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Origins and Implications of Translational/Reorientational Decoupling in Bulk and Nanoconfined Glass-Forming Liquids

Diaz Vela, Daniel Mauricio
http://orcid.org/0000-0003-3879-5534
http://rave.ohiolink.edu/etdc/view?acc_num=akron1544098271236867

Abstract Details

2018, Doctor of Philosophy, University of Akron, Polymer Engineering.
One of the most important questions in the field of noncommitment has been the nature and origin of the alterations in dynamics encountered near free surfaces. 25 years of study have generated a big amount of data describing the phenomenology. Nevertheless, despite the time an effort of the scientific community, there is no even consensus onto a clear picture of the phenomenology. It has been argued that certain characteristics like manner of the measurements, long range effects, and experimental onset temperature are absent in simulation experiments. Therefore, in this study we use molecular dynamics simulations of model polymers in bulk and thin film settings to rationalize some of the discrepancies encountered in the field. The first part of the study is aimed to understand the phenomenology behind the dynamical alterations near free interfaces. We demonstrate that these effects emerge from a temperature-independent rescaling of the local activation barrier. This rescaling manifests as a fractional power law decoupling relationship of local dynamics relative to the bulk. Moreover, we show that a two-barrier model of the glass transition rationalizes many seemingly discordant findings in the field. The timescale of the onset condition is shown to depend on chemistry and relaxation function, largely because of shifts in the high temperature activation barrier, indicating seeming `contradictions’ between various thin film measurements and simulations emerge from differences in onset timescale. These findings also have profound implications for the nature of the glass transition itself: they indicate that dynamic arrest in fragile glass formers involves two distinct barriers and involves a length scale that at most grows weakly and saturates on cooling. The second part of this study focuses on the description of local segmental dynamics via measurement of several relaxation functions (associated with translation and reorientation). We measure the whole distribution curve of segmental relaxation times for polymer systems with two stiffnesses and in bulk and thin film settings. We found that, regardless the dynamical function used, the stretch exponentiality character found in glass formers is only partially due to the spatial averaging over dynamical heterogeneous domains but also due to local non-exponential dynamics.
David Simmons, Dr. (Advisor)
Kevin Cavicchi, Dr. (Advisor)
Thein Kyu, Dr. (Committee Member)
Andrey Dobrynin, Dr. (Committee Member)
Bi-min Zhang Newby, Dr. (Committee Member)
146 p.
Physics; Polymers
Nanoconfinement effects; glass transition; molecular dynamics simulation; interfacial dynamics

Recommended Citations

Citations

  • Diaz Vela, D. M. (2018). Origins and Implications of Translational/Reorientational Decoupling in Bulk and Nanoconfined Glass-Forming Liquids [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1544098271236867

    APA Style (7th edition)

  • Diaz Vela, Daniel. Origins and Implications of Translational/Reorientational Decoupling in Bulk and Nanoconfined Glass-Forming Liquids. 2018. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1544098271236867.

    MLA Style (8th edition)

  • Diaz Vela, Daniel. "Origins and Implications of Translational/Reorientational Decoupling in Bulk and Nanoconfined Glass-Forming Liquids." Doctoral dissertation, University of Akron, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1544098271236867

    Chicago Manual of Style (17th edition)

akron1544098271236867
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This open access ETD is published by University of Akron and OhioLINK.