Nonthermal plasma surface modification of materials

Masaaki Okubo

Nonthermal
Plasma Surface
Modification
of Materials

Nonthermal Plasma Surface Modification
of Materials

Masaaki Okubo

Nonthermal Plasma Surface
Modification of Materials

Masaaki Okubo
Department of Mechanical Engineering
Graduate School of Engineering
Osaka Metropolitan University
Sakai, Japan

ISBN 978-981-99-4505-4 ISBN 978-981-99-4506-1 (eBook)

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Preface

This book describes various types of nonthermal plasma surface modification tech-
nologies for materials at varying atmospheric-pressure and low-temperature condi-
tions, and it is among the first to address these topics. Furthermore, this book aims to
bridge the gap between fundamental and technical aspects with respect to industrial
applications in material and plasma engineering. The main objective of this book is
to provide readers with an easy-to-understand resource that outlines the foundations
and application potential of nonthermal plasma surface modifications.

In recent years, the surface modification of materials has gained considerable
attention in the field of advanced manufacturing. The technology for the surface
modification of materials can be classified into two groups: (1) reduced-pressure
plasma treatment and (2) atmospheric-pressure plasma treatment. The latter has

many advantages, such as compatibility with industry apparatus, because a reduced-
pressure environment can be avoided. Compared to other treatments, nonthermal
plasma treatment offers the possibility of a strong and effective modification.

Typically, surface treatment using fluoroplastics, such as perfluoroalkoxy alkane
(PFA), polytetrafluoroethylene (PTFE; Teflon), and polychlorotrifluoroethylene
(PCTFE), is considered an original, unique, and successful feature. Fluoroplastics
have excellent characteristics such as chemical resistance, electrical insulation, heat
resistance, flame resistance, and high gas barrier properties, and therefore, they are
widely used. However, owing to their high hydrophobicity, they cannot be easily
bonded to other materials without losing these characteristics. My group has solved
this problem using our innovative atmospheric-pressure plasma hybrid processing
technology and achieved high adhesiveness for the first time. Our technology is
expected to be widely applied in the future.

Nonthermal plasma surface modification is an interdisciplinary field that is physic-
ochemical in nature and has applications in mechanical, electrical, and chemical
engineering. Given that practitioners in these fields hail from diverse backgrounds,
I strove to devise a technology that is sufficiently self-contained to be accessible to
engineers, scientists, and students from many fields.

v

vi Preface

The contents of the book are summarized as follows:
Chapter 1 defines plasma and outlines the fundamentals of nonthermal plasma
technologies. A method to generate atmospheric-pressure nonthermal plasma is
described. Chapter 2 addresses the fundamentals of surface treatment technolo-
gies and characterization. The principle of plasma graft polymerization, evaluation

method of surface treatment effects, and apparatus used for surface modification
characterization are described. Chapter 3 describes the hydrophilic treatment of
polymer surfaces and its applications. The principle and methods of plasma treat-
ment and plasma graft polymerization treatment are described. Furthermore, the
application of PTFE/plastic to millimeter-wave devices, development of organic
light emitting diode (OLED) elements, and improved adhesion of fluoropolymer
film to butyl rubber for biomedical applications are expounded. Chapter 4 describes
the hydrophilic treatment technology for textiles, filters, and glass and its appli-
cations. The surface treatment of fibers, apparel, and deodorization technology
using these treated materials are described. Chapter 5 covers the hydrophobic treat-
ment of polymer surfaces. Diamond-like carbon (DLC) plasma surface treatment
hydrophobic technology, catalyst surface treatment, and trends in other surface treat-
ments with plasma are explained. Chapter 6 describes the hydrophobic treatment
of plastic, glass, and metal surfaces and its applications. The principles of plasma
cleaning and surface activation are explained. Several examples of the implementa-
tion of hydrophobicity by plasma cleaning and activation are described, and plasma
corrosion-resistant chemical hybrid treatments are explained. Chapter 7 describes
plasma and electron-beam technologies used for surface treatment applications. The
principles of electron-beam technology for surface treatment and plasma jet steril-
ization of surfaces are described, and respective examples are provided. Chapter 8
describes measurement technology for functional groups generated by plasma treat-
ment. The characterization and analysis of functional groups can be used to eval-
uate the effect of surface modification. Suitable technologies for the analysis of
functional groups and chemical species formed by plasma treatment are described.
Concluding remarks summarize the contents of this book and outline future prospects.
The topics treated in this book are presented as self-contained descriptions derived
from literature, and Appendix presents supporting information on Sakai city where
this book was written, along with the principles of measurement apparatus for surface
treatment.
I hope technologists in industries, academic university professors, and graduate

students in engineering alike find this book useful. The unique elements of this book
can be expressed as follows:

