Mechanical & Materials Engineering, Department of
First Advisor
Yuris Dzenis
Second Advisor
Nicolas Delpouve
Third Advisor
Li Tan
Date of this Version
11-2023
Citation
A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science
Major: Mechanical Engineering and Applied Mechanics
Under the supervision of Professor Yuris Dzenis
Lincoln, Nebraska, December 2023
Abstract
This thesis presents a study on the properties of Bombyx Mori silk nanofibers and polyimide (PI) nanofibers. Firstly, a Bombyx Mori silk solution has been created with degummed silkworm cocoons in order to separate the fibroin and the sericin, the two main proteins of the silk. The fibroin was then centrifuged to remove insoluble particles and stored and 4°C before mixing with hexafluoroisopropanol (HFIP). On the second part, a polyimide solution, made with shavings of polyimide and N,N-dimethylformamide (DMF). Both solutions are then electrospun. Electrospinning parameters are studied. In this way, a part of my thesis has been dedicated to this point. The objective of this thesis is, then, to study size effects on the structure of nanofibers by investigating two different systems that could be used as matrix reinforcement for various applications: a biological (silk) macromolecule and a synthetic (polyimide) polymer. During my first year, I managed electrospinning itself and started the investigation of their physical properties. Following the electrospinning process, the nanofiber characterization has been performed thanks to thermal and Raman analysis, as well as some mechanical testing. For silk nanofibers, a range between 1.2% and 6% of silk in the solution was used for electrospinning. Following similar ideas, I used between 9% and 12% of polyimide to prevent the solution being viscous and useless. Then, the fibers were observed by microscopy with Scanning Electron Microscopy (SEM) to see their structure, their uniformity and their average diameter. Mechanical properties of PI have been studied thanks to a drawing system, in order to calculate the stress as a function of deformation with a machine called NanoUTM. During my second year, I performed complementary Differential Scanning Calorimetry (DSC) analyses to evidence their crystalline structure and their characteristic temperatures. Besides, some spectroscopical experiments have been done with XRD, allowing us to get additional information to those brought by Raman spectroscopy.
Additional synopsis: This work is about electrospinning properties on silk and polyimide nanofibers. The goal is to compare those fibers as a natural and a synthetic polymer with mechanical, thermal and spectroscopical analysis.
Advisor: Yuris Dzenis
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Copyright 2023, Sabrina Leseul