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Articles 1 - 9 of 9
Full-Text Articles in Engineering
Effects Of Polymer-Nanoparticle Interactions On The Dynamics Of Attractive Polyhedral Oligomeric Silsesquioxane Nanocomposites, Walter W. Young
Effects Of Polymer-Nanoparticle Interactions On The Dynamics Of Attractive Polyhedral Oligomeric Silsesquioxane Nanocomposites, Walter W. Young
Doctoral Dissertations
Polyhedral oligomeric silsesquioxane (POSS) had long been recognized as a critical building block for inorganic-organic hybrid materials with unique and desirable properties and performance. Through synthesis and characterization of polymer/POSS nanocomposites, direct insights into the significant effects of the polymer/POSS interactions on the resulting material properties are obtained. Random copolymers of a hydrogen-bond accepting monomer and a non-interacting monomer are synthesized and loaded with a model amine-functionalized hydrogen bond donating POSS molecule via solution casting, to create a material with well-controlled dynamical heterogeneity. The increase in the glass transition temperature (Tg) of these materials is found to strongly depend on …
Theory And Improved Methods For Probing The Cavitation To Fracture Transition, Christopher Barney
Theory And Improved Methods For Probing The Cavitation To Fracture Transition, Christopher Barney
Doctoral Dissertations
A material is considered soft when its bulk modulus is significantly greater than its shear modulus. Rubbery polymers are a class of soft materials where resistance to extension is mainly entropic in nature. Polymeric soft solids differ from liquids due to the presence of a percolated network of strong bonds that resist deformation and flow on a given time scale. The incompressible nature, entropically driven elasticity, and molecular scale network structure of soft polymeric solids combine to impart unique mechanical behavior that often results in complex material responses to simple loading situations. An important example of this is cavitation in …
Amorphous-Crystalline Brush Block Copolymers: Phase Behavior, Rheology And Composite Design, Gayathri Kopanati
Amorphous-Crystalline Brush Block Copolymers: Phase Behavior, Rheology And Composite Design, Gayathri Kopanati
Doctoral Dissertations
Bottlebrush block copolymers are polymers with chemically distinct polymer side chains grafted onto a common backbone. The unique architecture induced properties make these materials attractive for applications such as photonic materials, stimuli responsive actuators and drug delivery vehicles to name a few. This dissertation primarily investigates the phase transitions and rheological behavior of amorphous-crystalline bottlebrush brush block copolymers and their composites. The temperature induced phase behavior is investigated using time resolved synchrotron X-ray source. Irrespective of volume fraction and backbone length, the samples display strong segregation even at high temperatures (200 °C) and there is no accessible order-disorder transition in …
Rheological Properties Of A Model Soft Solid Nanocomposite, Vijesh Tanna
Rheological Properties Of A Model Soft Solid Nanocomposite, Vijesh Tanna
Doctoral Dissertations
ABSTRACT RHEOLOGICAL PROPERTIES OF A MODEL SOFT SOLID NANOCOMPOSITE SEPTEMBER 2018 VIJESH A. TANNA B.S. UNIVERSITY OF ILLINOIS URBANA-CHAMPAIGN M.S. UNIVERSITY OF MASSACHUSETTS AMHERST Ph.D. UNIVERSITY OF MASSACHUSETTS AMHERST Directed by: Prof. H. Henning Winter The fabrication and physical properties of polymer/clay nanocomposites has received a great deal of interest in both academic and industrial settings. Clay is a natural 2D mineral comprised of stacks of platelets with high aspect ratios held together through electrostatic interactions. Typically, polymer/clay composite are found to have the best physical properties when these clay sheets are randomly dispersed, exfoliated, throughout the polymer matrix. However, …
Experimental And Modeling Studies On The Formulation Of Stable Lipid Nanoparticle Dispersions, Yihui Yang
Experimental And Modeling Studies On The Formulation Of Stable Lipid Nanoparticle Dispersions, Yihui Yang
Doctoral Dissertations
This thesis presents both experimental and modeling studies on the formulation of stable lipid nanoparticle dispersions. A population balance equation (PBE) model was developed for prediction of the average polymorph content and aggregate size distribution to better understand the undesirable SLN aggregation behavior. Experimental and modeling studies showed that the polymorphic transformation was the rate determining step for my system, SLNs with smaller initial size distributions aggregated more rapidly, and aggregates contained particles with both alpha and beta crystals. Next the effect of different liquid carrier oils on the crystallization and aggregation behavior of tristearin NLC dispersions was investigated. I …
Strategies For Improving Oxygen Transport And Mechanical Strength In Alginate-Based Hydrogels, Joseph C. White
Strategies For Improving Oxygen Transport And Mechanical Strength In Alginate-Based Hydrogels, Joseph C. White
Doctoral Dissertations
Hydrogels have attracted significant interest over the past several decades due to their outstanding versatility as biomaterials. Alginate-based hydrogels are among the most popular studied due to their low cost, biocompatibility, and tunable physical properties. However, as with all hydrogels, persistent oxygen solubility and poor mechanical strength limits their utility for creating macroscopic devices for biomedical use. This thesis presents two strategies for improving oxygen transport and mechanical properties of alginate-based hydrogel. The former involves incorporating perfluorocarbons, hydrophobic compounds with very high oxygen solubility, into the formulation. The perfluorocarbons are stabilized by nonionic surfactants, Pluronics®, and the emulsion is entrapped …
Fiber Formation From The Melting Of Free-Standing Polystyrene, Ultra-Thin Films: A Technique For The Investication Of Thin Film Dynamics, Confinement Effects And Fiber-Based Sensing, Jeremy M. Rathfon
Open Access Dissertations
Free-standing ultra-thin films and micro to nanoscale fibers offer a unique geometry in which to study the dynamics of thin film stability and polymer chain dynamics. By melting these films and investigating the subsequent processes of hole formation and growth, and fiber thinning and breakup, many interesting phenomena can be explored, including the nucleation of holes, shear-thinning during hole formation, finite-extensibility of capillary thinning viscoelastic fibers, and confinement effects on entanglement of polymer chains. Free-standing films in the melt are unstable and rupture due to instabilities. The mechanism of membrane failure and hole nucleation is modeled using an energy barrier …
Structure-Property Evolution During Polymer Crystallization, Deepak Arora
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 …
Water-In-Oil Microemulsions: Counterion Effects In Aot Systems And New Fluorocarbon-Based Microemulsion Gels, Xiaoming Pan
Water-In-Oil Microemulsions: Counterion Effects In Aot Systems And New Fluorocarbon-Based Microemulsion Gels, Xiaoming Pan
Open Access Dissertations
Microemulsions have important applications in various industries, including enhanced oil recovery, reactions, separations, drug delivery, cosmetics and foods. We investigated two different kinds of water-in-oil microemulsion systems, AOT (bis(2-ethylhexyl) sulfosuccinate) microemulsions with various counterions and perfluorocarbon-based microemulsion gels with triblock copolymers. In the AOT systems, we investigated the viscosity and interdroplet interactions in Ca(AOT)2, Mg(AOT)2 and KAOT microemulsions, and compared our results with the commonly-studied NaAOT/water/decane system. We attribute the differences in behavior to different hydration characteristics of the counterions, and we believe that the results are consistent with a previously proposed charge fluctuation model. Perfluorocarbons (PFCs) are of interest …