Arrested segregative phase separation in capillary tubes

Continuous flow structuring of anisotropic biopolymer particles

We review concepts and provide examples for the controlled structuring of biopolymer particles in hydrodynamic flow fields. The structuring concepts are grouped by the physical mechanisms governing drop deformation and shaping: (i) capillary structuring, (ii) shear and elongational structuring and (iii) confined flow methods. Non-spherical drops can be permanently structured if a solidification process, such as gelation or glass formation in the bulk or at the interface, is superimposed to the flow field. The physical and engineering properties of these processes critically depend on an elaborate balance between capillary phenomena, rheology, gel or glass formation kinetics, and bulk heat, mass and momentum transfer in multiphase fluids. This overview is motivated by the potential of non-spherical suspension particles, in particular those formed from 'natural' and 'sustainable' biopolymers, as rheology modifiers in food materials, consumer products, cosmetics or pharmaceuticals.

Capillary adhesion in the limit of saturation: thermodynamics, self-consistent field modeling and experiment

We introduce a simple thermodynamic argument for capillary adhesion forces, for various geometries, in the limit of saturation of the bulk phase. For one specific geometry (i.e., the sphere-plate geometry such as that found in the colloidal probe AFM technique), we provide evidence of the validity of our model by comparison with experiment and self-consistent field calculations. With this latter numerical technique, we also discuss deviations from the macroscopic argument both when the system is moved away from saturation and when the capillary bridge becomes so small that macroscopic thermodynamics is no longer accurate.

Equilibrium capillary forces with atomic force microscopy

We present measurements of equilibrium forces resulting from capillary condensation. The results give access to the ultralow interfacial tensions between the capillary bridge and the coexisting bulk phase. We demonstrate this with solutions of associative polymers and an aqueous mixture of gelatin and dextran, with interfacial tensions around 10 microN/m. The equilibrium nature of the capillary forces is attributed to the combination of a low interfacial tension and a microscopic confinement geometry, based on nucleation and growth arguments.