Obstacles and Solutions to Studying Functional Adhesives Using Vibrational Sum-Frequency ...

187 Pages·2016·3.69 MB·English

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Theses and Dissertations
2013-12-01
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Angela Renee Andersen
Brigham Young University - Provo
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Andersen, Angela Renee, "Obstacles and Solutions to Studying Functional Adhesives Using Vibrational
Sum-Frequency Generation Spectroscopy" (2013). Theses and Dissertations. 4267.
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Obstacles and Solutions to Studying Functional Adhesives Using Vibrational Sum-Frequency
Generation Spectroscopy

Angela Renée Andersen

A dissertation submitted to the faculty of
Brigham Young University
in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

James E. Patterson, Chair
Matthew C. Asplund
Steven R. Goates
Thomas A. Knotts
Eric T. Sevy

Department of Chemistry and Biochemistry
Brigham Young University
December 2013

Copyright ©2013 Angela Renée Andersen
All Rights Reserved
ABSTRACT

Obstacles and Solutions to Studying Functional Adhesives Using Vibrational Sum-Frequency
Generation Spectroscopy

Angela Renée Andersen
Department of Chemistry and Biochemistry, BYU
Doctor of Philosophy

Important aspects of adhesion occur at interfaces, including structures that may be
different from those in the bulk materials. However, probing the orientation of molecules in
functional adhesives poses a significant challenge because adhesive molecules are always
located at a buried interface. The limited penetration depth of surface-specific analysis prohibits
the study of buried interfaces using those techniques. The large quantity of bulk molecules
relative to the adhesive molecules interacting at the interface results in the bulk signal swamping
out adhesive signal in bulk analysis techniques. An interface-specific technique is required to
study functional adhesives. One such technique that has shown promise in recent years is
Vibrational sum frequency generation (VSFG) spectroscopy. This technique is useful for
studying interactions that occur at surfaces and interfaces because it selectively probes regions of
broken inversion symmetry.

Despite the ability of VSFG to isolate signal from a buried interface, a non-resonant
signal that is produced simultaneously with the resonant signal corrupts the vibrational data of
interest and greatly impedes reliable analysis of VSFG spectra. Over the last several years,
researchers have experimentally removed non-resonant signal by delaying the upconverting
pulse with respect to the initial excitation. Obtaining reliable results from VSFG data depends
upon complete removal of non-resonant signal. However, complete removal of non-resonant
signal presents a challenge because it can be present in spectra even when the indicators of non-
resonant signal are absent. By taking advantage of polarization selection rules for VSFG and the
differing symmetry of an azimuthally isotropic film and an azimuthally non-isotropic substrate,
spectra containing non-resonant signal can be easily identified.

These and other advances in VSFG methodology have enabled the study of surface and
interfacial systems of interest. In a study of the effects of plasma treatment on polystyrene thin
films, plasma exposure was found to affect not only the free surface but also portions of the sub-
surface polymer, challenging previous assumptions that plasma effects are constrained to the
free surfaces of materials. The next step is to use VSFG to study functional adhesives under
known amounts of applied stress. An apparatus is in place to simultaneously collect VSFG
spectra during mechanical testing of a functional adhesive, and in preliminary studies, an
increase in VSFG non-resonant signal has been observed when a pulling force is applied to the
adhesive bond.

Keywords: adhesion, plasma treatment, surface spectroscopy, sum-frequency generation
spectroscopy, nonlinear spectroscopy, polymers, strength testing, spin-coating, signal processing
ACKNOWLEDGEMENTS

