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Rheolab Group

The Rheolab group deals with the behavior of complex fluids, mainly with structured fluids such as suspensions, micellar solutions, architecturally complex polymers, liquid crystals. We are interested in particular to the dynamic behavior of these structured fluids in linear and non-linear regime. Rheology, microscopy and scattering are the most important tools used in our experimental approach. Well defined model systems are of our interest. The main goal of our group is to understand the relation between microstructure and macroscopic response with the aim to tune the morphology at the micro/nano scale and obtain the preferred rheological behavior, at rest or during specific flow conditions. This is fundamental for industry in a way to gain the desired final product quality.

The main topics of our research groups are:

Suspensions

Usually we deal with spheres in structured water based solutions or polymer melts with the following aims: to understand the increase in viscoelasticity of the matrix tuning the filler shape and size in linear regime; in non-linear regime to tune the flow conditions in a way to induce specific microstructures (strings or rafts of spheres). Some articles on the topic by our group:

Micellar solutions

Surfactant molecules have the ability to self-assemble when dispersed in water due to the presence on the same molecule of a hydrophobic part and a hydrophilic one. It is possible to tune various parameters in a way to induce morphological transitions, such as the concentration of surfactant, PH, temperature and the content of a binding salt. In particular the latter is able to change the packing parameter of the molecules and, as such, induce morphological transitions (going from spherical micelles to linear and branched wormlike micelles). We are interested in these transitions, both at rest and in flow, both from a microscopic point of view and from a dynamic perspective. Transient behavior of wormlike micelles, bringing to non-linear phenomena (such as shear banding), is of our interest too, both via rheology and through scattering devices (collaboration with a group of Neutron Scattering in Julich, Germany). Some articles on the topic by our group:

Physical instability in structured fluids

Air bubbles are found in structured detergents at the end of the process. Structured detergents are complex systems made up by surfactant molecules (again!) and other components, such as solid fibers which reinforce the matrix, creating a strong network. Air bubbles, when incorporated during the process, can create a remarkable load to these detergents and induce instabilities. The type of instability depends on the rheological behavior of the fluids and, more specifically, on the load of the bubbles (s) compared to the detergent yield stress (sy). According to the entity of the load, there could be tunneling (s>sy) of the air bubbles or collapse of the entire network (s<sy). The tunneling is just the coming out of the bubbles from the fluid at the free surface liquid/air, without any type of instability. The collapse is characterized by the fact that the bubbles, during the rising up due to buoyancy within the fluid, can separate the fiber network by expelling out the solvent. To study the time evolution of the air bubbles in the fluid we built up a Macro Time Lapse Photography apparatus. Via an image analysis program it is possible to follow the particles trajectories. The aim is to understand the relation between the air bubbles distribution, the rheological characteristic of the matrix and the induced instability. Other research projects deal with polymer rheology, in particular with copolymers and architecturally complex polymers but also with liquid crystals and foams. See for example:

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