Here - Institute for Building Materials - ETH Zürich

Interfacial rheology and particle laden interfacesJan VermantDepartment of Chemical Engineering,K.U. Leuven, BelgiumSeveral high interface systems, such as foams or emulsions, derive their functionfrom the fact that surface active molecules and particles collect at fluid interfaces andrender them non-linear in their response to flow and deformation. When this occurs,the interfaces acquire a complex microstructure that must be interrogated. Interfacialrheological material properties must be measured to appreciate their role incontrolling the stability of the interfaces. Particularly particles display a intriguingability to stabilise foams and emulsions. In such systems complex interfacialmicrostructure leads to rheological complexity. Interfacial rheologicalcharacterization relies on the development of tools with the sensitivity to respond tosmall surface stresses in a way that isolates them from bulk stresses. In this work wewill first discuss how proper rheological material functions for interfaces can bemeasured, in shear, extension and dilation. subsequently we will study some classesof 2D suspensions and their intriguing rheological properties. Their role in complexmulti structured materials will be discussed.Colloidal gels and glassesDavid A. WeitzDepartment of Physics and SEAS, Harvard University,Cambridge, Massachusetts 02138, USAThis talk will present a summary of the properties of colloidal particles as a functionof both their volume fraction and their interaction energies. At high volume fractions,colloidal particles can form a glassy state, where structural relaxations becomeextremely slow so they system is solid like over measurable time scales. A solid-likestate is also achieved at lower volume fractions when an attractive interaction isintroduced. The overall behavior can be described by means of a phase diagram thatseparates solid- and liquid-like states as a function of interaction energy and volumefraction.30