self-healing mechanism and application of acrylic materials

186 Pages·2017·9.37 MB·English

by  Fan Fan

SELF-HEALING MECHANISM AND APPLICATION OF
ACRYLIC MATERIALS

A Thesis Submitted to the College of
Graduate Studies and Research
In Partial Fulfillment of the Requirements
For the Degree of Doctor of Philosophy
In the Department of Mechanical Engineering
University of Saskatchewan
Saskatoon

By
Fan Fan

© Copyright Fan Fan, December, 2016. All rights reserved.
PERMISSION TO USE
In presenting this thesis in partial fulfillment of the requirements for a postgraduate degree from
the University of Saskatchewan, I agree that the Libraries of this University may make it freely
available for inspection. I further agree that permission for copying of this thesis in any manner,
in whole or in part, for scholarly purposes may be granted by the professor who supervised my
thesis work or, in their absence, by the Head of the Department or the Dean of the College in which
my thesis work was done. It is understood that any copying or publication or use of this thesis or
parts thereof for financial gain shall not be allowed without my written permission. It is also
understood that due recognition shall be given to me and to the University of Saskatchewan in any
scholarly use which may be made of any material in my thesis.
Requests for permission to copy or to make other use of material in this thesis in whole or part
should be addressed to:

Head of the Department of Mechanical Engineering
57 Campus Dr.
University of Saskatchewan
Saskatoon, Saskatchewan (S7N 5A9)

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ABSTRACT
Self-healing materials have attracted significant attention from researchers during last decades.
However, self-healing materials cannot find practical applications yet due to a weak mechanical
strength. Recently, it was identified that an acrylic elastomer, VHB 4910, has an excellent self-
healing ability accompanied with a good mechanical strength. This material has been used to
fabricate artificial muscles because it has unique dielectric properties.
Our study demonstrated that VHB 4910 has a self-healing ability. The self-recovery and self-
healing ability of this material after separation by cutting was tested by unidirectional and cyclic
tensile tests. It was demonstrated that the strength can be completely recovered or even improved
when an elevated temperature is used to accelerate the healing process. The self-healing
mechanism was also analyzed by recording the Raman spectra at different distances from the cut
and at various times. Analysis of Raman spectra and X-ray diffraction experiments were used to
generate a support for the proposed model of self- healing. According to this model the self-
healing mechanism of the acrylic elastomer can be attributed to the synergistic effect of the re-
association of hydrogen bonding and the diffusion of molecular chains.
Furthermore, another application of self-healing materials was proposed in this research. The
coating that has not only the self-healing ability but also highly improved corrosion resistance was
developed. In this research, a self-healing anticorrosion coating via layer-by-layer (LbL) assembly
of the poly(acrylic acid) and poly(ethylene imine) was prepared on the magnesium alloys and
electrogalvanized steel (EGS). This coating exhibits a rapid self-healing ability in the presence of
water. The self-healing ability can be attributed to the swelling behavior of the damaged area of
the coating. In the healing process, water played a role of plasticizer and allowed to increase the
mobility of the molecular chains in the polyelectrolyte coating. When graphene oxide (GO) was
added into the multilayer coating the corrosion resistance improved by two orders compared to the
bare magnesium alloy. The GO layer acts as a strong barrier against the penetration of the corrosive
electrolytes and provides an extended corrosion protection to the substrate. Therefore, the
proposed multilayer coating with the addition of GO has a rapid self-healing ability and an
excellent corrosion resistance.

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ACKNOWLEDGEMENTS
First of all, I would like to appreciate China Scholarship Council (CSC) for their generous
sponsorship for my living expenses in Canada during last 4 years.
I would like to thank my committee members, Prof. Torvi, Prof. Szyszkowski, Prof. Boulfiza, Prof.
Meda and Prof. Guo. You showed your expertise during all my committee meeting by which I
received many useful comments on my project. These comments did help me improve my research.
I would like to express my many thanks to all the colleagues who helped me during last four years.
I still remember the first time when I got a chance to operate the SEM and XRD machine. It is
Siyamak and Hamed who instructed me with their most patience. I won’t forget the time with Lina,
Ming, Xu and Chunyu when we discussed our research and shared our ideas. It is the brainstorm
we experienced that stimulated and promoted my research.
I also appreciate our department assistant, Mr. Rob Peace, who provided a lot of help at the
beginning of my arrival. The whole laboratory including the rules and the facilities were new to
me. It is his extremely patience and kind assistance that helped me survive and progress.
Finally, I want to give my most respect and appreciation to my supervisor, Prof. Szpunar. I really
appreciate Prof. Szpunar who accepted my application and gave me the chance to study in such a
beautiful university. It is not easy to adapt to a new lifestyle which I have never experienced before,
not to mention the research transition from mechanical manufacture to materials science. It is the
trust from Prof. Szpunar that helped me successfully catch up the studying rhythm and narrow my
knowledge gap.

