Berlin 2008 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 28: Micro and Nano Fluidics III: Migration and flow
CPP 28.4: Talk
Thursday, February 28, 2008, 17:30–17:45, C 264
X-ray optics with microfluidics: Stabilization of gas bubbles by surface ordering and freezing — •Yasutaka Iwashita1, Christian Bahr1, Ralf Seemann1,2, and Stephan Herminghaus1 — 1MPI for Dynamics and Self-Organization, D-37073 Göttingen — 2Experimental Physics, Saarland University, D-66041 Saarbrücken
Compound refractive lenses (CRL), which are composed of many lenses of small radii in a row embedded in a solid medium, have been developed as X-ray lenses (A. Snigirev et al. [1]). CRL has numerous advantages as X-ray optics: It is robust, easy to align and to operate, and can be used for hard X-rays.
To broaden the possibilities and functions of CRL, we propose a "dynamic CRL": This is composed of gas bubbles in a liquid as lenses, where the bubbles are generated and flowing consecutively in a microfluidic device. Due to the continuous renewal of the materials, this system leads to a high stability against high X-ray intensities. Furthermore, the variation of bubble shape controlled via flow parameters allows in-situ optimization of the optical properties of the system.
Here we study the stabilization of gas-liquid foam in microfluidic devices by surface freezing of n-alkanes and surface ordering of liquid crystals. These systems have great advantages for dynamic CRL:(i) X-ray transmission is high and (ii) gas bubbles can be stabilized without surfactants. As a result, we succeeded in stabilizing gas-liquid foam by surface freezing and ordering, and in controlling the foam structure.
[1] A. Snigirev, V. Kohn, I. Snigireva and B. Lengeler, Nature 384(6604), 49(1996)