Date of Award

2017-01-01

Degree Name

Master of Science

Department

Metallurgical and Materials Engineering

Advisor(s)

Anupama B. Kaul

Abstract

This project was multipronged to help fuse together topics of additive manufacturing and two-dimensional (2D) layered materials, and studying the mechanical and electrical properties of the composites produced. The composites are made from the thermoplastic polymer acting as a matrix and the graphite and 2D transition metal dichalcogenides (TMDs) serving as the filler or reinforcement. Different concentrations of TMD's were added to the matrix to study the effect of composition on the mechanical and electrical properties. To shed insights into the mechanical properties, test coupons were produced as "dog bone" structures for tensile testing using the ASTM D638 type 5 standard, which were printed with the aid of a Lulzbot TAZ 6 3D printer. In the same way, two-terminal resistor-like structures were printed to test the electrical properties inherent to the composites.

From the measurements conducted, polyethylene terephthalate glycol (PETG)—graphite composites had a yield strength (YS) ≈ 50 MPa, an ultimate tensile strength (UTS) ≈ 30 MPa and had a better ductility (strain to rupture ≈ 8%) compared to theacrylonitrile butadiene styrene (ABS) composite counterparts. Also, molybdenum disulfide (MoS2) had a more positive effect than tungsten disulfide (WS2), since the strength was retained while the ductility was increased at low loadings of the material. Strain levels were measured to be 30%–120% when adding 1 wt% of MoS2 and WS2. On the other hand, with high additions of MoS2 and WS2 (15 and 20 wt%) ductility was completely lost since no plastic deformation occurred during the testing. Moreover, PETG – graphite resistor-like structures were 3-dimensional (3D) printed and tested with the help of a semiconductor parameter analyzer. All samples were tested at different radius of curvatures (0 cm-1, 0.072 cm-1, 0.087 cm-1, 0.112 cm-1, 0.157 cm-1, and 0.262 cm -1) which showed a composite that was strain insensitive. The obtained average conductivity and resistivity were ≈ 5.27 Siemens-m-1 and 0.250 Ohm-m, respectively. In the process of forming the composites, some pretreatment of the 2D material may also be necessary. We studied one aspect of this pretreatment by looking at particle size measured using dynamic light scattering. The fragmentation rate (FR) of 2D MoS2, WS2, and graphite in N-methyl-pyrrolidinone (NMP) was computed in chemical exfoliants, where FR is a measure of the particle size reduction as a function of ultrasonication time. For the 2D layered materials, the highest FR generally occurred for sonication times tsonic = 30 min., after which point FR varied less sensitively with tsonic. The highest FR occurred for graphite, where FRGraphite was ~ -1176.4 µm-hr -1, while FRWS2 and FRMoS2 was measured to be ~ -32.4 µm-hr-1 and ~ -3.8 µm-hr-1, respectively. This pretreatment maybe an important step to further tune the properties of the hybrid organic-inorganic composites of 2D materials with polymeric systems for a number of application platforms.

Language

en

Provenance

Received from ProQuest

File Size

102 pages

File Format

application/pdf

Rights Holder

Jorge Alfredo Catalan Gonzalez

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