ASSEMBLY OF PARTICLES ONTO RIGID CYLINDERS AND FLEXIBLE MEMBRANES: PROBING EFFECTS OF SURFACE CURVATURE AND DEFORMATION

In this thesis we explore two specific topics within the broad field of particle adhesion. First, we examine the effect of substrate shape and geometry on the self assembly of adsorbed particles, by performing molecular dynamics simulations of interacting particles constrained to the surface of cylinders of varying diameters. We find the diameter of the cylinder imposes a constraint on the shape and crystallographic orientation of the self-assembled lattice, essentially determining the optimal arrangement of particles a priori. We propose a simple one-dimensional model to explain the optimal arrangement of particles as a function of the particle interaction potential and the physical size of the constraining cylinder. We next investigate the stiffness of these cylindrical lattices, and find that thin cylindrical crystals are anomalously softer than large ones. We then propose this effect is a consequence of the geometric arrangement of particles in a tight cylindrical shape, and quantify how the stiffness depends on the circumference of the cylinder and on the strength of interaction between the particles. Second, we explore how adhesion of particles can reshape the substrate, for the purpose of designing novel functional materials. We perform experiments exposing cationic nanoparticles to lipid bilayer vesicles, where we vary the adhesion energy between the two by adjusting the fraction of anionic lipid (DOPS) in the otherwise zwitterionic lipid (DOPC) bilayer membrane. We find two distinct types of behavior: when the DOPS content of the membrane is 5% or higher, the high adhesion energy causes the nanoparticles to disrupt the vesicles upon adsorption. When the DOPS content is 4% or less, the adhesion of nanoparticles caused the vesicles to adhere to one another and form a rigid liposome gel. We propose that these two behaviors are explained by a transition from a partial wrapping of the nanoparticles to their complete envelopment by the membrane when the DOPS content exceeds 4.5%. We also detail methods for producing large quantities of the vesicle gel using cationic polymers in place of the nanoparticles. These findings could be used to to engineer new solid, semi-permeable materials that can encapsulate cargo, or to create cargo-carrying liposomes with the ability to rupture on trigger

Colloidal rods and spheres in partially miscible binary liquids

Different scenarios for assembling rod-like and spherical colloidal particles using binary mixtures of partially miscible liquids were investigated experimentally. Suitable rod-like colloids were developed first. The subsequent studies of colloids in binary liquids consisted, on one hand, of systems where particles were partially wetted by both phases and, on the other hand, of systems where particles were completely wetted by the minority phase. A simple method to prepare large quantities of micrometer-sized akagan eite-silica core-shell rods was developed. These were proven to be very versatile, with the possibility of modifying their properties on different levels. The aspect ratio is simply controlled by a gradual growth of the silica shells. From them, hollow silica rods and rods with an increased responsiveness to a magnetic field could be obtained in straightforward ways. Bijels were prepared by trapping rod-like particles on a percolating liquid-liquid interface. The familiar bicontinuous organization of liquid domains was observed after structural arrest. At a fixed volume per particle it is demonstrated that for rod-like particles the domain size decreases faster with increasing quantity of particles than in the case of spherical particles. Additionally, the packing of the rods at the interface was elucidated, revealing several characteristic features. In particle-stabilized droplet emulsions rapid evaporation of the continuous phase and eventual full mixing of the liquid phases can leave a cellular network of particles. The formation and eventual stability of these networks were investigated in detail with confocal microscopy. When colloids are completely wetted by the minority component of an asymmetric binary mixture there can be substantial temperature and composition regimes outside the binodal where shear-induced aggregation can take place. This happens as adsorbed layers present at the particle surfaces coalesce and bind particles through a liquid bridge. Depending on particle concentration, percolating networks can form of rods wetted by the minority phase after temperature quenching such a system just across the binodal

Advances in Cholesteric Liquid Crystals

With their helical structure, cholesteric liquid crystals figure prominently in liquid crystal science. The selective reflection of light is their flagship property, and they offer a myriad of applications as advanced optical materials with multiscale properties. The cholesteric structure is also a ubiquitous design in the animal and plant kingdoms. This book contains eight contributions on fundamental investigations about defects, textures and structures of cholesteric materials, and experimental studies aimed at applications such as temperature sensors, head-up displays for improving automobile driving safety, or smart windows