arXiv subjects

Kevin Gräff

Publications and source records attributed to Kevin Gräff.

2 recordsLinked to original sources

arXiv2026

A Multi-scale Investigation of Aqueous Foams Stabilised by PNIPAM Microgels

Aqueous foams possess multiple structural motifs across different length scales: macroscopic foam, bubbles, foam films and the air/water interface. In this study, macroscopic foams are generated by sparging gas through an aqueous dispersion of PNIPAM microgels which act as foam stabilisers due to their surface activity. The stiffness of the microgels and thus their interfacial activity are tuned by variation of the cross-linker density. The effect of the cross-linker density and the microgel concentration on the resulting foam formation properties (foamability) and the foam stability are investigated. A lower cross-linker density and a higher microgel concentration enhance the foamability, generate foams with smaller bubbles and higher liquid fractions, and increase the foam stability. These observations are correlated with the microgel behavior at the single air/water interface examined by pendant drop tensiometry and Langmuir compression experiments as well as the mobility in single free-standing foam films determined using a Thin Film Pressure Balance. Our findings highlight good agreement across all length scales: increased foamability correlates with a faster decrease in surface tension, and higher foam stability with a higher surface elastic modulus of a microgel-covered single air/water interface and decreasing mobility in foam films.

cond-mat.soft↗

arXiv2024

Drying of Soft Colloidal Films

Thin films made of deformable micro- and nano-units, such as biological membranes, polymer interfaces, and particle-laden liquid surfaces, exhibit a complex behavior during drying, with consequences for various applications like wound healing, coating technologies, and additive manufacturing. Studying the drying dynamics and structural changes of soft colloidal films thus holds the potential to yield valuable insights to achieve improvements for applications. In this study, we employ interfacial monolayers of core-shell microgels with varying degrees of softness as model systems and investigate their drying behavior on differently modified solid substrates (hydrophobic vs. hydrophilic). By leveraging on video microscopy, particle tracking, and thin film interference, we shed light on the interplay between microgel adhesion to solid surfaces and the immersion capillary forces that arise in the thin liquid film. We discovered that a dried replica of the interfacial microstructure can be more accurately achieved on a hydrophobic substrate relative to a hydrophilic one, particularly when employing softer colloids as opposed to harder counterparts. These observations are qualitatively supported by experiments with a thin film pressure balance which allows mimicking and controlling the drying process and by computer simulations with coarse-grained models.

cond-mat.soft↗