Contact Angles And Contact Lines Around Particles At Isotropic And Anisotropic Liquid Interfaces, 2015 University of Massachusetts - Amherst

#### Contact Angles And Contact Lines Around Particles At Isotropic And Anisotropic Liquid Interfaces, Nesrin Senbil

*Doctoral Dissertations*

Liquid interfaces, capillarity and self-assembly of particles at interfaces are important in nature and technology. When a particle is adsorbed to a liquid interface, the contact line of the particle with the liquid interface and the associated contact angle are the crucial parameters that drive assembly of the particles. We looked at how the shape of the liquid interface and the shape of the particle affect the contact angle and the shape of the contact line. We used millimeter-sized PDMS-coated glass spheres and measured the contact angles at isotropic (planar) and anisotropic interfaces (saddle and cylindrical in shape). Anisotropy of ...

Simulating An Anomalous Prediction Of The Boltzmann Equation, 2015 University of Colorado, Boulder

#### Simulating An Anomalous Prediction Of The Boltzmann Equation, Andrew Eric Sharp Barentine

*Undergraduate Honors Theses*

There is an anomalous prediction of the Boltzmann equation that monopole motion in an isotropic and harmonic potential will not damp. We have implemented a modification to our Time-Averaged Orbiting Potential (TOP) Trap, which we call the zzTOP Trap. Although this modification allows us to reach unprecedented levels of isotropy, it is still not perfectly isotropic. There are several methods of proving that the monopole motion in isotropic and harmonic potentials is undamped, but there are no analytic descriptions of monopole motion in slightly anharmonic and slightly anisotropic potentials. To this end, I have programmed a semi-classical Monte Carlo simulation ...

Ultrafast Dynamics Of Single Crystal And Polycrystalline Vo2, 2015 University of Colorado, Boulder

#### Ultrafast Dynamics Of Single Crystal And Polycrystalline Vo2, Meaghan Daly

*Undergraduate Honors Theses*

In recent decades, interest has rapidly developed in the group of materials known as strongly correlated electron systems. These systems exhibit numerous startling behaviors ranging from high temperature superconductivity to the topic of this thesis: metal-insulator transitions, specifically in the material vanadium dioxide (VO2). Unfortunately, due to wide variations within and between samples, it has been difficult to determine the underlying cause of such a phenomenon. In an effort to establish more consistent discrepancies between different growth methods, I have studied two samples of VO2 : a single crystal and a polycrystalline thin film. The differences observed in the responses of ...

Emergent Structure Of Multi-Dislocation Ground States In Frustrated Assemblies, 2015 University of Massachusetts - Amherst

#### Emergent Structure Of Multi-Dislocation Ground States In Frustrated Assemblies, Amir Azadi

*Doctoral Dissertations*

In this dissertation we study the emergent patterns of multi-dislocation ground states in two geometrically related classes of frustrated assemblies, twisted filament bundles and crystalline spherical cap. We discuss the fundamental role played by characteristic patterns of dislocations in restructuring the ordered phase of theses geometrically frustrated systems in the presence of external stresses. Our analysis on the formation of grain boundary scars leads to universal predictions for the features of defect patterns and their underlying energetic principles.

Mechanics Of Helical And Fabric-Like Mesostructures From Polymer-Nanoparticle Hybrids, 2015 University of Massachusetts - Amherst

#### Mechanics Of Helical And Fabric-Like Mesostructures From Polymer-Nanoparticle Hybrids, Jonathan T. Pham

*Doctoral Dissertations*

Hierarchical structures developed from nanoscale building blocks offer an excellent opportunity to control properties on *all* length scales, from the molecular level up to the macroscale. Many beautiful examples in Nature have demonstrated the significance of controlling geometry and mechanics on small length scales to control function on an organism-level, shown by the strength of bones, the toughness of a mollusk's shell, or the gecko's ability to climb walls. Inspired by stunning examples in both Nature and common man-made materials and structures, we assemble polymers and inorganic nanoparticles (NPs) with well-defined surface chemistry into long ribbons and fabric-like ...

