Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 7: POSTERS Rheology

CPP 7.15: Poster

Monday, February 25, 2008, 16:45–19:00, Poster A

Unusual growth exponent in liquid crystal foams — •Torsten Trittel, Victor Aksenov, and Ralf Stannarius — Otto-von-Guericke-Universität Magdeburg

We investigate foams made from pure thermotropic liquid crystals and observe a new type of scaling behaviour during foam coarsening. 2D foams are prepared in thin cells and studied by digital image anylysis. We calculate the temporal evolution of the mean bubble radius ⟨ R(t) ⟩ and find a scaling behaviour with ⟨ R(t) ⟩ ∝ t^α. In ordinary soap foams, the growth exponents are α=1/3 (wet foams, circular bubbles) and α = 1/2 (dry foams, polygonal bubbles), respectively. Our bubbles have a polygonal shape like in a dry foam, but we observe an anomalous growth exponent α ≃ 0.20 in the smectic phase. This is not compatible with the classical theories of bubble growth in foams, neither for dry nor for wet foams. In the nematic phase, coalescense dominates the evolution and the foam collapses so fast that one can not determine a steady scaling growth exponent.