Date of Award

Fall 2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical Engineering

First Advisor

Boris Khusid

Second Advisor

Rajesh N. Dave

Third Advisor

Robert Pfeffer

Fourth Advisor

Edward L. Dreyzin

Fifth Advisor

Mirko Schoenitz

Abstract

Jet breakup phenomenon and nanoparticle formation

The focus of this dissertation is to study the SAS process to manufacture nanoparticles with minimum agglomeration, controlled size and size distribution. Solution jet breakup and solvent evaporation into supercritical fluid (SC CO2) is studied using high speed charged coupled device (CCD) camera facilitated with double shot particle image veloimetry (PIV) laser and a high pressure view cell. Particles formation using SAS is studied. Polyvinylpyrrolidone (PVP) particles are formed using micron size capillary nozzles and combination of thermodynamically good and poor solvents in order to achieve nano-sized particles with reduced agglomeration and narrow size distribution. Effects of operational parameters on physiochemical properties of particles are investigated. Since the proposed method is based on general thermodynamic properties of polymer-solvent systems, it should be applicable to a wide variety of polymers for applications ranging from the improvement of the flow and packing properties of powders to the control of particle interaction with their external surroundings for drug delivery systems.

Fine particle coating and encapsulations using supercritical fluids.

In certain applications, particle surfaces need to be modified or functionalized by coating them with another material to serve a specific purpose. As nanoparticles are extremely cohesive, it is very difficult to coat an individual particle by traditional methods. In this research, nanoparticles coating is investigated through supercritical fluid-based methods. Agglomeration of particles is reduced by combining poor solvent and ultrasonic techniques. The first technique uses a proprietary co-axial ultrasonic nozzle to spray the solution suspension into the SC CO2. Ultrasound is very effective in breaking agglomerates, and the introduction of the co-axial flow enables CO2 to not only serve as an antisolvent, but also as a mixing enhancer. The second technique uses a combination of thermodynamically good and poor solvents to tune the supersaturation of the polymer which serves as the coating material. Other methods like raid expansion of supercritical solution (RESS) and particles from gas saturated solution (PGSS) are also investigated and compared with SAS.

Syneresis of silica gel

Effects of gravity, silica concentration in gel and time on syneresis are studied by exposing the simulants of gel propellants to higher gravities. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) are used to characterize the gel. Based on results of experimental studies, a multi-scale computational strategy for modeling gel formation and syneresis is proposed. Based on the analysis of the existing literature, directions for experimental and theoretical approaches for particles formation and coating are proposed, and form the main parts of this thesis. This summary section outlines the major components of proposed research; first, important features of the nanoparticles formation using SAS techniques are discussed followed by the nanocoatings and finally syneresis of silica gels.

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