Pressure Changes Across a Membrane Formed by Coacervation of Oppositely Charged Polymer-Surfactant Systems.

We investigate the mass transfer and membrane growth processes during capsule formation by the interaction of the biopolymer xanthan gum with CTAB surfactants. When a drop of xanthan gum polymer solution is added to the surfactant solution, a membrane is formed by coacervation. It encapsulates the polymer drop in the surfactant solution.

Neutron radiography of an anisotropic drainage flow.

Liquid drainage through foam is dominated by gravity, capillary, and viscous forces. The liquid is conducted by an isotropic network of Plateau borders; however, imposed stress changes the alignment of the foam's structural elements. Previous numerical simulations predicted that a vertical drainage flow will be deflected horizontally if the foam is sheared.

The impact of an ultrasonic standing wave on the sorption behavior of proteins: Investigation of the role of acoustically induced non-spherical bubble oscillations.

Hypothesis: Protein molecules adsorb on the air/liquid interface due to possessing a hydrophobic side. A full surface coverage is important in many processes such as in protein harvesting by foam fractionation. The adsorption of proteins in low concentration solutions is preceded by a relatively long time lag known as the induction period.

Foam fractionation Tags (F-Tags) enabling surfactant-free, activity-preserving recovery of enzymes.

Enzymes have become important tools in many industries. However, the full exploitation of their potential is currently limited by a lack of efficient and cost-effective methods for enzyme purification from microbial production. One technology that could solve this problem is foam fractionation.

Neutron radiography of liquid foam structure near a vertical wall.

At a solid boundary, the structural formation of bubbles is different from that in the bulk of a liquid foam. The presence of a solid boundary imposes additional constraints, resulting in a crystalline arrangement of the bubbles. For dry and monodisperse foam, the Kelvin and Fejes-Tóth structure is expected in the vicinity of the wall, while a random ordering should occur in the bulk.

Rsn-2-mediated directed foam enrichment of β-lactamase.

Today, the availability of methods for the activity-preserving and cost-efficient downstream processing of enzymes forms a major bottleneck to the use of these valuable tools in technical processes. A promising technology appears to be foam fractionation, which utilizes the adsorption of proteins at a gas-liquid interface. However, the employment of surfactants and the dependency of the applicability on individual properties of the target molecules are considerable drawbacks.

Investigating Pore-Opening of Hydrogel Foams at the Scale of Freestanding Thin Films.

Controlling the pore connectivity of polymer foams is key for most of their applications, ranging from liquid uptake, mechanics, and acoustic/thermal insulation to tissue engineering. Despite their importance, the scientific phenomena governing the pore-opening processes remain poorly understood, requiring tedious trial-and-error procedures for property optimization. This lack of understanding is partly explained by the high complexity of the different interrelated, multiscale processes which take place as the foam transforms from an initially fluid foam into a solid foam.

Interfacial Behavior of Particle-Laden Bubbles under Asymmetric Shear Flow.

The behavior of moving bubbles has mostly been studied in an axisymmetric flow field. To extend the knowledge to practical conditions, we investigate the interfacial and hydrodynamic properties of bubbles under asymmetric shear forces. Experiments are performed with a buoyant bubble at the tip of a capillary placed in a defined shear flow in the presence of surfactants, nanoparticles, and glass beads.

Interfacial flow of a surfactant-laden interface under asymmetric shear flow.

Hypothesis: The shear stress of the axisymmetric flow field triggers a nonuniform distribution of the surfactants at the surface of a rising bubble, known as stagnant cap. The formation of the stagnant cap gives rise to Marangoni stresses that reduce the mobility of the interface, which in return reduces the rising velocity. However, the conditions in technological processes usually deviate from the linear rise of a single bubble in a quiescent unbounded liquid.

X-ray particle tracking velocimetry in liquid foam flow.

In this work, we introduce a novel approach to measure the flow velocity of liquid foam by tracking custom-tailored 3D-printed tracers in X-ray radiography. In contrast to optical observations of foam flow in flat cells, the measurement depth equals 100 mm in the X-ray beam direction. Light-weight tracers of millimetric size and tetrapod-inspired shape are additively manufactured from stainless steel powder by selective laser melting.

Ultrasonic measurements of the bulk flow field in foams.

The flow field of moving foams is relevant for basic research and for the optimization of industrial processes such as froth flotation. However, no adequate measurement technique exists for the local velocity distribution inside the foam bulk. We have investigated the ultrasound Doppler velocimetry (UDV), providing the first two-dimensional, non-invasive velocity measurement technique with an adequate spatial (10mm) and temporal resolution (2.

A simple collision model for small bubbles.

In this work, a model for the interaction force between a small bubble and a wall or another bubble is presented. The formulation is especially designed for Lagrangian calculations of bubble or soft sphere trajectories, with or without resolution of the continuous fluid. The force only relies on position and velocity of the bubble.

Creating Honeycomb Structures in Porous Polymers by Osmotic Transport.

Understanding why honeycombs are shaped the way they are has moved biologists, physicists, chemists, and mathematicians alike. It was only recently that the honeycombs' shape "at birth" was included in the ongoing discussions: at birth, the cells are spherical but then transform into the well-known hexagons. It was proposed that a flow of wax-driven by surface tension effects-is the reason for this transformation.