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DEDICATION
This thesis is dedicated to my wife and my parents without whom it cannot be completed.

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TABLE OF CONTENTS
PERMISSION TO USE ................................................................................................................. i
ABSTRACT ................................................................................................................................... ii
ACKNOWLEDGEMENTS ........................................................................................................ iii
DEDICATION.............................................................................................................................. iv
TABLE OF CONTENTS ............................................................................................................. v
LIST OF TABLES ........................................................................................................................ x
LIST OF FIGURES ..................................................................................................................... xi
ACRONYMS .............................................................................................................................. xvi
1. Introduction ............................................................................................................................... 1
1.1. Background of self-healing .................................................................................................. 1
1.2. Motivations .......................................................................................................................... 2
1.2.1. The self-healing acrylic elastomer VHB 4910 .............................................................. 2
1.2.2. The importance to protect magnesium alloys ............................................................... 3
1.2.3. Addition of graphene oxide .......................................................................................... 3
1.3. Objectives ............................................................................................................................ 4
2. Literature Review ..................................................................................................................... 7
2.1. Overview .............................................................................................................................. 7
2.2. The mechanism of self-healing materials ............................................................................ 8
2.2.1. Hydrogen bonding ........................................................................................................ 8
2.2.2. Hydrophobic interactions .............................................................................................. 9
2.2.3. Electrostatic attractions ............................................................................................... 11
2.2.4. Reversible covalent bonding ....................................................................................... 12
2.2.5. Encapsulated healing agent ......................................................................................... 13
2.3. The application of self-healing materials ........................................................................... 14
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2.3.1. Self-healing anticorrosion coating .............................................................................. 14
2.3.2. Self-healing superhydrophobic coating ...................................................................... 16
2.3.3. Self-healing barrier membranes .................................................................................. 17
2.4. Summary ............................................................................................................................ 18
3. Experimental Methodology .................................................................................................... 20
3.1. Overview ............................................................................................................................ 20
3.2. The deformation mechanism behind the tensile tests of acrylic elastomer ....................... 21
3.2.1. The entropic contribution to the elastomer deformation ............................................. 21
3.2.2. The energetic contribution to the elastomer deformation ........................................... 23
3.2.3. The experimental setup ............................................................................................... 23
3.3. The assembly mechanism of layer-by-layer (LbL) technique ........................................... 24
3.3.1. The growth mechanism of LbL assembly of polyelectrolytes .................................... 24
3.3.2. The thermodynamic aspect of LbL assembly of polyelectrolytes .............................. 26
3.3.3. The experimental setup ............................................................................................... 27
3.4. The analysis of corrosion mechanism by electrochemical impedance spectroscopy (EIS)28
3.4.1. The electrochemical aspect of corrosion ..................................................................... 28
3.4.2. The basics of EIS ........................................................................................................ 29
3.4.3. The experimental setup ............................................................................................... 33
3.5. The working mechanisms of other characterization techniques ........................................ 33
3.5.1. X-ray diffraction (XRD) ............................................................................................. 33
3.5.2. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS)
............................................................................................................................................... 34
3.5.3. Raman spectroscopy ................................................................................................... 34
3.6. Summary ............................................................................................................................ 36
4. The characterization and self-recovery behavior of acrylic elastomer VHB4910 ............ 38
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4.1. Overview ............................................................................................................................ 38
4.2. The characterization of the acrylic elastomer .................................................................... 39
4.2.1. The chemical structure of the acrylic elastomer ......................................................... 39
4.2.2. The tensile behavior of the acrylic elastomer ............................................................. 42
4.2.3. The deformation speed effect on the tensile tests ....................................................... 44
