Engineering Commons^™

Bending, Wrinkling, And Folding Of Thin Polymer Film/Elastomer Interfaces, Yuri Ebata

Open Access Dissertations

This work focuses on understanding the buckling deformation mechanisms of bending, wrinkling, and folding that occur on the surfaces and interfaces of polymer systems. We gained fundamental insight into the formation mechanism of these buckled structures for thin glassy films placed on an elastomeric substrate. By taking advantage of geometric confinement, we demonstrated new strategies in controlling wrinkling morphologies. We were able to achieve surfaces with controlled patterned structures which will have a broad impact in optical, adhesive, microelectronics, and microfluidics applications.

Wrinkles and strain localized features, such as delaminations and folds, are observed in many natural systems and are …

Scaling Reversible Adhesion In Synthetic And Biological Systems, Michael David Bartlett

Open Access Dissertations

Geckos and other insects have fascinated scientists and casual observers with their ability to effortlessly climb up walls and across ceilings. This capability has inspired high capacity, easy release synthetic adhesives, which have focused on mimicking the fibrillar features found on the foot pads of these climbing organisms. However, without a fundamental framework that connects biological and synthetic adhesives from nanoscopic to macroscopic features, synthetic mimics have failed to perform favorably at large contact areas. In this thesis, we present a scaling approach which leads to an understanding of reversible adhesion in both synthetic and biological systems over multiple length …

Computer Simulation Of Viral-Assembly And Translocation, Jyoti Prakash Mahalik

Open Access Dissertations

We investigated four different problems using coarse grained computational models : self-assembly of single stranded (ss) DNA virus, ejection dynamics of double stranded(ds) DNA from phages, translocation of ssDNA through MspA protein pore, and segmental dynamics of a polymer translocating through a synthetic nanopore. In the first part of the project, we investigated the self-assembly of a virus with and without its genome. A coarse-grained model was proposed for the viral subunit proteins and its genome (ssDNA). Langevin dynamics simulation, and replica exchange method were used to determine the kinetics and energetics of the self-assembly process, respectively. The self-assembly follows …

Solution Assembly Of Conjugated Polymers, Felicia Bokel

Open Access Dissertations

This dissertation focuses on the solution-state polymer assembly of conjugated polymers with specific attention to nano- and molecular-scale morphology. Understanding how to control these structures holds potential for applications in polymer-based electronics. Optimization of conjugated polymer morphology was performed with three objectives: 1) segregation of donor and acceptor materials on the nanometer length-scale, 2) achieving molecular-scale ordering in terms of crystallinity within distinct domains, and 3) maximizing the number and quality of well-defined donor/acceptor interfaces.

Chapter 1 introduces the development of a mixed solvent method to create crystalline poly(3-hexyl thiophene) (P3HT) fibrils in solution. Chapter 2 describes fibril purification and …

Photo-Reaction Of Copolymers With Pendent Benzophenone, Scott Kenneth Christensen

Open Access Dissertations

This dissertation aims to both deepen and broaden our understanding of copolymers with pendent benzophenone (BP) in relation to both established applications and novel directions in materials science. Photo-reaction of these BP copolymers is explored in attempts to achieve three distinct goals: (1) robust and efficiently photo-crosslinkable solid polymer films, (2) photo-reacted polymer blends with disordered bicontinuous nanostructures, and (3) photo-patterned hydrogel materials with environmental UV stability. We begin by investigating the fundamental gelation behavior of solid polymer films, finding BP copolymers to be particularly effective crosslinkable materials. Gelation efficiency can be tuned according to comonomer chemistry, as BP hydrogen …

Particle Behavior On Anisotropically Curved Interfaces, Kathleen Mcennis

Open Access Dissertations

This dissertation presents experimental research investigating the behavior of particles on two different types of anisotropically curved liquid interfaces: cylinders and catenoids. The results are compared to the behavior predicted by theoretical models. Several types of liquids and many types of particles were examined. The size scale of the surfaces ranges from microns to millimeters, with nanometer and micron sized particles.

Semi-cylinders, a few hundred microns in diameter, were made by creating a line of liquid on a surface. Three different fluids were used to create the semi-cylinders: Gallium, ionic liquids, and molten polystyrene (PS). Particle behavior on semi-cylinder liquid …

Characterization Of Self-Assembled Functional Polymeric Nanostructures: I. Magnetic Nanostructures From Metallopolymers Ii. Zwitterionic Polymer Vesicles In Ionic Liquid, Raghavendra Raj Maddikeri

