Engineering Commons^™

Investigating The Rheological Behavior Of A Simple Yield Stress Fluid Under Shear Flows, Francesco Accetta

Theses

Many soft materials display unique and complex rheological behavior characterized by a transition from a solid-like to a fluid-like state upon the application of a force that exceeds the threshold to flow, known as the yield stress. Yield stress fluids are found in a wide range of commonly encountered materials including microgels, emulsions, and foams, and have been widely studied by rheologists over the last several decades. Carbopol is a popular polymeric microgel system as it displays simple, non-thixotropic rheological behavior and is typically seen as an ideal yield stress fluid. Previous research has demonstrated the reproducible behavior of shear …

Hydrodynamic Investigation Of The Discharge Of Complex Fluids From Dispensing Bottles Using Experimental And Computational Approaches, Baran Teoman

Dissertations

The discharge of non-Newtonian, complex fluids through orifices of industrial tanks, pipes, dispensers, or packaging containers is a ubiquitous but often problematic process because of the complex rheology of such fluids and the geometry of the containers. This, in turn, reduces the discharge rate and results in residual fluid left in the container, often referred to as heel. Heel formation is undesired in general, since it causes loss of valuable material, container fouling, and cross-contamination between batches. Heel may be of significant concern not only in industrial vessels but also in consumer packaging. Despite its relevance, the research in this …

Electric-Field Assisted Manipulation And Self-Assembly Of Particle Suspensions, Edison Chijioke Amah

Dissertations

The aim of this dissertation is to model the processes by which particles suspended in liquids and at liquid surfaces self-assemble when they are subjected to uniform and non-uniform electric fields. To understand the role of electric forces, three related problems were studied numerically and experimentally.

In the first problem, particles are assumed to be suspended inside a liquid and a nonuniform electric field is applied using electrodes mounted in the domain walls which causes positively polarized particles to collect in the regions where the electric field intensity is locally maximal and the negatively polarized particles collect in the regions …

Hot-Melt Mixing Of Partially Miscible Active Pharmaceutical Ingredient-Polymer Mixtures, Min Yang

Dissertations

Solid dispersion/solution processes for producing pharmaceutical oral dosages such as hot-met extrusion (HME) have received increasing attention by industry and academe because they can enhance drugs’ solubility and even bioavailability to a great extent by converting drugs from crystalline to amorphous form. HME can be carried out at two process temperature regimes: one where T_process > T_m of the drug and the T_g of the polymer (or the T_m for the case of semi-crystalline polymers); the other at T_m > T_process > T_g (T_m for the case of semi-crystalline polymer). Processing below the drug’s …

Reactive Modification And Crystallization Behavior Of Foamed Poly(Butylene Terephthalate), Byeong Joon Jeong

Dissertations

The objective of this study is to investigate the feasibility of preparing low density foams based on poly(butylene terephthalate) (PBT) through modification of its molecular structure and rheological characteristics by reactive extrusion. The scientific and/or engineering interpretation of the experimental data was based on fundamentals of extrusion, crystallization mechanisms, as well as information on reactivity and tendency toward degradation of PBT.

As a preliminary study, the extrusion foaming behavior of a commercial linear semi-crystalline PBT with a chemical blowing agent (CBA) was investigated. Foam characteristics were functions of extrusion operational variables, such as die set temperature and screw speed. Gas …

Rheo-Optical Properties Of Polyisobutylene, Russell B. Biss

Theses

This study presents quantitative experimental data on the various stress-optical characteristics of polymer liquids, specifically, polyisobutylene. Through the use of a concentric cylinder rheogoniometer and a rotational viscometer, the temperature effects of a newtonian polyisobutylene liquid. was studied and was found to have a stress-optical coefficient independent of shear stress and minor temperature changes. The experiments confirm that the birefringence is a known function of the extinction angle and the shear stress. Various polyisobutylene liquids were used in a simple flow device to observe the birefringence in the 1-3 plane and the 2-3 plane. The results indicate that the 1-3 …

The Application Of A Non-Newtonian Rheological Equation To Low-Density Polyethylene, Jeffrey N. Goldstein

Theses

A generalized non-Newtonian equation describing the rheology of molten thermoplastics is verified for low-density polyethylenes. The equation is extended to account for both rheological temperature dependency and polyethylene molecular weight dependency. The prediction of the rheology of new polyethylenes without additional experimentation is thus possible.