4.2.4. The hysteresis behavior of the acrylic elastomer ........................................................ 46
4.3. The self-recovery behavior of the acrylic elastomer .......................................................... 48
4.3.1. The strain dependence of self-recovery ability ........................................................... 48
4.3.2. The time dependence of self-recovery ability ............................................................. 50
4.4. Summary ............................................................................................................................ 52
5. The self-healing behavior and mechanism of acrylic elastomer VHB 4910 ...................... 54
5.1. Overview ............................................................................................................................ 54
5.2. Characterization of the self-healing behavior .................................................................... 55
5.2.1. The tensile test setup ................................................................................................... 55
5.2.2. The time-dependent self-healing ability ..................................................................... 55
5.3. Determination of the self-healing mechanism ................................................................... 59
5.3.1. The role of hydrogen bonding in self-healing............................................................. 60
5.3.2. The chain diffusion effect on self-healing .................................................................. 65
5.4. Summary ............................................................................................................................ 70
6. The poly(ethylene imine)/poly(acrylic acid) (PEI/PAA) multilayers self-healing coating on
magnesium alloy AZ31 ............................................................................................................... 72
6.1. Overview ............................................................................................................................ 72
6.2. Preparation and characterization of the PEI/PAA multilayers coating .............................. 73
6.2.1. Preparation of the cerium conversion layer ................................................................ 73
6.2.2. Preparation of the PEI/PAA multilayers ..................................................................... 74
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6.2.3. Characterization of the PEI/PAA multilayers ............................................................. 77
6.3. The corrosion resistance of the PEI/PAA multilayers coating .......................................... 77
6.3.1. The EIS results of the PEI/PAA multilayers............................................................... 77
6.3.2. The buffering effect of the PEI/PAA multilayers ....................................................... 80
6.4. The self-healing behavior and mechanism of the PEI/PAA multilayers ........................... 83
6.4.1. The self-healing behavior of the PEI/PAA multilayers .............................................. 83
6.4.2. The self-healing mechanism of the PEI/PAA multilayers .......................................... 85
6.5. Summary ............................................................................................................................ 88
7. The graphene oxide (GO) incorporated PEI/PAA multilayers self-healing coating on
magnesium alloy AZ31 ............................................................................................................... 90
7.1. Overview ............................................................................................................................ 90
7.2. Preparation and characterization of the multilayer coating ............................................... 91
7.2.1. Preparation of the multilayer coating .......................................................................... 91
7.2.2. Characterization of the multilayer coating .................................................................. 93
7.3. The self-healing behavior of the multilayer coating .......................................................... 97
7.4. The corrosion resistance of the multilayer coating ............................................................ 98
7.4.1. The EIS results of the multilayer coating ................................................................... 98
7.4.2. The polarization resistance and protection efficiency of the multilayer coating ...... 106
7.5. The degradation process and protection mechanism of the multilayer coating ............... 108
7.5.1. The degradation process of the multilayer coating ................................................... 108
7.5.2. The protection mechanism of the multilayer coating ............................................... 114
7.6. Summary .......................................................................................................................... 118
8. The application of PEI/PAA multilayers self-healing coating on electrogalvanized steel
..................................................................................................................................................... 119
8.1. Overview .......................................................................................................................... 119
8.2. Preparation and characterization of the PEI/PAA multilayers coating on EGS .............. 120
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8.3. The self-healing behavior of the PEI/PAA multilayers coating on EGS ......................... 123
8.4. The corrosion resistance of the PEI/PAA multilayers coating on EGS ........................... 124
8.5. The analysis of the corrosion products on bare EGS and (PEI/PAA)20 ......................... 133
8.6. The degrading process of bare EGS and (PEI/PAA)20 ................................................... 141
8.7. Summary .......................................................................................................................... 143
9. Conclusions and future work ............................................................................................... 144
9.1. Summary and Conclusions .............................................................................................. 144
9.2. Contributions to original knowledge ............................................................................... 146
9.3. Future works .................................................................................................................... 147
10. References ............................................................................................................................ 148
11. Appendix .............................................................................................................................. 169

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