Impact of Gradient in Dynamics at the Free Surface on the Physical Aging of Polystyrene Films and Its Connection to the Glass Transition Temperature Reductions

ORAL

Abstract

The glass transition and physical aging in nanoconfined polymer films have been heavily studied. Recently there have been an increasing number of studies pointing towards a gradient in mobility emanating from the free surface in these films. Using a new streamlined ellipsometry technique, we have measured the temperature dependence of the physical aging rate $\beta $ for both bulk (2430 nm) and thin (29 nm) polystyrene (PS) films supported on silicon. We find that the thinner films have reduced physical aging rates at all temperatures that are inconsistent with a simple shift in the temperature dependence of $\beta $ corresponding to the shift in $T_{g}$ observed in these films. The reduced $\beta $ values measured at all physical aging temperatures are consistent with a gradient in dynamics originating from the free surface of the film. Our data is well fit by a simple two-layer model that has been previously employed to explain the $T_{g}$ reductions in PS thin films, suggesting that the enhanced dynamics present at the free surface are responsible for both effects. The surface layer thickness of this two-layer model, which increases with decreasing temperature, characterizes the depth to which the enhanced mobility at the free surface propagates into the film.

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Authors

  • Justin Pye

    Dept of Physics, Emory University

  • Milind Purohit

    Univ of South Carolina, Benedict College, Sc 29204, Univ. South Carolina, Benedict College, Univ South Carolina, GA Tech, Central Microscopy Research Facility, University of Iowa, Iowa City, Iowa 52242, USA, Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka, Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA, Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, Department of Physics, University of Alabama at Birmingham, Birmingham, AL 35294, College of William \& Mary, Harvard University, Benedict College, SC 29204, Massachusetts Institute of Technology, University of Applied Science, Bielefeld, Germany, Francis Marion University, Physics Dept., Emory University, Emory University, Formerly Emory University, currently UCLA, Physics Department, Georgia State University, Univ. of Georgia, Dept. of Chemistry, Universidad Nacional de Quilmes, Argentina, Pr, Dr, Derpartment of Physics, Florida A\&M University, Tallahassee, FL-32307, Department of Physics, Emory University, Georgia Institute of Technology, Naval Research Laboratory, University of Alabama, Tsinghua University, Lawrence Berkeley National Laboratory, Vanderbilt University, Jagellonian Univ., Univ. of Bonn, North Carolina A\&T State Univ., North Carolina Central Univ., Duke Univ. and TUNL, Georgia State University, Dept of Physics, Emory University, Cell Biology Department, Emory University, Physics Department, Emory University, University of South Carolina

  • Milind Purohit

    Univ of South Carolina, Benedict College, Sc 29204, Univ. South Carolina, Benedict College, Univ South Carolina, GA Tech, Central Microscopy Research Facility, University of Iowa, Iowa City, Iowa 52242, USA, Department of Chemistry, University of Sri Jayewardenepura, Nugegoda, Sri Lanka, Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia 30303, USA, Department of Chemistry, University of Alabama at Birmingham, Birmingham, AL 35294, Department of Physics, University of Alabama at Birmingham, Birmingham, AL 35294, College of William \& Mary, Harvard University, Benedict College, SC 29204, Massachusetts Institute of Technology, University of Applied Science, Bielefeld, Germany, Francis Marion University, Physics Dept., Emory University, Emory University, Formerly Emory University, currently UCLA, Physics Department, Georgia State University, Univ. of Georgia, Dept. of Chemistry, Universidad Nacional de Quilmes, Argentina, Pr, Dr, Derpartment of Physics, Florida A\&M University, Tallahassee, FL-32307, Department of Physics, Emory University, Georgia Institute of Technology, Naval Research Laboratory, University of Alabama, Tsinghua University, Lawrence Berkeley National Laboratory, Vanderbilt University, Jagellonian Univ., Univ. of Bonn, North Carolina A\&T State Univ., North Carolina Central Univ., Duke Univ. and TUNL, Georgia State University, Dept of Physics, Emory University, Cell Biology Department, Emory University, Physics Department, Emory University, University of South Carolina

  • Connie Roth

    Dept of Physics, Emory University