Geometry And Thermodynamics Of Filament Bundles, 2015 University of Massachusetts - Amherst

#### Geometry And Thermodynamics Of Filament Bundles, Isaac Bruss

*Doctoral Dissertations*

In this dissertation I present a study of the geometry and energetics of bundles composed of flexible cohesive filaments. This is a general class of materials, both biological and artificial, existing across many length scales. The aim of this thesis is to investigate the interdependence between the 2D organization of filaments in a bundle’s cross section, and the 3D structure, with an emphasis on the twisting mode of deformation. First we present a model of filament contacts and interactions, which we employ in numerical simulations to study the connection between the ground state energies of constant-pitch bundles and their ...

Step Growth And Meandering In A Precursor-Mediated Epitaxy With Anisotropic Attachment Kinetics And Terrace Diffusion, 2014 Western Kentucky University

#### Step Growth And Meandering In A Precursor-Mediated Epitaxy With Anisotropic Attachment Kinetics And Terrace Diffusion, Mikhail Khenner

*Mikhail Khenner*

Step meandering instability in a Burton-Cabrera-Frank (BCF)-type model for the growth of an isolated, atomically high step on a crystal surface is analyzed. It is assumed that the growth is sustained by the molecular precursors deposition on a terrace and their decomposition into atomic constituents; both processes are explicitly modeled. A strongly nonlinear evolution PDE for the shape of the step is derived in the long-wave limit and without assuming smallness of the amplitude; this equation may be transformed into a convective Cahn-Hilliard-type PDE for the step slope. Meandering is studied as a function of the precursors diffusivity and ...

Electromigration-Driven Evolution Of The Surface Morphology And Composition For A Bi-Component Solid Film, 2014 Western Kentucky University

#### Electromigration-Driven Evolution Of The Surface Morphology And Composition For A Bi-Component Solid Film, Mikhail Khenner, Mahdi Bandegi

*Mikhail Khenner*

A two PDEs-based model is developed for studies of a morphological and compositional evolution of a thermodynamically stable alloy surface in a strong electric field, assuming different and anisotropic diffusional mobilities of the two atomic components. The linear stability analysis of a planar surface and the computations of morphology coarsening are performed. It is shown that the conditions for instability and the characteristic wavelength and growth rate differ from their counterparts in a single-component film. Computational parametric analyses reveal the sensitivity of the scaling exponents to the electric field strength and to the magnitude of anisotropies difference.

Statistics Of The Island-Around-Island Hierarchy In Hamiltonian Phase Space, 2014 Technion-Israel Institute of Technology

#### Statistics Of The Island-Around-Island Hierarchy In Hamiltonian Phase Space, Or Alus, Shmuel Fishman, James Meiss

*Applied Mathematics Faculty Contributions*

The phase space of a typical Hamiltonian system contains both chaotic and regular orbits, mixed in a complex, fractal pattern. One oft-studied phenomenon is the algebraic decay of correlations and recurrence time distributions. For area-preserving maps, this has been attributed to the stickiness of boundary circles, which separate chaotic and regular components. Though such dynamics has been extensively studied, a full understanding depends on many fine details that typically are beyond experimental and numerical resolution. This calls for a statistical approach, the subject of the present work. We calculate the statistics of the boundary circle winding numbers, contrasting the distribution ...

Hi-Fidelity Simulation Of The Self-Assembly And Dynamics Of Colloids And Polymeric Solutions With Long Range Interactions, 2014 University of Tennessee - Knoxville

#### Hi-Fidelity Simulation Of The Self-Assembly And Dynamics Of Colloids And Polymeric Solutions With Long Range Interactions, Mahdy Malekzadeh Moghani

*Doctoral Dissertations*

Modeling the equilibrium properties and dynamic response of the colloidal and polymeric solutions provides valuable insight into numerous biological and industrial processes and facilitates development of novel technologies. To this end, the centerpiece of this research is to incorporate the long range electrostatic or hydrodynamic interactions via computationally efficient algorithms and to investigate the effect of these interactions on the self-assembly of colloidal particles and dynamic properties of polymeric solutions. Specifically, self-assembly of a new class of materials, namely bipolar Janus nano-particles, is investigated via molecular dynamic simulation in order to establish the relationship between individual particle characteristics, such as ...

