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Molecular Dynamics Simulations of Adsorbed Polymer-Grafted Nanoparticles

Ethier, Jeffrey
http://orcid.org/0000-0001-7987-4058
http://rave.ohiolink.edu/etdc/view?acc_num=osu1555426585455568

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Ultrathin films containing neat polymer-grafted nanoparticles (PGNs) show promise for designing next-generation printed electronics and energy storage devices. Our research utilizes molecular dynamics (MD) simulations to understand the structure, entanglements, and mechanical properties of adsorbed neat PGN particles with varying graft density and polymer length, to provide insight towards the rational design of robust materials with precise spacing of inorganic particles. We first simulate individual and pairs of PGNs adsorbed to a surface with varying monomer-surface interactions. For individual PGNs, increasing the monomer-surface adsorption strength causes the polymer chains to spread out to increase contact with the surface, which agrees qualitatively with recent experimental findings. 2D density profiles and radial distribution functions are used to show the combined effect of polymer length and graft density on the monomer packing and canopy shape at various adsorption strengths. A more detailed entanglement analysis is then developed to analyze interparticle entanglements. Pairs of PGNs show increasing particle spacing and decreasing interparticle entanglements with increasing monomer-surface interaction strength. Monolayers of PGNs in a hexagonal spacing are simulated at a favorable surface interaction strength. High graft density particles remain well-structured in the monolayer; however, the moderately grafted particles are less organized due to increased exposure of the nanoparticle surface and is more apparent at weaker monomer-surface interaction strengths. The extent of interpenetration is quantified and shows that moderately grafted PGN particles are more interdigitated than their high graft density counterpart, which results in an increase in interparticle entanglements. Uniaxial deformation of the monolayer displays an increase in strain at failure, and therefore robustness, for moderately grafted particles due to increased interdigitation and interparticle entanglements. Next, the hexagonally spaced PGNs in the monolayer are cooled below the glass transition temperature and uniaxial stretching is applied. Craze growth and behavior in PGN monolayers is compared to pure thin films and experimental TEM images of qualitatively similar systems. Images of the crazes show the craze structure is qualitatively different than bulk crazes and are characteristic of thin films. PGN crazes appear more like a perforated sheet. Density profiles and stress-strain curves are analyzed to characterize the craze formation and deformation behavior. Our work provides a molecular scale picture of how moderately grafted particles exhibit better interdigitation, interparticle entanglements, and increased toughness in the melt or glassy state. Lastly, we introduce a new coarse-grained mapping method to closely match our graft densities to polystyrene-grafted surfaces. We compare brush heights between our simulations of polymer-grafted brush surfaces to experimental data and find good agreement. We then apply this mapping method to PGNs, and simulate PGNs adsorbed to polymer-grafted surfaces at various graft densities. The structure of the PGN and surface chains are quantified, and we relate chain conformations and PGN-brush interdigitation to the mobility of the particle on the surface. These results are a first step in understanding adsorption properties of PGNs on brush surfaces, specifically PGNs adsorbed to a gradient brush surface, which have applications for controlling the spacing and organization of PGNs in thin films.
Lisa Hall (Advisor)
Isamu Kusaka (Committee Member)
Kurt Koelling (Committee Member)
206 p.
Chemical Engineering
polymer-grafted nanoparticles; entanglements; molecular dynamics simulations; polymer physics

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Citations

  • Ethier, J. (2019). Molecular Dynamics Simulations of Adsorbed Polymer-Grafted Nanoparticles [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555426585455568

    APA Style (7th edition)

  • Ethier, Jeffrey. Molecular Dynamics Simulations of Adsorbed Polymer-Grafted Nanoparticles. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1555426585455568.

    MLA Style (8th edition)

  • Ethier, Jeffrey. "Molecular Dynamics Simulations of Adsorbed Polymer-Grafted Nanoparticles." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1555426585455568

    Chicago Manual of Style (17th edition)

osu1555426585455568
143
© 2019, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.