Self-assembly of Attractive One-patch Colloids

In this thesis we study the phase behavior of one-patch colloids. We employ the Kern-Frenkel potential [1] to model these particles and calculate their equilibrium phase diagrams by means of computer simulations and free energy calculations in combination with the floppy box method [2] in order to generate and predict crystal phases. In the first part of the thesis we introduce the simulational and theoretical framework we use. In the second part we present a systematic analysis of the phase behavior of Janus colloids. In our case, we refer to Janus particles as particles with one hemi-sphere of its surface acting as a hard sphere, while the other hemisphere is attractive. We present a thorough analysis of the effect of the length of the interaction range on the phase behavior investigating multiple interaction ranges ∆, specifically ∆ = 0.05σ, 0.1σ, 0.2σ, 0.3σ, 0.4σ and 0.5σ, where σ is the particle diameter. Despite the simplicity of the model, we report rich phase diagrams in all cases. We observe the crystal complexity to grow upon increasing the interaction range. However, up to the interaction range ∆ = 0.3σ we see identical or similar crystal structures. Consequently, we investigate the effect of the patch coverage fraction. We calculate phases diagram of short ranged one-patch colloids, namely coverage fractions of 30%, 50% and 60%. The exact interaction range is in this case 5% of the particle diameter. We report bilayer sheets formations for large patch coverage fractions and interestingly open low temperature crystals for small coverage fractions. Apart from the crystal structures, the gas-liquid critical point is also investigated using successive umbrella sampling. The last system studied in this thesis is a one-patch system spontaneously forming tubes [3]. The employed interaction range, is 50% of the particle diameter, and the patch coverage fraction in this case is 30%. We detect a crystal phase composed of these spontaneously formed tubes in small region of the phase diagram competing with another stable lamellar crystal structure [4]. The complete equilibrium phase diagrams are calculated and presented for all the mentioned cases. [1] Kern, N & Frenkel, D. (2003) Fluid–fluid coexistence in colloidal systems with short-ranged strongly directional attraction. J. Chem. Phys. 118, 9882–9889. [2] Filion, L, Marechal, M, van Oorschot, B, Pelt, D, Smallenburg, F, & Dijkstra, M. (2009) Efficient method for predicting crystal structures at finite temperature: Variable box shape simulations. Phys. Rev. Lett. 103, 188302. [3] Munaò, G, Preisler, Z, Vissers, T, Smallenburg, F, & Sciortino, F. (2013) Cluster formation in one-patch colloids: Low coverage results. Soft Mat- ter 9, 2652–2661. [4] Preisler, Z, Vissers, T, Smallenburg, F, Munaò, G, & Sciortino, F. (2013) Phase diagram of one-patch colloids forming tubes and lamellae. The Journal of Physical Chemistry B 117, 9540–9547.