Investigating Light-Induced Film Thickness Changes in Polymer Films Labeled with an Azo Dye Restricted; Files Only

Abstract

The purpose of this thesis was to characterize the photomechanical creep response of bulk

poly[(methyl methacrylate)-co-(Disperse Red 1 methacrylate)] (PMMA-DR1) polymer films. To

do this, a procedure for carrying out photoexpansion measurements was created and optimized.

Sample preparation protocols were optimized to combat dissolution issues, and a blend of solvents

was employed to thoroughly dissolve the polymer. Existing photoexpansion measurement procedures

consist of illuminating a DR1-labeled polymer sample with a 532 nm laser, which creates an

internal stress within the polymer film due to the photoisomerization of the DR1 dye. The resulting

strain is measured as an increase in film thickness using ellipsometry. These protocols were modified

to better suit PMMA-DR1 and to minimize error in the data. Additionally, a sample thermal

reset protocol was developed to allow for greater reproducibility and to ensure that multiple measurements

could be conducted on a single sample. Photoexpansion behavior was observed over a

range of different temperatures and laser powers, and it was found that the % expansion observed

upon illumination of the sample increased with increasing temperature and with increasing laser

power. During these measurements, a background decrease in film thickness was observed. Film

anisotropy was investigated as a possible cause of this decay, but it is unlikely that this is the case.

This background decay was observed to be affected by both changes in laser power and changes in

temperature. It is possible that this decay is caused by adding mechanical energy to the system due

to increased photoisomerization from increased laser power. The decay was also observed to be

larger at higher temperatures. The stress-strain response of PMMA-DR1 was modeled using the

Generalized Voigt-Kelvin model, which models the strain relaxation curve as a stretched exponential

decay. Further insight into the photomechanical stress-strain behavior of PMMA-DR1 could

yield a novel technique for the local, nanoscale measurement of polymer modulus.

Table of Contents

Chapter 1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Motivation: Property Changes in Polymer Thin Films . . . . . . . . . . . . . . . . 1

1.1.1 Glass Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.2 Glass Transition in Polymer Thin Films . . . . . . . . . . . . . . . . . . . 2

1.1.3 Stress and Strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.1.4 Modulus of Polymer Thin Films . . . . . . . . . . . . . . . . . . . . . . . 4

1.2 Photoisomerization of Disperse Red 1 . . . . . . . . . . . . . . . . . . . . . . . . 6

1.3 Existing Work Done with Disperse Red 1 . . . . . . . . . . . . . . . . . . . . . . 8

1.4 Goals of Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Chapter 2: Existing Experimental Methods . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.1 Ellipsometry Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.1.1 Polarization of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.1.2 Light and Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1.3 Fundamental Equation of Ellipsometry . . . . . . . . . . . . . . . . . . . . 16

2.2 Ellipsometry Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.2.1 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.2.2 Measurement of Intensity Ratios and Layer Model Analysis . . . . . . . . 18

Chapter 3: Developing Protocol for Photoexpansion Measurements . . . . . . . . . . . 20

3.1 Making High Quality PMMA-DR1 Films . . . . . . . . . . . . . . . . . . . . . . 20

3.2 Basic Protocol for Photoexpansion Measurements . . . . . . . . . . . . . . . . . . 20

3.2.1 Ellipsometer Setup and Data Collection Protocol . . . . . . . . . . . . . . 20

3.2.2 Laser Control Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2.3 Improvements and Adjustments to Protocol . . . . . . . . . . . . . . . . . 22

3.2.4 Sample Thermal Reset Protocol . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.5 Standard Isotropic Layer Model . . . . . . . . . . . . . . . . . . . . . . . 25

3.2.6 Impact of Varying Laser Power . . . . . . . . . . . . . . . . . . . . . . . . 26

3.3 Best Protocol for Photoexpansion Measurements . . . . . . . . . . . . . . . . . . 31

3.4 Testing of Anisotropic Layer Model . . . . . . . . . . . . . . . . . . . . . . . . . 32

Chapter 4: Temperature Dependence of Photoexpansion and Analysis . . . . . . . . . . 36

4.1 Measuring Photoexpansion at Different Temperatures . . . . . . . . . . . . . . . . 36

4.2 The Spring-Dashpot Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.2.1 Spring-Dashpot Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.2.2 The Voigt-Kelvin Element and Three Parameter Model . . . . . . . . . . . 40

4.2.3 Stretched Exponential and Generalized Voigt-Kelvin Model . . . . . . . . 44

4.3 Data Fitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Chapter 5: Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.1 Summary of Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

About this Honors Thesis

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• Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.

School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, General
Keyword	Polymer Physics Soft Matter Physics
Committee Chair / Thesis Advisor	Connie Roth, Emory University
Committee Members	Justin Burton, Emory University Simon Blakey, Emory University

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