Recent research and experiments 
(You may want to download a free Quick Time movie player to vizalise the movie links)

A new Flexure-based Microgap Rheometer (FMR) 

with  Gareth McKinley

Built a new Flexure-based Microgap Rheometer (FMR) that allows the determination of the viscometric properties of small fluid samples (<10 microliter) in adjustable gaps that cover meso-scale dimensions of 200 micrometer down to micro-scale dimensions of 1 micrometer. This is enabled due to the usage of compound flexures, that minimize orthogonal displacement, and the application of white light interferrometry, which assures parallelism and allows absolute gap determination.

Modeling of elasto-capillary necking and break-up. 

with Jens Eggers, Marco Fontel & Gareth McKinley

Developement of a 1-D model of the necking in capillary break-up experiments on the basis of microscopic imaging of the self similar structure close to the singularity of the break-up point. 

Capillary break-up of liquid columns

with José Bico, Gareth McKinley & Vladimir Entov

Dripping of a jelly liquid

Concentrated surfactant solutions eventually exhibit particular molecular structures (“worm like micelles”) which lead to a jelly liquid. The material behaves as a soft elastic solid when a light stress is applied but flows as a liquid under higher stresses. 

When a droplet of such a liquid drips from a pipette, a long thread connects the droplet to the pipette and progressively necks and breaks down when the thread reaches a certain diameter.

Click on any picture to watch a video (4Mo).

Jet break-up

A jet of liquid is unstable because of surface and usually breaks into small droplets. The addition of a tiny quantity of polymer provides an additive elastic stress which stabilizes the liquid column. 

The snapshots represent a jet of water containing traces of hydrophilic polymer (polyacrylamide). The droplets are formed but remain connected by a thin thread. The first droplet then “eats” its followers until it detaches.

Click on the picture to watch a video (4.5Mo).

Gelation mechanism of (1,3)(1,4)-b-barley glucan in beer 

with N. Böhm  & W.-M. Kulicke

The formation of microgels during the beer brewing process and the clogging of filters in the final filtration result in a lower quality and throughput volume. The investigation of the gelling mechanism of barley (1,3)(1,4)-b-glucan is leading to the developement of new and improved methods in the brewing process 


New rheo-optical techniques

with U. Reinhardt and W.-M. Kulicke

Modulated polarized laser light allows for highly precise detection of birefringence and molecule orientation in flow fields. However the highly delicate and sensitive setups do not allow for an easy industrial application of these techniques. New modulation principles and robust apparati will overcome these barriers 

Viscoelastic properties of silk dope of bombyx mori and nephalia clavipes

with Nicola Kojic and Gareth McKinley

Silkworm and Spider silk contains about 60% of a crystalline repeating polypeptide sequences (GAGAGS) connected by amino acids with bulkier sidechains that do not crystallize and show superior mechanical properties compared to synthesized polymers. Although the liquid crystalline character of the silk dope has been observed, the viscoelastic properties of the silk dope prior to spinning, which determine the extrusion and spinning process, still need to be investigated.