Doctor of Philosophy, Case Western Reserve University, 2019, Physics

Soft condensed matter is the study of flexible materials that change their shape under the influence of a weak force. Typical examples are polymers and liquid crystals. Chromonic liquid crystals consist of molecules having a hydrophobic flat aromatic core to which have been attached ionic groups or non-ionic groups. These disk-like molecules self-assemble into ordered phases in the presence of solvents, aggregating in a face-to-face fashion, and creating stacked linear molecular aggregates. The degree of self-organization into columns depends on the concentration, temperature, and pressure. Depending on the types of terminal groups, the molecules can be dissolved in organic solvents or water. A theoretical study was performed to model the detailed effects of adding stacking, translation, and rotation energy on the length distribution of chromonic liquid crystals. A second derivative test was done to prove that all the solutions for isotropic phases are at a global minimum of the free energy. The free energies and length distributions for various nematic phase formulations are presented. Free energy and length distribution for both Maier-Saupe and Onsager interactions are presented. The free energy and length distribution for considering I-N phase co-existence and no phase co-existence are presented. It is shown that the nematic phase solutions all lead to a first-order phase transition. The nematic phase solution with the Maier-Saupe interaction causes the averaged aggregate length to increase when the system transitions from the isotropic phase to the nematic phase, while the nematic phase solution with the Onsager interaction causes the averaged aggregate length to decrease. Another major component of this thesis is the study of glass transitions. An analytical study that aims to describe the mean squared displacement at low temperatures is presented. The short-time and long-time limit of the analytical solution are discussed. Then, an app (open full item for complete abstract)

Committee: Philip Taylor (Advisor); Mesfin Tsige (Advisor); Wojbor Woyczynski (Committee Member); Harsh Mathur (Committee Member) Subjects: Mathematics; Physics; Polymers; Statistics

Doctor of Philosophy, University of Akron, 2005, Polymer Engineering

A novel nanolithography technique is developed for nanoscale patterning of polymers: atomic force microscope assisted electrostatic nanolithography (AFMEN). In AFMEN, nanostructures are generated by mass transport of polymeric material within an initially uniform, planar film. The combination of localized softening of attolitres of polymer, a strongly non-uniform electric field to polarize and manipulate the soften dielectric, and single-step process methodology using conventional atomic force microscopy (AFM), establishes a new paradigm for polymer nanolithography. We develop a basic theoretical understanding of the processes associated with AFMEN and present modeling of the relevant phenomena. The analysis of polymer heating indicates that the AFMEN resolution is not directly limited by the radius of the AFM tip, which is distinctly different from alternative AFM–based lithographic techniques. Instead, the feature size depends critically on the thermal characteristics of the polymer, such as its thermal conductivity. The dielectric properties of the polymer play a secondary role, affecting the magnitude of the electric field but do not directly impact the feature size. The nanostructure shape is determined by the competition between the ponderomotive forces acting on the dielectric material in non–uniform electric field, and the polymer surface tension. An exact analytical solution, as well as numerical solutions, are determined for the electric field distribution in the tip–sample junction, which allow prediction of the nanostructure geometry. The response of the AFM tip during the nanolithography process is investigated. An analysis of the free energy of the system, comprising AFM tip, sample surface and water meniscus, shows that the tip is spontaneously lifted away from the polymer surface. The mechanical work required to lift the tip is drawn from the energy of electric field. In addition, water condensation in the proximity of nanoscale asperities such as an (open full item for complete abstract)

Committee: Sergei Lyuksyutov (Advisor); Erol Sancaktar (Advisor); Arkadii Leonov (Other); Robert Mallik (Other); Sadhan Jana (Other) Subjects: