PhD Defense by Alex Lohse

Event Details
  • Date/Time:
    • Tuesday July 17, 2018
      10:30 am - 12:30 pm
  • Location: MRDC 3515
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    N/A
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Summaries

Summary Sentence: Structure-Property Linkage Evolution for Molecular Simulation of Polymeric Matrix Composites

Full Summary: No summary paragraph submitted.

THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

 

GEORGIA INSTITUTE OF TECHNOLOGY

 

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Tuesday, July 17, 2018

10:30 AM
in MRDC 3515

 

will be held the

 

DISSERTATION DEFENSE

for

 

Alex Lohse

 

"Structure-Property Linkage Evolution for Molecular Simulation of Polymeric Matrix Composites"

 

Committee Members:

 

Prof. Karl Jacob, Co-Advisor, MSE

Prof. Edmond Chow, Co-Advisor, CSE

Prof. Surya Kalidindi, MSE

Prof. Jerry Qi, ME

Prof. Donggang Yao, MSE

 

Abstract:

 

The use of composite materials has risen significantly over the past several decades as many industries begin to take advantage of the high specific strength, specific modulus, and tailorable mechanical properties that polymeric matrix composites can provide. However, the number of filler types, surface functionalities, and filler orientations in composites reinforced with nano and macroscale fillers leads to a complicated and lengthy trial and error experimental approach. Computational researchers have been trying to find a new approach to narrow down promising combinations of fillers and matrix materials using their known chemical and mechanical attributes. This work is directed toward developing structure-property linkages in a range of composite materials using molecular dynamics simulation. This research analyzed the (1) interphase atomistic structure of an epoxy/graphene system with different surface functionalities, (2) dissolution (recycling) mechanism and thermomechanical properties of covalent adaptable networks (CAN), and (3) reaction mechanism pathways and structure development for carbonization of polyacrylonitrile (PAN).

 

The first research area characterized epoxy interphase structure when graphene had non-covalent and covalent surface functionalities using 2-point spatial statistics and/or radial distribution functions. Principal component analysis was used to reduce the statistical representations of the interphase structure in epoxy to its most salient features and ordinary least-squares regression related the principal components to temperature changes during cooling through glass transition and stress values during simulated tensile strain. The models were able to predict bulk system temperature and

stress each with over 90% prediction accuracy. The second research area developed a classical molecular dynamics simulation methodology for bond exchange reactions and dissolution in covalent adaptable networks interacting with ethylene glycol solvent. Increasing the rate of bond exchange reactions was found to increase both dangling end intradiffusion and ethylene glycol interdiffusion. Bond exchange reactions were found to improve the solvent diffusivity when degree of crosslinking was over the gelation point. Under the gelation point the enhanced chain mobility from bond exchange reactions is negligible compared to the chain mobility as a result of a lightly crosslinked network. Thermomechanical properties of CANs with different crosslink densities were correlated to overall free volume and individual void shape calculations. The final research area used ReaxFF simulations to study detailed reaction mechanisms and structure development resulting from carbonization of stabilized polyacrylonitrile (s-PAN). Higher oxygen content fibers promoted formation of CO and CO2 gases which lowered the final fiber carbon content. Regardless of the initial molecular orientation of s-PAN, the carbonization process shifted the final graphitic structures toward a random orientation relative to the fiber axis. Higher temperature was found to significantly improve the numbers of graphite rings in the final structure. Detailed reaction mechanism analysis showed that H2 and N2 elimination produce carbon radicals that form crosslinks with other s-PAN molecules and lead to ring formation and fiber densification.

Additional Information

In Campus Calendar
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Graduate Studies

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Public, Graduate students, Undergraduate students
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Other/Miscellaneous
Keywords
Phd Defense
Status
  • Created By: Tatianna Richardson
  • Workflow Status: Published
  • Created On: Jul 6, 2018 - 2:51pm
  • Last Updated: Jul 6, 2018 - 2:51pm