Non-equilibrium formation of the cubic Pn3m phase in a monoolein/water systemM. Rappolt1, G. M. Di Gregorio2, M. Almgren3, H. Amenitsch1, G. Pabst1, P. Laggner1 and P. Mariani2
1 Institute of Biophysics and X-Ray Structure Research, Austrian Academy of Sciences Schmiedlstraße 6, 8042 Graz, Austria
2 Dipartimento di Scienze Applicate ai Sistemi Complessi, Università Politecnica delle Marche - Via Ranieri 65, 60131 Ancona, Italy
3 Department of Physical Chemistry, Uppsala University PO Box 579, 75123 Uppsala, Sweden
received 31 March 2006; accepted in final form 29 May 2006
published online 16 June 2006
Time-resolved small-angle X-ray diffraction experiments have been carried out to investigate the transformation from the cubic gyroid Ia3d to the cubic diamond Pn3m phase. The transition was induced by rapid addition of water to a monoolein/water system changing the initial water concentration of 26% w/w to excess of water conditions. The transformation proceeds in two steps: at the beginning, the two cubic mesophases have a strongly differing lipid/water composition and are accompanied by an intermediate phase. This phase vanishes as the ratio of cell parameters exceeds 1.50. Thereafter, the transition continues by a direct nearly isoareal transformation of the cubic minimal surfaces. Lateral area per lipid molecule, molecular shape and principle curvatures are about the same in this regime.
61.30.St - Lyotropic phases.
87.15.He - Dynamics and conformational changes.
61.10.Eq - X-ray scattering (including small-angle scattering).
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