Seminars

We invite people to join us in our soft matter & photonics seminars. The meetings are informal and meant to present and discuss recent work of visiting scientists and group members.  If you would like to present your work in our seminar-series or if you wish to be informed of the seminar schedule by e-mail, please send an e-mail to Veronique Trappe.

   

 

 Seminars, Winter/Spring 2013

Thursday, January 17, 2013
10:30, Physics 0.51

Martin Medebach,

Physical Chemistry, Chemical Center, Lund University, Getingevägen 60, 22100 Lund, Sweden

D-Echo-DLS Flat Cell Light Scattering Instrument and FFT – Raman DLS

In this presentation I will give an overview about the development and performance of the 3D-Echo-DLS Flat Cell Instrument (3D-Echo-DLS –FCLSI) and about the state of the art of the Raman-DLS.
The 3D-Echo-DLS –FCLSI is a powerful instrument to measure the dynamics of high concentrated and turbid colloidal suspensions. The intercept of the correlation function is increased by a factor of 4 by crossed polarization filters. The multiple scattering is strongly reduced by a thin sample cell of a thickness of only 10μm. With this setup a non-index matched emulsion with weight fraction of 75% and droplet size of 1.4μm (white paste) can still be measured with an intercept of 0.52. The maximum possible measurement time, which is equal to the maximum relaxation time that can still be measured with this instrument lies around 30000sec.
Raman-DLS is a promising technique to measure the dynamics of a mixture of particles with different chemistry. The idea is to select a Raman line that is typical for particle A and to measure the intensity- auto-correlation function for this Raman line. The same can be done for the other particle types B, C,... Now, one can determine if particles are moving separately or together (aggregation) and the diffusion coefficient of each particle component can be extracted. This new technique is at the moment under construction and first üreliminary results will be presented.

Friday, March 1, 2013
9:00,  Physics 0.51

Adrian-Marie Philippe

Laboratoire d’Énergétique et de Mécanique Théorique et Appliquée, Nancy Université

Rheological study of 2D very anisometric colloidal particles suspensions: from shear induced orientation to viscous dissipation

We investigate the evolution with shear of the viscosity of aqueous suspensions of size-selected natural swelling clay minerals, for volume fractions extending from isotropic liquids to weak nematic gels. Such suspensions are strongly shear-thinning, a feature that is systematically observed for suspensions of non-spherical particles and that is linked to their orientational properties. We then combined our rheological measurements with small angles x-ray scattering experiments, that, after appropriate treatment, provide the orientation distribution function of the clay particles.
Whatever the clay nature, particle size and volume fraction this orientational field was shown to only depend on a non-dimensional Péclet number defined for one isolated particle as the ratio between hydrodynamic energy and Brownian thermal energy. The measured orientational fields were then directly compared to those obtained for an isolated infinitely thin disk through a numerical computation of the Fokker-Plank equation. We then explored the links between orientational fields and viscosity and showed that for particles with size higher than 250 nm, the experimentally measured viscosity could be directly deduced from the calculation of the viscous dissipation around one isolated particle. However, the thus calculated viscosities deviate from the experimental ones for smaller particles, and such deviation increases with decreasing particle size.

 

Wednesday, March 6, 2013
17:15,  Physics 0.51

Colloquium

Juan José Saenz,

Autonomous University, Madrid

Optically induced 'negative Forces': Laser Tractor Beams

Monday, March 17, 2013
ca. 16 h (tba)

AMI-Colloqium

Justin J. Cooper-White

University of Queensland, Australia

Engineering the cellular microenvironment

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that have the ability to differentiate into all mesenchymal tissues, including bone, muscle, cartilage, tendon and fat. Pluripotent stem cells (hESC, iPSC) have the potential to form all tissues in our body. These cells are ideal candidates for a multitude of regenerative medicine applications, and further, for the development of new insights into disease etiology and progression and for cell-based drug discovery, screening and formulation design platforms.

Friday, April 19, 2013
10:30,  Physics 0.51

Lucio Isa

ETH Zürich

Adsorption energies of poly(ethylene oxide) based surfactants and nanoparticles on an air-water surface
 
The self-assembly of polymer-based surfactants and nanoparticles on fluid-fluid interfaces is a process central to many applications including dispersion stabilization, creation of novel 2D materials and surface patterning. Very often these processes entail the compression of interfacial particle or polymer monolayers to obtain the desired material microstructure; at high surface pressures, soluble objects may desorb from the interface and therefore a direct way of measuring adsorption energies becomes of high interest. Moreover, a geometric description linking adsorption energy and wetting properties through the definition f a contact angle can be established for rigid nano or microparticles, but such description breaks down for deformable or aggregating objects. Finally, in the presence of repulsive interactions between particles, the adsorption energy calculated from purely geometrical arguments as mentioned above and the energy required to desorb particles from the interface may not necessarily be the same. I will present some recent data where we used a novel microtensiometer tool in combination with traditional surface pressure measurements to measure directly the desorption of various types of PEO-based polymers and nanoparticles. Our data show a linear scaling between molecular weight and adsoprtion energy for PEO chains whose values depend on the sub-phase composition. Moreover, for PEO-stabilized nanoparticles, the desorption surface pressure corresponds to the saturation surface pressure for spontaneously adsorbed monolayers and corresponds to trapping energies of ~103 kT. The values of the surface concentration at desorption confirm particle deformation, as observed using x-ray microstructural characterization.

 

 

Internal Seminars, Winter/Spring 2013
Friday, xxxx, 2013
9:00,  Physics 0.51




Friday, xxxx 12, 2013
9:00,  Physics 0.51
   

 

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