Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Lacy, Thomas E.

Committee Member

Gwaltney, Steven R.

Committee Member

Pittman Jr., Charles U.

Committee Member

Toghiani, Hossein

Committee Member

Sullivan, Rani Warsi

Date of Degree

1-1-2012

Document Type

Dissertation - Open Access

Degree Name

Doctor of Philosophy

College

College of Engineering

Department

Department of Aerospace Engineering

Abstract

Molecular dynamics (MD) simulations have been performed to investigate the system equilibrium through the atomic/molecular interactions of a liquid vinyl ester (VE) thermoset resin with the idealized surfaces of both pristine vapor-grown carbon nanofibers (VGCNFs) and oxidized VGCNFs. The VE resin has a mole ratio of styrene to bisphenol-A-diglycidyl dimethacrylate VE monomers consistent with a commercially available 33 wt% styrene VE resin (Derakane 441-400). The VGCNF-VE resin interactions may influence the distribution of the liquid VE monomers in the system and the formation of an interphase region. Such an interphase may possess a different mole ratio of VE resin monomers at the vicinity of the VGCNF surfaces compared to the rest of the system after resin curing. Bulk nano-reinforced material properties are highly dependent on the interphase features because of the high surface area to volume ratio of nano-reinforcements. For example, higher length scale micromechanical calculations suggest that the volume fraction and properties of the interphase can have a profound effect on bulk material properties. Interphase formation, microstructure, geometries, and properties in VGCNF-reinforced polymeric composites have not been well characterized experimentally, largely due to the small size of typical nano-reinforcements and interphases. Therefore, MD simulations offer an alternative means to probe the nano-sized formation of the interphase and to determine its properties, without having to perform fine-scale experiments. A robust crosslinking algorithm for VE resin was then developed as a key element of this research. VE resins are crosslinked via free radical copolymerization account for regioselectivity and monomer reactivity ratios. After the VE crosslinked network was created, the constitutive properties of the resin were calculated. This algorithm will be used to crosslink equilibrated VE resin systems containing both pristine and oxidized VGCNFs. An understanding of formation and kinematics of a crosslinked network obtained via MD simulations can facilitate nanomaterials design and can reduce the amount of nanocomposite experiments required. VGCNF pull-out simulations will then be performed to determine the interfacial shear strength between VGCNFs and the matrix. Interphase formation, thickness and interfacial shear strength can directly feed into higher length scale micromechanical models within a global multiscale analysis framework.

URI

https://hdl.handle.net/11668/19787

Comments

polymer||composites||interphase formation||crosslinking||molecular dynamics||vinyl ester||carbon nanofiber

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