Thu 16 Feb 2017 – 3:30 pm (Murdoch University, Senate Conference Room)

Entropic self-assembly of bicontinuous structures : the gyroid … and more?

Mr Philipp Schönhöfer – Murdoch University

Note: Philipp is a PhD candidate in the School of Engineering and IT, and this talk is part of his confirmation of candidature process.

Many biological and synthetical systems  (like lipid/water mixtures [1] and di-block copolymers [2]) form highly complex and symmetric triply-periodic, bicontinous structures by enthalpic self-assembly. Studies by Barmes et al. [3] and Ellison et al. [4] showed that one of these structures, the so called Ia(-3)d double gyroid, can also be generated in equilibrium systems of hard pear-shaped particles with suitable tapering and aspect ratio and consequently systems where entropy is the key factor and no attractive forces are needed.

Performing MD and MC simulations, we  have reproduced the spontaneous formation of the gyroid by hard tapered particles and generated a density-tapering phase diagram. To compare the differences between the enthalpically and entropically driven processes further, we studied the geometrical and morphological properties of the gyroid phase, using scattering functions and Voronoi tessellations. Through this, we show that the formation mechanisms prevalent in this entropy-driven system differ from those found in systems which form Gyroid structures in nature.

Subsequently, hard spheres which shall take up the role of solvent to model mixtures with a solvent are introduced into the simulations. With an explicit solvent the system should be complex enough to model most common phenomena in cubic phases. In this particular case we especially examine a potential stabilizing influence of spheres on the gyroid structure. From a biological point of view this will give information on the formation of other bicontinous structures like the Pn3m double diamond or unbalanced membranes (eg. if the generation of the I4(1)32 gyroid structure is solez entropy driven). Hence, systems with different concentrations and sphere sizes are analysed.

[1] J. M. Seddon and R. H. Tepler, Phil. Trans. R. Soc. A 344(1672), 377–401 (1993).

[2] M. W. Matsen and M. Schick, PRL 72(16), 2660 (1994).

[3] F. Barmes, M. Ricci, C. Zannoni, and D. J. Cleaver, Phys. Rev. E 68, 021708 (2003).

[4] L. J. Ellison, D. J. Michel, F. Barmes, and D. J. Cleaver, Phys. Rev. Lett. 97, 237801 (2006).