Dokument: Colloidal Crystallization under Confinement
|Colloidal Crystallization under Confinement
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|Wissenschaftliche Abschlussarbeiten » Dissertation
|Dipl.-Phys. Oguz, Erdal Celal [Autor]
|Prof. Dr. Löwen, Hartmut [Betreuer/Doktorvater]
Dr Messina, Rene [Gutachter]
|Colloids, Confinement, Crystallization
|500 Naturwissenschaften und Mathematik » 530 Physik
|This thesis at hand deals with crystalline phases of colloidal particles under confinement. In particular, we mainly investigate the equilibrium structures of confined colloidal crystals, and present recently obtained results in five self-contained chapters. These five chapters, and thus the thesis, can be divided into three parts, each characterized by the type of the confinement.
In the first part, containing the Chapter 1, we applied a hard cylindrical confinement to a model system of point-like particles interacting via a Yukawa pair potential. We investigate the ground state stability phase diagram of the crystalline Yukawa system by using lattice sum minimizations. The cylindrical confinement displays the origin of the quasi-one-dimensionality; By continuously increasing the cylinder radius from zero to a finite value, we open the way to an intermediate regime between one and three dimensions. In this regime, we obtain chiral and achiral helical structures, which help a lot to understand the nature of e.g., biomolecules such as DNA.
In the second part (Chapter 2), we combine real-space experiments (by Reinmüller et al) and Brownian Dynamics computer simulations in order to study the driven crystallization of charged particles in two-dimensional flow fields in aqueous solvents. These flow fields occur due to electrolyte gradients caused by cation exchange resin fragments. Colloidal macroparticles follow the flow. Consequently, the crystallization takes place at these fragments, acting as seed particles.
Regarding the experimental situation, the point-like Yukawa particles in simulations are exposed to an attractive,
long-ranged circular trapping potential to mimic the solvent flow. Good agreement is achieved between experiments and
simulations. As a result, we obtain mono- and polydomain crystals with corresponding grain boundaries, depending on the shape of the seed.
The third part of this thesis comprises the Chapters 3,4, and 5.
Here, the confinement is given by a hard slit, i.e., two parallelly aligned hard flat walls. This special confinement gives rise to a quasi-two-dimensional system, which interpolates between two and three dimensions. Three different pair interactions are considered in three different chapters, all involving the quasi-two-dimensionality: In Chapter 3, we investigate the yero-temperature crystalline phase diagram of unscreened Coulomb particles embedded in a parabolic soft potential (in addition to the hard slit). By energetic considerations using lattice sum minimization methods, we figure out stable mono-, bi-, and multilayers. In Chapter 4, we analyze crystalline multilayers of charged colloids confined between two glass
plates. Here, we combine experiments (by Reinmüller et al) and lattice sum minimizations. Charged colloids are modelled with a Yukawa potential, whereas the wall-particle repulsion is assumed to be of hyperbolic cosine form in accordance to the linear screening theory. We obtain complex phases (e.g., the vertically aligned triangular layers hcp⊥ equivalent to hcp(110)), which are not present in three-dimensional bulk. Chapter 5 addresses the packing problem of confined hard spheres.
By combining experiments (by Ramiro-Manzano et al), Monte Carlo computer simulations (by Marechal), and theory (using a recently reported penalty method), we investigate the dense packed crystalline structures in a hard slit. We achieve an excellent agreement between the three approaches, and recover the novel adaptive phases,
which brings new opportunities and insights into the field of the packing problems.
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|Mathematisch- Naturwissenschaftliche Fakultät » WE Physik » Theoretische Physik
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