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Effect of Copolymer Sequence on Mechanical Properties of Polymer Nanocomposites from Molecular Dynamics Simulations

Trazkovich, Alex
http://orcid.org/0000-0001-7575-8068
http://rave.ohiolink.edu/etdc/view?acc_num=osu1545930453011375

Abstract Details

2019, Doctor of Philosophy, Ohio State University, Chemical Engineering.
When incorporated into polymers, nanoparticles are known to modify the structure and dynamics of nearby polymer chains. Because nanoparticles have a high surface area to volume ratio, the properties of the polymer-nanoparticle interphase region can have a significant effect on the overall composite properties even at relatively low nanoparticle loading. In this work, we study the polymer-nanoparticle interphase region using molecular dynamics simulations, and we analyze the impact of a nanoparticle on local structure, dynamics, and viscoelastic properties. Of particular interest here is a class of systems which consists of nanoparticles incorporated into two-component copolymers where one component of the copolymer interacts more favorably with the nanoparticle than the other. In these systems, modifying the particular copolymer sequence may modify the interphase properties, and composite properties may therefore be adjusted even while maintaining the same overall monomer ratio. These systems have been the subject of several simulation studies focused on nanoparticle dispersion and assembly; however, relatively little simulation work has focused specifically on the impact of copolymer sequence on properties of the copolymer-nanoparticle interphase. We simulate a simple nanocomposite consisting of a single spherical nanoparticle surrounded by coarse-grained polymer chains. The polymers are composed of two different monomer types that differ only in their interaction strengths with the nanoparticle. By studying a series of regular multiblock copolymers with adjustable block length as well as a random copolymer, we examine the effect of copolymer sequence blockiness on the structure as well as the end-to-end vector autocorrelation, bond vector autocorrelation, and self-intermediate scattering function relaxation times as a function of distance from the nanoparticle surface. We find that, depending on block length, blocky copolymers can have faster or slower interphase dynamics than a random copolymer. Certain blocky copolymer sequences also lead to relaxation times near the nanoparticle surface that are slower than those of homopolymer systems composed of either component monomer. To analyze viscoelastic mechanical properties in the interphase, we measure local atomic stress fluctuations and use them to estimate the local stress autocorrelation as a function of distance from the nanoparticle. This local stress autocorrelation is then used to estimate the local dynamic modulus. This allows us to examine the effect of adjusting copolymer sequence on the dynamic modulus as a function of both frequency of excitation and distance from the nanoparticle. Notably, we find that certain copolymer sequences can lead to a higher viscoelastic hysteresis in the interphase than either homopolymer system, suggesting that tuning copolymer sequence could allow for significant control over nanocomposite dynamics. To demonstrate a possible application of adjusting material properties using copolymer sequence, we briefly consider a design challenge motivated by tire tread compounds, in which improving traction without sacrificing fuel economy requires increasing high-frequency hysteresis while maintaining low-frequency hysteresis. By considering an additional set of sequences motivated by our results from studying regular multiblock copolymers, we show how further adjusting copolymer sequence can be used to make progress toward this goal.
Lisa Hall (Advisor)
Isamu Kusaka (Committee Member)
Kurt Koelling (Committee Member)
Yiying Wu (Committee Member)
156 p.
Chemical Engineering
copolymer sequence; block copolymer; polymer nanocomposite; dynamic modulus; relaxation times; interphase properties; interphase dynamics; molecular dynamics; local dynamic modulus; tire mechanics

Recommended Citations

Citations

  • Trazkovich, A. (2019). Effect of Copolymer Sequence on Mechanical Properties of Polymer Nanocomposites from Molecular Dynamics Simulations [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1545930453011375

    APA Style (7th edition)

  • Trazkovich, Alex. Effect of Copolymer Sequence on Mechanical Properties of Polymer Nanocomposites from Molecular Dynamics Simulations. 2019. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1545930453011375.

    MLA Style (8th edition)

  • Trazkovich, Alex. "Effect of Copolymer Sequence on Mechanical Properties of Polymer Nanocomposites from Molecular Dynamics Simulations." Doctoral dissertation, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1545930453011375

    Chicago Manual of Style (17th edition)

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This open access ETD is published by The Ohio State University and OhioLINK.