The work included in this dissertation represents one of my proudest accomplishments,
and I wish to thank some of the many people and organizations that made this great
accomplishment possible. During my graduate studies I have received funding from the U.S.
Airforce, and was awarded the Nicholes Maw Fellowship and Roland K. Robins Research
Fellowship. I am also grateful for the generous financial support I received from the Hayswood
Foundation in the form of the Elsie Downing Scholarship that completely funded my
undergraduate education and gave me the financial freedom to pursue this graduate degree.
I am thankful to have had Dr. Patterson as my academic adviser during my graduate
program who has provided helpful guidance and needed encouragement throughout this process.
My committee has also helped to guide my research and has helped motivate me to work
diligently throughout this time. I also thank the kind and helpful staff of the BYU Department of
Chemistry and Biochemistry, especially Janet Fonoimoana.
Last but not least, I thank my family and friends for their continuing support; my parents,
who always encouraged me to value education and taught me a love of learning, and my
husband, Aaron Andersen, who has helped me to see my potential and supported me emotionally
in the final stages of completing my graduate work.
CONTENTS
Chapter 1: Introduction and Background ................................................................................... 1
1.1 The challenge of probing molecular structures in functional adhesives .......................... 1
1.2 Overview of Vibrationally Resonant Sum-Frequency Generation Spectroscopy ............ 2
1.2.1 Symmetry requirements ............................................................................................ 3
1.2.2 VSFG theory ............................................................................................................. 5
1.3 VSFG Collection Methods ............................................................................................... 7
1.4 VSFG nonresonant signal .............................................................................................. 13
1.4.1 Ignoring or treating nonresonant signal as negligible ............................................. 14
1.4.2 Treating nonresonant signal as a background ......................................................... 16
1.4.3 Time-domain heterodyne-detected VSFG .............................................................. 18
1.4.4 Nonresonant suppression by visible pulse delay and variable time delay VSFG ... 23
1.4.5 Summary of methods for coping with nonresonant signal ..................................... 35
1.5 Studying functional adhesives using VSFG ................................................................... 38
1.6 My role ........................................................................................................................... 42
1.7 Summary ........................................................................................................................ 43
1.8 References ...................................................................................................................... 44
Chapter 2: Materials and Methods ............................................................................................ 47
2.1 Preparation of substrates for coatings ............................................................................ 47
2.1.1 Cutting silicon wafers ............................................................................................. 47
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2.1.2 Removal of previous coatings ................................................................................. 47
2.1.3 Piranha cleaning ...................................................................................................... 48
2.1.4 Final rinsing and drying .......................................................................................... 49
2.1.5 Sample naming........................................................................................................ 49
2.2 Spin-coating thin polymer films ..................................................................................... 49
2.2.1 Making polymer solutions ...................................................................................... 52
2.2.2 Spin coating procedure ........................................................................................... 53
2.2.3 Creating layered samples ........................................................................................ 54
2.3 Determining film thickness using spectroscopic ellipsometry ....................................... 55
2.4 Plasma Treatment ........................................................................................................... 56
2.5 Annealing ....................................................................................................................... 57
2.6 Vibrational sum-frequency generation spectroscopy ..................................................... 58
2.6.1 Spectrometer description ........................................................................................ 58
2.6.2 Initial alignment of the VSFG system .................................................................... 61
2.6.3 Daily alignment of the VSFG system ..................................................................... 62
2.6.4 Polarization Experiments ........................................................................................ 62
2.7 References ...................................................................................................................... 63
Chapter 3: Ensuring adequate suppression of nonresonant signal in vibrational sum-frequency
generation spectroscopy ................................................................................................................ 64
3.1 Introduction .................................................................................................................... 64
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3.1.1 Theoretical Treatment and Modeling Approach ..................................................... 68
3.2 Methods .......................................................................................................................... 73
3.2.1 Building Theoretical Models .................................................................................. 73
3.2.2 Experimental ........................................................................................................... 78
3.3 Results and Discussion ................................................................................................... 80
3.3.1 Resonant Attenuation of Nonresonant Signal ......................................................... 80
3.3.2 Incomplete Suppression of Nonresonant Response ................................................ 82
3.3.3 Polarization Considerations .................................................................................... 89
3.3.4 General Considerations and Recommendations ..................................................... 98
3.4 Conclusions .................................................................................................................... 99
3.5 References .................................................................................................................... 101
Chapter 4: Plasma Treatment of Polystyrene Thin Films Affects More than the Surface ..... 104
4.1 Abstract ........................................................................................................................ 104
4.2 Introduction .................................................................................................................. 105
4.3 Experimental Methods ................................................................................................. 107
4.4 Results & Discussion ................................................................................................... 109
4.4.1 Effects of Plasma on Bulk Polystyrene ................................................................. 109
4.4.2 Determining Relative Orientations from VR-SFG Data ....................................... 111
4.4.3 Substrate Dependent Response to Plasma Treatment ........................................... 118
4.4.4 The Effects of Annealing on Plasma-Treated Polymer ........................................ 121
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4.5 Conclusions .................................................................................................................. 124
4.6 References .................................................................................................................... 126
Chapter 5: Coupling Adhesion Measurements with VSFG Spectroscopy ............................. 128
5.1 Introduction .................................................................................................................. 128
5.2 General Methods and Equipment ................................................................................. 130
5.3 Coupling strength tester with laser system ................................................................... 131
5.4 Challenges with creating samples ................................................................................ 136
5.5 Efforts with tensile tester programs ............................................................................. 139
5.6 Preliminary data combining strength testing and VSFG spectroscopy ........................ 145
5.7 Conclusions and Future work ....................................................................................... 149
5.8 References .................................................................................................................... 150
Chapter 6: . Final Remarks and Future Work ......................................................................... 152
6.1 Final Remarks .............................................................................................................. 152
6.2 Future work .................................................................................................................. 154
6.3 References .................................................................................................................... 155
Chapter 7: Appendix ............................................................................................................... 156
7.1 Spin-coating parameter tables ...................................................................................... 156
7.1.1 Thin Solvent Layer ............................................................................................... 156
7.1.2 Polystyrene in Toluene ......................................................................................... 156
7.1.3 Poly(methyl methacrylate) in Nitromethane ......................................................... 157
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7.2 Substrate abbreviations for systematic naming ............................................................ 157
7.3 MATLAB Code for Theoretical Modeling .................................................................. 158
7.3.1 Custom functions used in modeling ...................................................................... 158
7.3.2 Modeling attenuated nonresonant signal .............................................................. 159
7.3.3 Modeling a resonant signal with nonresonant interference .................................. 160
7.3.4 Prompted MATLAB program for modeling an apodized spectrum of polystyrene
with or with a custom S/N and custom ratio of nonresonant to resonant signal amplitude 162
7.4 General instructions for using Instron 3345 tensile tester ............................................ 164
7.4.1 Programming a prompted test method .................................................................. 164
7.5 Prompted test "Adhesion Testing Method Starter" for adhesion samples ................... 167
7.5.1 Soft Key Assignments: ......................................................................................... 167
7.5.2 General .................................................................................................................. 167
7.5.3 Specimen ............................................................................................................... 168
7.5.4 Control .................................................................................................................. 170
7.5.5 Calculations........................................................................................................... 172
7.5.6 Results 1 ................................................................................................................ 172
7.5.7 Graph 1.................................................................................................................. 172
7.5.8 Graph 2.................................................................................................................. 173
7.5.9 Raw Data ............................................................................................................... 174
7.5.10 Reports .................................................................................................................. 174
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7.5.11 Test Prompts ......................................................................................................... 175
7.5.12 Reports Tab ........................................................................................................... 176
7.6 Running an adhesion test with the "AdhesionTesting Method Starter" method (or future
methods based on it) on Instron 3345 ..................................................................................... 176

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