Home

Example of phase-separated system. Left image: four phases can be observed in this system, however in the picture it is hard to see the boundary between the nematic and the isotropic. Right image: sample between crossed polarizers, note that it is possible to identify the nematic phase owing to its birefringency.

What?

I study systems of charged platelets and the phases that they form when dispersed in salt-water solutions. As charged platelets I use a synthetic clay which consists of around hundred nanometer thick particles.

When these systems of clay in aqueous solution are allowed to settle under gravity, they will separate into different coexisting phases, among them an Isotropic Gel (disordered particles) and a Nematic one (particles have long-range orientational order). My interest is on these phases and the transitions between them.

Why?

Clay has been a useful, ubiquitous material throughout history. Despite its many industrial applications – which range from oil-related aspects to cosmetics – fundamental studies of the complex physical phenomena of clays and resulting applications are merely at its beginning.

Hence, from our studies we want to understand the interactions and resulting structures, and thus be able to manipulate properties of similar colloidal platelet and rod-like systems.

How?

In order to study these colloidal systems I employ X-rays Scattering techniques (SAXS and WAXS).

We have our own SAXS apparatus at NTNU, however for most experiments on these systems we need high intensities; hence we are users of the following experimental facilities: the European Synchrotron Radiation Facility (ESRF) in Grenoble–France; and the Brazilian Synchrotron Light Laboratory (LNLS) in Campinas-Brazil.

Dr. Yves Méheust is actively involved in this project as its co-supervisor.

NTNU – Institutt for fysikk

Hoegskoleringen 5, E3-138

7491 Trondheim, Norway

Contact info:

Phone: (+47) 7359 1858

Fax: (+47) 7359 7710

E-mail: davi (dot) fonseca (at) phys.ntnu.no