Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


Sampath_Thesis.pdf (21.33 MB)

ETD Abstract Container

Abstract Header

Structure-Property Relationships in Model Ionomers from Molecular Dynamics Simulation

Sampath, Janani, Hall
http://rave.ohiolink.edu/etdc/view?acc_num=osu152543418206124

Abstract Details

2018, Doctor of Philosophy, Ohio State University, Chemical Engineering.
Ionomers are polymers that contain a small fraction of ionic groups covalently bound to a non-polar backbone. These bound ions along with free counterions tend to aggregate strongly in a low dielectric medium, giving rise to material properties different from the parent, uncharged polymer. Our research employs molecular dynamics (MD) simulations to understand the structure and dynamic behavior of these ionic aggregates under different conditions, to aid the development of improved materials such as ionomer composites for 3D printing. Prior work had established a useful CG model for acetic acid based ionomers, which we used in our work. First, we considered fully neutralized systems and applied uniaxial tensile deformation to understand the impact that aggregate morphology has on the mechanical properties of ionomers. The degree to which chains and ionic aggregates align was quantified; chains align significantly in response to deformation, while ionic aggregates are not as clearly aligned. The location of the ionomer peak (measure of interaggregate correlation) was tracked, and it was found that the length scale of aggregate order increases in the direction parallel to strain and decreases in the direction perpendicular to strain. The prior model for fully neutralized systems included COO– and Na+ but no COOH groups. To better model typical experimental systems that are only partially neutralized, we added additional `sticker' groups that represent COOH. These stickers are similar to uncharged monomer beads but with adjusted short ranged interaction strengths with each other and with ionic groups. Aggregate morphologies obtained using the sticker-based model are in good agreement with prior atomistic simulation results. Rheological properties were calculated, and were found to be in good agreement with experimental trends. A static electric field was applied to these partially neutralized ionomers. Aggregate morphology under the field was analyzed and compared with zero field morphology. Local and long-range order of the aggregates was also studied; the aggregate order increased in the presence of an electric field. Upon deforming the material after application of field, it was seen that the Young's modulus of the materials increased. To consider the impact of interfaces, a single spherical nanoparticle surrounded by partially neutralized ionomers was simulated. We considered two different sets of polymer bead-nanoparticle interaction parameters. It was found that aggregates are depleted near the nanoparticle surface relative to the bulk for the neutral nanoparticle-monomer interaction system. This trend reverses for the system with attractive nanoparticle-monomer interactions. There is an increase in the segmental dynamics near the surface relative to the bulk for the neutral nanoparticle, and a decrease in dynamics near the surface of the attractive nanoparticle. Relatedly, free standing thick ionomer films were simulated in order to examine the effect of interface on the adhesion of ionomers. Density profiles suggest that there is a pronounced structure of alternating neutral and charged groups close to the interface. Upon bringing two surfaces together, it was found that backbone mixing across the interface is higher for systems with lower ion density, while counterion mixing is greater for systems with higher ion density.
Lisa Hall (Advisor)
Stuart Cooper (Committee Member)
Vishnu Sundaresan (Committee Member)
205 p.
Chemical Engineering
Ionomers, Molecular Dynamics Simulations, Polymer Physics

Recommended Citations

Citations

  • Sampath, Hall, J. (2018). Structure-Property Relationships in Model Ionomers from Molecular Dynamics Simulation [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu152543418206124

    APA Style (7th edition)

  • Sampath, Hall, Janani. Structure-Property Relationships in Model Ionomers from Molecular Dynamics Simulation. 2018. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu152543418206124.

    MLA Style (8th edition)

  • Sampath, Hall, Janani. "Structure-Property Relationships in Model Ionomers from Molecular Dynamics Simulation." Doctoral dissertation, Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu152543418206124

    Chicago Manual of Style (17th edition)

osu152543418206124
208
© 2018, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.