Open Access Dissertations

Two diverse projects illustrate the application of various materials characterization techniques to investigate the structure and properties of nanostructured functional materials formed in both bulk as well as in solutions. In the first project, ordered magnetic nanostructures were formed within polymer matrix by novel metallopolymers. The novel metal-functionalized block copolymers (BCPs) enabled the confinement of cobalt metal ions within nanostructured BCP domains, which upon simple heat treatment resulted in room temperature ferromagnetic (RTFM) materials. On the contrary, cobalt functionalized homopolymer having similar chemical structure and higher loading of metal-ion are unstructured and exhibited superparamagnetic (SPM) behavior at room temperature. Based …

Helical Ordering In Chiral Block Copolymers, Wei Zhao

Open Access Dissertations

The phase behavior of chiral block copolymers (BCPs*), namely, BCPs with at least one of the constituent block is formed by chiral monomers, is studied both experimentally and theoretically. Specifically, the formation of a unique morphology with helical sense, the H* phase, where the chiral block forms nanohelices hexagonally embedded in the matrix of achiral block, is investigated. Such unique morphology was first observed in the cast film of polystyrene-b-poly(L-lactide) (PS-b-PLLA) from a neutral solvent dichloromethane at room temperature with all the nanohelices being left-handed, which would switch to right-handed if the PLLA block changes to …

Macroscopic Patterning Via Dynamic Self-Assembly And Wrinkling Instability, Hyun Suk Kim

Open Access Dissertations

My PhD work focuses on developing new methods to create the macroscopic patterns in a simple, robust, and versatile way. For macroscopic pattern formation, we first use flow coating as an assembly technique, uniquely balancing two driving forces: (i) evaporative deposition of nonvolatile solutes at a three-phase contact line and (ii) precision movement of a confined meniscus layer. This balance leads to the formation of line-based patterns that range in height and width from nanometers to microns, with lengths greater than centimeters. Moreover, we couple this deposition methodology with functional ligand chemistry on the nanoparticle surface, which allows us to …

Porous Metal Oxide Materials Through Novel Fabrication Procedures, Nicholas Hendricks

Open Access Dissertations

Porous metal oxide materials, particularly those comprised of silica or titania, find use in many applications such as low-k dielectric materials for microelectronics as well as chemical sensors, micro/nanofluidic devices, and catalyst substrates. For this dissertation, the focus will be on the processing of porous metal oxide materials covering two subjects: hierarchical porosity exhibited over two discrete length scales and incorporation of functional nanomaterials. To generate the porous silica materials, the technique of supercritical carbon dioxide infusion (scCO2) processing was heavily relied upon. Briefly, the scCO2 infusion processing utilizes phase selective chemistries within a pre-organized amphiphilic block copolymer template using …

Interactions And Morphology Of Triblock Copolymer - Ionic Liquid Mixtures And Applications For Gel Polymer Electrolytes, Daniel F. Miranda

Open Access Dissertations

Room temperature ionic liquids (ILs) are a unique class of solvents which are characterized by non-volatility, non-flammability, electrochemical stability and high ionic conductivity. These properties are highly desirable for ion-conducting electrolytes, and much work has focused on realizing their application in practical devices. In addition, hydrophilic and ionophilic polymers are generally miscible with ILs. The miscibility of ILs with ion-coordinating polymers makes ILs effective plasticizers for gel polymer electrolytes. Due to their unique properties, ILs present a means to realize the next generation of energy storage technology. In this dissertation, the fundamental interactions between poly(ethylene oxide) (PEO) and a variety …

Chemistry At Silicone - Inorganic Oxide Interfaces, Joseph W. Krumpfer

Open Access Dissertations

This dissertation describes research performed using siloxane polymers. This includes the reactions of siloxane polymers with inorganic oxide surfaces to form covalently attached monolayers, and the electrical properties of crosslinked silicone composite films fabricated by compounding with nickel particles. In addition to these topics, the use of contact line pinning as a practical and controllable method for the deposition of materials on superhydrophobic and chemically patterned surfaces is also described The first chapter provides a general review of siloxane polymer chemistry, focusing in particular on the relationship between molecular structure and physical properties. The use and fabrication of silicone composite …

Systematic Synthesis Of Organic Semiconductors With Variable Band Gaps, Christopher Thomas Scilla

Open Access Dissertations

Polymeric materials are attractive candidates for the fabrication of low cost, large area photovoltaic devices. Controlling the band gap of the electroactive polymer is an essential factor in optimizing the resulting devices. In this dissertation, a methodology for the synthesis of well-defined semiconducting materials with tunable band gaps is described. First, the synthesis, characterization, and computational analysis of a variety of trimers consisting of two 3-hexylthiophene units flanking a central moiety consisting of thiophene, or one of the electron donating monomers isothianaphthene or thieno[3,4,b]thiophene will be described. From this analysis the influences of the electronic and steric structure of the …

Kinetically Trapping Co-Continuous Morphologies In Polymer Blends And Composites, Le Li

Open Access Dissertations

Co-continuous structures generated from the phase separation of polymer blends present many opportunities for practical application. Due to the large interfacial area in such structures and the incompatibility between the components, such non-equilibrium structures tend to coarsen spontaneously into larger sizes and eventually form dispersed morphologies. Here, we utilize various strategies to kinetically stabilize the co-continuous structures in polymer blend systems at nano- to micro- size scales.

