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MULTIFLOW - An project overview

A large variety of industrially exploited complex soft matter fluid flows involve deformable interfaces between fluid phases and substrate-flow interactions. The presence of free boundaries and interfaces makes such flows inherently nonlinear and therefore subject to instabilities that trigger transitions to complex spatio-temporal behaviour. Quite frequently substrates are not smooth and do not have a simple geometry. In addition, the study of complex fluid flows encounters several other extremely challenging aspects and difficulties linked with the presence of hierarchies of widely varying nested time and length scales and the coupling of processes across these scales. In particular, processes on the nano-scale - involving phase transition and/or intermolecular forces, e.g. in the vicinity of a three-phase contact line - are not properly described within the framework of a self-consistent macroscopic formulation. Indeed, such processes are not only subject to irreversible couplings (such as non-equilibrium fluctuations) whose description is far from complete, but additional complications arise e.g. due to coupling with heat transfer and flow occurring in the vicinity of the interface (due to gravity, surface-tension gradients and action of surface forces). The objective of the network is to advance our fundamental understanding of complex fluid flows related to a number of emerging technologies. To do so it aims at bridging the gap between Applied and Industrial Mathematics, Chemistry, Physics and a number of Engineering disciplines. The objective shall be reached through the development and practical application of low-dimensional and/or coarse-grained models on and between different scales, i.e., models with reduced sets of variables and/or dimensions, and are capable to describe interdependent interfacial phenomena having disparate and largely different time and length scales. Theoreticl modelling will be accompanied by experimental work. In the following we list a selection of examples

Decomposition in and dewetting of films of binary mixtures

Experiments on the dynamics of thin films of binary mixtures of polymers show complex behaviour not known from the dewetting of simple liquids. The dewetting via convective flow caused by effective molecular interactions between substrate and film surface is accompanied by diffusion processes that may lead to phase ordering. These can even change the pathways of dewetting. In cases involving ultrathin films of thicknesses below 100 nm on or between chemically structured substrates the phase ordering (and dewetting) may be strongly influenced by the lateral variation of the substrate properties. In addition to confinement, the pattern formation can be driven by external forces. We plan to model the statics and dynamics of adsorbed thin films and droplets of binary mixtures on a solid substrate without and with the influence of evaporation of one of the components or an addtional solvent.

Chemocapillary and hydrochemical coupling / reactive contact line motion

Theoretical, computational and experimental study of the coupling between flow and structuring in problems involving reactions at interfaces between two liquids or (reactive) soluble and insoluble surfactants. Problems involve chemocapillary hydrochemical (solitonic) waves due to solutal Marangoni effects, instabilities caused by reaction-induced density stratification and interplay between mixing processes and topology.
Investigation of interplay between flow and chemical reactions / phase separation for free- surface systems involving moving contact lines (like drops) and/or porous support. Development of hybrid stochastic-deterministic micro-meso models for reactive contact lines.

Investigation of ultra-thin films dynamics

Development of hybrid micro-meso computational approaches (coupling discrete microscopic and continuum mesoscopic models via parameter passing, matching techniques) to model non-equilibrium fluctuations on nano-scales specifically in ultra-thin films and nano-drops. Novel methodologies are tested on simple liquids. Comparison to experiments.

Films of complex fluids and complex coupling effects

Investigation of the interfacial structure in films of liquids of varying viscosity, polymeric liquids and liquids containing surfactants or drag-reducing polymers. Effect of waves, phase change and complex rheology on interfacial mass transport and on heat transport through a (non-)porous wall. Influence of Marangoni and/or of Soret effects on wave patterns and transfer coefficients in falling films. Combination of chemical reaction and Marangoni effects.

Pattern formation in suspensions and solutions

Investigate the roles of hydrodynamics, evaporation, solvate diffusion, and interactions solvate/solvent with interfaces of different kinds. To develop protocols to tune the non-equilibrium self-organisation of such systems under evaporation. In particular, to exploit and control the interplay of phase transitions and dewetting/wetting in these systems with aim of generating well-defined structures.

Static and dynamic micro/macroscopic contact lines involving complex liquids

Experimental, theoretical and computational studies of moving contact lines for systems involving complex liquids (surfactants, micelles, adsorbed or reactive species, liquid crystals) that may qualitatively change their behaviour. Study of the influence of evaporation/condensation effects on contact line motion.

 
 
 
 
 

Last change:
ut 17.06.2011
u.thiele at lboro.ac.uk