Phase Transitions In Smectic Liquid Crystal Systems, 2014 California Polytechnic State University - San Luis Obispo

#### Phase Transitions In Smectic Liquid Crystal Systems, John Van Atta, Josh Ziegler

*Physics*

Liquid crystal systems show strong responses to small changes in both temperature and electric field. Changing these conditions can result in phase shifts and other similar behaviors. We study several theoretical models of smectic liquid crystals. The ideas and notation are first developed in basic polynomial models used to describe liquid crystal systems dependent only on temperature. Specifically, smectic-C to smectic-A phase transitions are examined in a fourth-order polynomial model. The bifurcations in the nonlinear equations are shown to correspond to the phase transi- tions in the system. Similar analytic techniques are then applied to a more complex model, based ...

The Impact Of Membrane Tension On Phase Separation And Solid Domain Properties In Model Multicomponent Vesicles, 2014 University of Massachusetts Amherst

#### The Impact Of Membrane Tension On Phase Separation And Solid Domain Properties In Model Multicomponent Vesicles, Dong Chen

*Doctoral Dissertations*

Multicomponent phospholipid membranes provide an ideal model to study the complex phase behavior of biological membranes. Giant unilamellar vesicles (GUV) formed by mixtures of two or more phospholipids have particular merit as model membranes because of their simplicity, operability, and ease of viewing phase separation and testing membrane mechanics. Until the research in this thesis, biochemistry and biophysical studies of phase separation in phospholipid membranes primarily addressed the influence of membrane composition on the transition temperatures and domain shapes. This thesis focuses on a commonly neglected variable - membrane tension, analogous to pressure in bulk materials, as an important parameter to ...

On The Crumpling Of Thin Sheets, 2014 Physics Department

#### On The Crumpling Of Thin Sheets, Anne Dominique Cambou

*Doctoral Dissertations*

The inner walls of mitochondria, cabbage leaves, and even the Himalayas are all examples of thin sheets: objects with a thickness much smaller than their length and width. Despite their differences in size and in material composition, similar patterns emerge when sheets are crumpled or forced into a small three-dimensional space. As the compaction progresses, the deformations focus into increasingly sharper features that look like the network of peaks and creases found on the surface of a balled up piece of paper. In this regime, external forces are straining the membrane, causing the elastic energy to localize while leaving most ...

Heterogeneous Rotational Diffusion Of A Fluorescent Probe In Lipid Monolayers, 2014 Wesleyan University

#### Heterogeneous Rotational Diffusion Of A Fluorescent Probe In Lipid Monolayers, Christina M. Othon

*Christina M Othon*

The rotational correlation time of the lipid probe 1-palmitoyl-2-{6-[(7-nitro-2-1,3-benzoxadiazol-4-yl)amino]hexanoyl}-sn-glycero-3-phosphocholine (NBD-PC) is measured using fluorescence anisotropy for two lipid species. We measure the rotational diffusion in a monolayer of 1,2-Didecanoyl-sn-glycero-3-phosphocholine (DPPC) which displays a phase transition at room temperature from the liquid expanded to the liquid-condensed phase. The constant rotational diffusion of the probe throughout the phase transition reflects the measurement of dynamics in only the liquid-expanded phase. We contrast the dynamic changes during this phase coexistence to the continuous density increase observed in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) at room temperature. We observe a non-exponential ...

Composition Dependence Of The Flory-Huggins Interaction Parameter In Polymer Blends: Structural And Thermodynamic Calculations, 2014 University of Tennessee - Knoxville

#### Composition Dependence Of The Flory-Huggins Interaction Parameter In Polymer Blends: Structural And Thermodynamic Calculations, Travis H. Russell

*Doctoral Dissertations*

Flory-Huggins Theory has been the basis for understanding polymer solvent and blended polymer thermodynamics for much of the last 60 years. Within this theory, a parameter (*χ*) [chi] was included to quantify the enthalpic energy of dispersion between distinct components. Thin film self-assembly of polymer melts and block copolymers depends critically on this parameter, and in application, *χ *has generally been assumed to be independent of the concentrations of the individual components of the system. However, Small-Angle Neutron Scattering data on isotopic polymer blends, such as polyethylene and deuterated polyethylene, have shown a roughly parabolic concentration dependency for *χ*. Therefore ...

