. Hellweg, R. von Klitzing*, O. Löhmann. Applied Sciences, 11, 5116-5128, 2021. DOI: 10.3390/app11115116
