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Structure and Dynamics of Swollen Polymer Brushes

Sun, Liang
http://orcid.org/0000-0002-3263-3828
http://rave.ohiolink.edu/etdc/view?acc_num=akron1499675793233755

Abstract Details

2017, Doctor of Philosophy, University of Akron, Polymer Science.
A polymer brush is a monomolecular film in which each polymer chain is attached at one end to a surface or interface. Tremendous attention has been paid to both the basic science and technology of polymer brushes, due to their special properties, which stem from their unique structure arising from the tethering of polymer chains. Especially, research and many applications involve polymer brushes in the swollen state. The main objective of the research presented in this dissertation was to determine the structure and dynamics of polymer brushes under swollen conditions. The structure of polystyrene brushes swollen in toluene vapor has been determined using neutron reflectivity. For high grafting density brushes, the scaling of the thickness of the brush swollen in solvent vapor with chain length and grafting density agrees quantitatively with the scaling reported for densely grafted brushes swollen in liquid. Deep in the brush, next to the substrate, the shape of the segment concentration profile is the same whether the brush is swollen by liquid or by vapor. Differences in the segment concentration profile are manifested primarily in the swollen brush interface with the surrounding fluid. The interface of the polymer brush swollen in vapor is much more abrupt than that of the same brush swollen in liquid, which agrees well with a simple SCF calculation. This sharper interface should have important implications for fluctuations at the brush surface and the compressibility of the brush surface in the swollen state. The surface dynamics of polystyrene brushes swollen in toluene vapor have been investigated using X-ray photon correlation spectroscopy. No surface height fluctuations are observable in the currently available experimental time and length scale window for various strongly swollen brushes of grafting densities from 0.04 to 0.61 chains/nm2 and swollen thicknesses from 11 to 105 nm. This is remarkable, considering how highly plasticized the layers are from the standpoint of segmental dynamics. The surfaces of the vapor swollen brushes behave like solid surfaces on time scales and length scales pertinent to many practical applications. We attribute slowing of the surface fluctuations to the entropic penalty that has to be paid for fluctuations (which are a collective motion) to occur. Even the surface fluctuations of a 47 nm thick layer of liquid toluene atop a swollen brush are strongly altered by the presence of the adjacent brush chains. Polymer films containing a layer of untethered chains on top of a brush have been studied by probing the diffusion dynamics of embedded gold nanoparticles with X-ray photon correlation spectroscopy. We found that the local diffusion slows significantly with an increase in the concentration of segments from tethered chains. This change in mobility with depth is more complicated than that envisioned in simple models of a layer of untethered chains with bulk viscosity sitting on top of an immovable brush.
Mark Foster (Advisor)
Ali Dhinojwala (Committee Chair)
Mesfin Tsige (Committee Member)
Matthew Becker (Committee Member)
David Simmons (Committee Member)
Materials Science; Physics; Polymers
swollen polymer brush; surface fluctuations; dynamics;

Recommended Citations

Citations

  • Sun, L. (2017). Structure and Dynamics of Swollen Polymer Brushes [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499675793233755

    APA Style (7th edition)

  • Sun, Liang. Structure and Dynamics of Swollen Polymer Brushes. 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1499675793233755.

    MLA Style (8th edition)

  • Sun, Liang. "Structure and Dynamics of Swollen Polymer Brushes." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1499675793233755

    Chicago Manual of Style (17th edition)

akron1499675793233755
839
© 2017, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.