Abstract
This thesis focuses on the liquid crystal phase transitions of colloids with anisotropic shapes such as rods, boomerangs, and cuboids. Colloids are solute particles with dimensions in the range from several nanometers to a micrometer that are suspended in a solvent. These colloids experience Brownian motion due to collisions with solvent particles, and so explore their configuration space. The colloids can form analogous phases to molecular systems, such as liquid and crystal phases as well as intermediate socalled liquid crystal phases. For example, a liquid crystal phase commonly formed by long rodlike colloids, the nematic phase has longrange orientational order but no positional order. The phase that the colloids form depends on the thermodynamic properties such as number density as well as the interactions between the colloids. We focus on repulsive colloidal interactions, namely "hard" interactions due to the fact that the colloids cannot overlap. The equilibrium phase behavior is calculated for a given system using the theoretical framework of density functional theory within the second or third virial approximation.
In Chapter 2, we study the phase behavior of weakly and strongly charged hard rodlike colloids. Additionally, we investigate the stability of the nematic phase with respect to twist deformations. We then shift our focus to hard particles of various shapes less symmetric than rods. In Chapter 3, we study flexible "boomerangs," i.e., two rods joined at one end that can fluctuate around a certain preferred interarm angle. Here our focus is on biaxial nematic phases and how flexibility affects their stability. In Chapter 4, we investigate the homogeneous phases of rigid boomerangs as well as their limit of stability with respect to smectic phases by performing a bifurcation analysis. In Chapter 5, we study the prolate, oblate, and biaxial nematic phases of cuboids within second and thirdvirial theory, and compare our results to recent simulations. Then, in Chapter 6 we consider the sedimentation of a binary mixture of thick and thin rods, and build "stacking diagrams," which describe the sequences of phases that appear due to gravity. Finally, in Chapters 7 and 8, we study the percolation transitions of various shapes of colloidal particles in the isotropic phase. Specifically, in Chapter 7 we investigate the effect of kink and bend deformations on the percolation threshold of rodlike particles and in Chapter 8 we calculate the percolation thresholds of polygonal rods and platelet
In Chapter 2, we study the phase behavior of weakly and strongly charged hard rodlike colloids. Additionally, we investigate the stability of the nematic phase with respect to twist deformations. We then shift our focus to hard particles of various shapes less symmetric than rods. In Chapter 3, we study flexible "boomerangs," i.e., two rods joined at one end that can fluctuate around a certain preferred interarm angle. Here our focus is on biaxial nematic phases and how flexibility affects their stability. In Chapter 4, we investigate the homogeneous phases of rigid boomerangs as well as their limit of stability with respect to smectic phases by performing a bifurcation analysis. In Chapter 5, we study the prolate, oblate, and biaxial nematic phases of cuboids within second and thirdvirial theory, and compare our results to recent simulations. Then, in Chapter 6 we consider the sedimentation of a binary mixture of thick and thin rods, and build "stacking diagrams," which describe the sequences of phases that appear due to gravity. Finally, in Chapters 7 and 8, we study the percolation transitions of various shapes of colloidal particles in the isotropic phase. Specifically, in Chapter 7 we investigate the effect of kink and bend deformations on the percolation threshold of rodlike particles and in Chapter 8 we calculate the percolation thresholds of polygonal rods and platelet
Original language  English 

Awarding Institution 

Supervisors/Advisors 

Award date  10 Sept 2018 
Publisher  
Print ISBNs  9789039370216 
Publication status  Published  10 Sept 2018 
Keywords
 liquid crystals
 colloids
 biaxial nematics
 rods
 boomerangs
 cuboids
 percolation
 sedimentation