Structural Dynamics And Charge Transport In Room Temperature Ionic Liquids, 2014 University of Tennessee - Knoxville

#### Structural Dynamics And Charge Transport In Room Temperature Ionic Liquids, Philip James Griffin

*Doctoral Dissertations*

Room temperature ionic liquids are an important class of materials due to their chemical tunability and numerous advantageous physicochemical properties. As a result, ionic liquids are currently being investigated for use in a wide array of chemical and electrochemical applications. Despite their great potential, however, the relationship between the chemical structure and physicochemical properties of ionic liquids is not well understood.

To this end, this dissertation presents experimental studies of the reorientational structural dynamics and charge transport properties of a variety of room temperature ionic liquids using quasielastic light scattering spectroscopy and broadband dielectric spectroscopy.

Studies of a series of ...

Viscosity Dependence Of Faraday Wave Formation Thresholds, 2014 California Polytechnic State University

#### Viscosity Dependence Of Faraday Wave Formation Thresholds, Lisa M. Slaughter

*Symposium*

This experiment uses an electromagnetic shaker to produce standing wave patterns on the surface of a vertically oscillating sample of silicon liquid. These surface waves, known as Faraday waves, form shapes such as squares, lines, and hexagons. They are known to be dependent upon the frequency and amplitude of the forcing as well as on the viscosity and depth of the liquid in the dish. At a depth of 4mm and for various silicon liquids having kinematic viscosities of 10, 20, and 38 cSt, we determined the acceleration at which patterns form for frequencies between 10 and 60 Hz. For ...

Modeling The Field Control Of The Surface Electroclinic Effect And Its Impact On Smectic Layer Strain, 2014 California Polytechnic State University - San Luis Obispo

#### Modeling The Field Control Of The Surface Electroclinic Effect And Its Impact On Smectic Layer Strain, Kara M. Zappitelli

*Physics*

Chiral, smectic liquid crystal molecules align in layers and can be controlled by the application of an electric field, yielding a variety of implications for the quality of liquid crystal (LC) displays. Both the bulk electroclinic effect (BECE) and surface electroclinic effect (SECE) impact the angle at which the molecules tilt with respect to the layer normal in different areas of a LC cell due to dipole interactions. Certain LC’s exhibit a continuous Sm-A* to Sm-C* transition, where the angles of the surface and bulk molecules change continuously with electric field strength. Other LC’s exhibit first order transitions ...

Onset Of Synchronization In The Disordered Hamiltonian Mean-Field Model, 2014 University of Colorado Boulder

#### Onset Of Synchronization In The Disordered Hamiltonian Mean-Field Model, James Meiss, Juan G. Restrepo

*Applied Mathematics Faculty Contributions*

We study the Hamiltonian mean field (HMF) model of coupled Hamiltonian rotors with a heterogeneous distribution of moments of inertia and coupling strengths. We show that when the parameters of the rotors are heterogeneous, finite-size fluctuations can greatly modify the coupling strength at which the incoherent state loses stability by inducing correlations between the momenta and parameters of the rotors. When the distribution of initial frequencies of the oscillators is sufficiently narrow, an analytical expression for the modification in critical coupling strength is obtained that confirms numerical simulations. We find that heterogeneity in the moments of inertia tends to stabilize ...

Morphology Characterization Of Low Band Gap Polymer-Based Organic Photovoltaics, 2014 University of Massachusetts Amherst

#### Morphology Characterization Of Low Band Gap Polymer-Based Organic Photovoltaics, Feng Liu

*Doctoral Dissertations*

In bulk heterojunction (BHJ) thin film organic photovoltaics (OPV), morphology control is critical to obtain good device efficiency. Nanoscale phase separation that creates bicontinuous interpenetrating structure on a size scale commensurate with exciton diffusion length (~10 nm) is thought to be the ideal morphology. Results obtained from this work indicate that morphology can be affected by chemical structure of the polymer, processing conditions, blending ratio and post treatments. Physical properties of the material, such as crystallinity, crystal orientation, material interactions and miscibility, surface energy and particle aggregations are critical for determining the morphology and thus the device performance. Previous investigations ...