Abstract
Here, we systematically interrogate the effects of grafting single-walled (SWNT) and multi-walled carbon nanotubes (MWNT) to polymer matrices by using molecular dynamics (MD) simulations. We specifically investigate key material properties that include interfacial load transfer, alteration of nanotube properties, and dispersion of nanotubes in the polymer matrix. Simulations are conducted on a periodic unit cell model of the nanocomposite with a straight carbon nanotube and an amorphous polyethylene terephthalate (PET) matrix. For each type of nanotube, either 0%, 1.55%, or 3.1% of the carbon atoms in the outermost nanotubes are covalently grafted onto the carbon atoms of the PET matrix. Stress-strain curves and the elastic moduli of nanotubes and nanocomposites are determined based on the density of covalent grafting. Covalent grafting promotes two rivalling effects with respect to altering nanotube properties, and improvements in interfacial load transfer in the nanocomposites are clearly observed. The enhanced interface enables external loads applied to the nanocomposites to be efficiently transferred to the grafted nanotubes. Covalent functionalization of the nanotube surface with PET molecules can alter the solubility of nanotubes and improve dispersibility. Finally, we discuss the current limitations and challenges in using molecular modelling strategies to accurately predict properties on the nanotube and polymers systems studied here.
Highlights
At each step of twisting, number of grafting sites in outermost sidewall of the tube increases. This arises from the atoms 3in the other edge of nanotubes are quasi-statically displaced based on the defined sp hybridization of carbon atoms in carbon nanotubes (CNTs) that are bonded by ethyl functional groups
All of the elastic constants decrease as the number of grafting sites in outermost sidewall of the tube increases. This arises from the sp3 hybridization of carbon atoms in CNTs that are bonded by ethyl functional groups
The improved dispersibility of multi-walled carbon nanotubes (MWNT) by covalent grafting prompts a reconsideration ofHere the molecular unit cell model in Figure 2.toInevaluate the molecular model used in this study,of an molecular dynamics (MD) simulation was performed the effects of covalent grafting and other MD
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The issue of CNT waviness and defects arise from the intrinsic properties of CNTs, while CNT dispersion in the polymer matrix and corresponding interfacial load transfer rely on interactions among the embedded CNTs and host Solutions to the latter two factors are important to enable the practical applications and commercialization of CNT-based nanocomposites and are often approached chemically modifying the CNT surface [19]. It remains uncertain whether covalent grafting is an efficient method to improve the properties of CNTs-polymer nanocomposites This is because covalent grafting promotes two competing effects: (1) improvements to interfacial load and phonon transfer and (2) alteration of CNT properties. Even if the Hildebrand solubility parameter cannot be quantitatively correlated with physical properties of nanocomposites, it provides a useful measure of the extent of dispersion of CNTs in the polymer matrices.
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