In the partially miscible blend of polystyrene and poly(vinyl methyl ether), we took advantage of the spinodal decomposition (SD) process upon thermal quenching, and arrested the co-continuous micro-structures by the addition of nanoparticles. …

Mechanical Evaluation Methods For Polymer And Composite Systems, Donna Theresa Wrublewski

Open Access Dissertations

This dissertation describes the development and application of various mechanical characterization techniques to four types of polymer composite materials. The composite nature of these materials ranges from molecular to macro-scale, as do the size scales probed by the techniques chosen. The two main goals of this work are to evaluate the suitability of existing characterization methods to new composite materials (and augment the methods as needed), and to use these methods to determine optimal composite system parameters to maximize the desired mechanical response. Chapter 2 employs nondestructive ultrasonic spectroscopy for characterizing the stiffness response of both micron-scale woven composites and …

Structure-Property Evolution During Polymer Crystallization, Deepak Arora

Open Access Dissertations

The main theme of this research is to understand the structure-property evolution during crystallization of a semicrystalline thermoplastic polymer. A combination of techniques including rheology, small angle light scattering, differential scanning calorimetry and optical microscopy are applied to follow the mechanical and optical properties along with crystallinity and the morphology. Isothermal crystallization experiments on isotactic poly-1-butene at early stages of spherulite growth provide quantitative information about nucleation density, volume fraction of spherulites and their crystallinity, and the mechanism of connecting into a sample spanning structure. Optical microscopy near the fluid-to-solid transition suggests that the transition, as determined by time-resolved mechanical …

Diffusion And Structure In Complex Fluids: I. Axial Diffusion In Membranes Ii. Proteins In Ionic Liquids, Malvika Bihari

Open Access Dissertations

Geometrically hindered motions of a single large solute (particle or polymer) can be imaged in real time via optical microscopy. The dynamics of fluorescent colloidal particles near surfaces and in porous membranes were monitored using confocal microscopy. A method of analysis to estimate diffusivity of particles in the axial direction by observing their intensity fluctuations was developed. The intensity fluctuations correspond to the Brownian motion of the particles in the axial direction. The method was successful in capturing the hindered diffusion of particles close to surfaces and in pores. This study provides a novel route to monitor the dynamics of …

Polymer Composites And Porous Materials Prepared By Thermally Induced Phase Separation And Polymer-Metal Hybrid Methods, Joonsung Yoon

Open Access Dissertations

The primary objective of this research is to investigate the morphological and mechanical properties of composite materials and porous materials prepared by thermally induced phase separation. High melting crystallizable diluents were mixed with polymers so that the phase separation would be induced by the solidification of the diluents upon cooling. Theoretical phase diagrams were calculated using Flory-Huggins solution thermodynamics which show good agreement with the experimental results. Porous materials were prepared by the extraction of the crystallized diluents after cooling the mixtures (hexamethylbenzene/polyethylene and pyrene/polyethylene). Anisotropic structures show strong dependence on the identity of the diluents and the composition of …

Synthesis And Study Of Hybrid Organic – Inorganic Polyhedral Oligomeric Silsesquioxanes (Poss) Based Polymers, Gunjan A, Gadodia

Open Access Dissertations

Hybrid organic-inorganic materials represent a new class of materials having scientific and technological potential. In this thesis, Polyhedral Oligomeric Silsesquioxanes (POSS) are used as an inorganic building block which has been tethered to an organic polymer. POSS are silica precusors, having a well defined silsesquioxane cental core surrounded by an organic periphery which makes them compatible with monomers and possibly polymers. The objectives of this study are to (1) study the basic structures of POSS homopolymers, (2) to incorporate POSS building blocks by a bottomup approach into polymer chains and study the resulting morphologies, and (3) to study the thin …

Developing Reactive Molecular Dynamics For Understanding Polymer Chemical Kinetics, Kenneth D. Smith

Open Access Dissertations

One of the challenges in understanding polymer flammability is the lack of information about microscopic events that lead to macroscopically observed species, and Reactive Molecular Dynamics is a promising approach to obtain this crucially needed information. The development of a predictive method for condensed-phase reaction kinetics can provide significant insight into polymer ammability, thus helping guide future synthesis of fire-resistant polymers. Through this dissertation, a new reactive forcefield, RMDff, and Reactive Molecular Dynamics program, RxnMD, have been developed and used to simulate such material chemistry. It is necessary to have accurate description of chemical kinetics to describe quantitative chemical kinetics. …