Date of Award

Summer 2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Chester Wilson

Abstract

With the rapid advancement of additive manufacturing technologies in recent years on both the microscale and the macroscale, research must be done to test the limits of currently available technologies. On the microscale, halloysite nanotubes have proven to be a viable platform for reinforcement of polymers and time release of loaded chemicals, as well as a substrate material for the deposition of nanoparticles. The range of materials are limited due to polarity conflicts, and often lead to wet chemical processes that use more toxic alternatives. Three-dimensional (3D) printing and macroscale additive manufacturing techniques can be used to generate custom structures, however introduction of additives is a difficult proposition without access to industrial scale equipment. Dopants in the form of nanoparticles show great promise for achieving desired properties. Combinations of the technologies can be used in such applications as targeted treatments in medical research, complex geometrical radiation shielding, and printing and casting of conductive structures for a wide array of use.

In this work, halloysite nanotubes were investigated as a platform for the dry deposition of metallic nanoparticles through sintering of metal acetylacetonate and metal acetate compounds. These coatings were solely or in combinations achieved for iron, nickel, copper, barium, lithium, and gold. Targeted characterization was performed on the iron, barium, gold, and iron/gold dual coated halloysite to quantify exhibited characteristics of the achieved coatings: magnetic susceptibility of the iron coating, X-ray contrast of the barium coating, and laser resonance with 532 nm and 808 nm wavelengths for the iron, gold, and iron/gold coatings.

A process for fabricating metal doped 3D printing filaments was invented using commercially available equipment and designed to allow for the shielding of low level radiation printed to a user designed specification. Metals used include iron oxide and barium sulfate. Printed films utilizing the iron oxide doped filament were shown to have a dopant threshold through the discovered method of 25wt% and showed an increase in beta radiation shielding of twice that of undoped PLA. Barium sulfate was likewise found to have a 25wt% doping threshold and showed successive increases in opacity when tested against clinical medical X-ray machines.

Conductive 3D printing filaments were also manufactured without modification of equipment, and the electrical characteristics of printed structures were measured in an attempt to classify the use of such a fabrication method for the manufacture of a hybrid conductive/nonconductive structure with attributes defined by the user. It was found that through the method used, conductive filaments using 15-20wt% graphene could be fabricated. Below this threshold, the material proved insulating; above this threshold, filament extrusion was inhibited. Resistances were found to be 1.5±0.4 MΩ and 60±7 kΩ for the 15 and 20 wt% filaments, respectively. Further, notable junction capacitances on the order of 20 pF were found for the 20wt% due to the charge accumulation around air voids inherent in the printing process. No notable junction capacitances were found for the 15wt%. Conductive bone cements were also manufactured to test the impact of the addition of graphene to the manufacturing process. Body resistance testing showed uneven dispersion through normal manufacturing means, and flexural testing showed varied electrical characteristics depending upon the doping percentage. Mechanical properties were also found to be inhibited at doping percentages greater than 10wt%, however these could be overcome through the use of greater MMA monomer in the manufacturing process.

The first ever ability to coat halloysite nanotubes through a dry sintering process was developed as a proof of principle for multi-functional and real time customizable nanoparticle platforms. Likewise, a method to create and use metal doped and conductive 3D printing filaments on the tabletop scale was realized. Conductive bone cements were also manufactured to test their applicability as a sensor platform. Nanoparticles as additives showed ways to modify these nanotubes or 3D printing filaments with enhanced features and properties easily tailored to desired specifications.

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