Physical Aging of Confined Polymer Films by Use of a NewStreamlined Ellipsometry Procedure Público

Abstract

A new streamlined ellipsometry procedure for measuring the physical aging of confined polymer films is discussed. Supported polystyrene films both bulk (2.5 μm) and thin (down to 30 nm) on native silicon were used to test this ellipsometry procedure. Four different methods to calculate the physical aging rate, ß, of these confined polymer films are compared: one method involving Struik's original definition of physical aging rate, one method involving the height of the polymer film normalized at 10 minutes into the run h0 , one method involving the Lorentz-Lorenz equation, and a final method which uses the thermal expansion coefficient of a glassy polymer film and the change in the index of refraction over time. Using these four methods on the supported polystyrene films, the calculated physical aging rate produces curves of physical aging rate against aging temperature characteristic of those in the literature. The second method out of four is chosen, ß = -(1/h0) (dh/dlog t), as the best way to measure the physical aging rates of confined polymer films. Furthermore, the experimental time is optimized to 360 minutes of physical aging. The dependence of physical aging rate on film thickness is also tested. Below 100 nm in film thickness, a decrease in physical aging rate with decreasing film thickness is observed. This behavior may be explained by a gradient in the physical aging rate as a function of depth, as has been previously reported in the research literature. Now that it is known that the new ellipsometry procedure correctly characterizes the physical aging of supported polystyrene films, the physical aging behavior of different polymers in a supported state can be tested, as well as the physical aging of polystyrene in a free-standing state.

Table of Contents

Contents

1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

1.1 Glass Transition in Polymers . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Physical Aging in Bulk Polymers . . . . . . . . . . . . . . . . . . . . 3

1.3 Physical Aging in Thin Polymer Films . . . . . . . . . . . . . . . . . 7

1.3.1 Physical Aging in Thin Polymer Films, Stiff-Backbone . . . . 7

1.3.2 Physical Aging in Thin Polymer Films, Flexible C-C Backbone 11

1.3.3 Possible Source of the Differences in Physical Aging in Thin

Polymer Films . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

1.4 Scope of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2 Experimental Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.1 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 Rotating Compensator Ellipsometer . . . . . . . . . . . . . . . . . . . 15

2.2.1 Components of Ellipsometer . . . . . . . . . . . . . . . . . . . 17

2.2.2 Relevant Equations of Ellipsometry . . . . . . . . . . . . . . . 18

2.2.3 Modeling and Fitting Ellipsometry Data . . . . . . . . . . . . 26

2.3 Glass Transition Temperature Measurements . . . . . . . . . . . . . . 28

2.4 Experimental Procedure for Physical Aging Measurements . . . . . . 29

2.4.1 Comparison of Physical Aging Procedure to Existing Literature 31

3 Physical Aging Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33

3.1 Physical Aging Results . . . . . . . . . . . . . . . . . . . . . . . . . . 33

3.2 Determination of Physical Aging Rate ß . . . . . . . . . . . . . . . . 38

3.2.1 Method 1 Film Thickness Normalized at h∞ . . . . . . . . . . 40

3.2.2 Method 2 Film Thickness Normalized at h0 . . . . . . . . . . 43

3.2.3 Method 3 Lorentz-Lorenz Equation . . . . . . . . . . . . . . . 45

3.2.4 Method 4 Index of Refraction . . . . . . . . . . . . . . . . . . 50

3.3 Comparison of Temperature Dependence of Physical Aging Rate ß . . 53

3.4 Optimization of Physical Aging Time . . . . . . . . . . . . . . . . . . 55

3.5 Dependence of Physical Aging Rate on Film Thickness . . . . . . . . 56

4 Conclusions and Future Work . . . . . . . . . . . . . . . . . . . . . . 61

4.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

5 Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

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School	Laney Graduate School
Department	Physics
Degree	MA
Submission	Dissertation
Language	English
Research Field	Physics, Condensed Matter
Palavra-chave	ellipsometry confinement polystyrene physical aging polymer
Committee Chair / Thesis Advisor	Roth, Connie, Emory University
Committee Members	Weeks, Eric, Emory University Warncke, Kurt, Emory University Gallivan, Justin, Emory University

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