1. Covers: Principle, apparatus, methods, and industry application examples of
nonthermal plasma surface modification technologies.

2. Explains: Principle and methods of nonthermal plasma surface modification
technologies, in particular, knowledge on the generation of atmospheric-pressure
plasma is provided.

Preface vii

3. Demonstrates: Successful industry application technologies for atmospheric-
pressure plasma surface treatment.

4. Introduces: Principle and methods of nonthermal plasma surface modification
technologies for beginner engineers and graduate students.

5. Readers: I strongly recommend this book for all those who work or intend to
work on the adhesion of poorly adhesive materials.

Our research group has a history of more than 20 years of performing research
projects on the surface modification for many companies toward the development
of new machines. These projects have provided us with a wide range of exciting
experiences. We aim to share our fascination with this technology through this book to
enable scientists and engineers to engage in it successfully. I believe that our research
work should be documented and it is vital that these technologies are conveyed to
the future generations. Most of these projects were conducted at Osaka Prefecture
University (currently Osaka Metropolitan University) in Sakai city, Osaka Prefecture,
Japan. Sakai city has prospered in ocean trade for centuries. In the sixteenth century,

it was called “Oriental Venice” or “Saccai” to Europeans, and it has been a prosperous
international trade port and home to many industries.

At present, Sakai city is an important industrial city in Japan with a large factory
zone in the coastal area. Sakai has a long tradition of metal manufacturing. I am
delighted to publish this book on the plasma surface treatment technology from
Osaka Metropolitan University, which is located in this traditional Japanese city.
This book covers recent developments in nonthermal technologies and their funda-
mental aspects. I have also described selected applications of surface modification
technologies. While some of these technologies have reached the commercial stage,
others are still in early development. This book provides technical details and test
results rooted in fundamentals of plasma engineering.

The author first wrote each chapter separately based on materials that have been
published previously as scientific papers, reviews, and book chapters, and then,
the contents were knit together to maintain comprehensive unity. I am grateful to
many individuals who assisted during the preparation of this book. I thank Ms.
Ayako Yoden for her meticulous typing of the handwritten manuscripts. It has
also been a pleasure to work with the editor of this book Mr. Smith Ahram Chae
and Mr. Rajesh Manohar, Project Coordinator—Total Service. Collaborations with
many colleagues over a number of years have been very enriching and enjoyable.
I have discussed the future prospects of various plasma treatment systems with
Dr. Tomoyuki Kuroki and Dr. Haruhiko Yamasaki of Osaka Metropolitan University,
Dr. Toshiaki Yamamoto and Dr. Hidekatsu Fujishima of Osaka Prefecture Univer-
sity, Dr. Keiichiro Yoshida of Osaka Institute of Technology, Dr. Takuya Kuwahara
of Nippon Institute of Technology, and Dr. Hashira Yamamoto of Nihon Yamamura
Glass Co., Ltd. Research studies performed with many students for over 20 years at
Osaka Prefecture University and Osaka Metropolitan University have been enriching
and enjoyable, and most of these are credited in this book through citations of their

viii Preface

published work. I have truly enjoyed studying and performing experiments on plasma
treatments. I hope that this book proves beneficial not only to material engineers and
students but also to professionals in other fields such as electrical, mechanical, chem-
ical, and environmental engineering who wish to gain essential knowledge on the
emerging plasma surface modification technologies.

Sakai, Japan Masaaki Okubo

Contents

1 Fundamentals of Nonthermal Plasma Technologies . . . . . . . . . . . . . . . . 1
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Generation of Atmospheric-Pressure Nonthermal Plasmas . . . . . . . 1
1.3 What Are Plasmas? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.4 Types of Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.5 Pulse Corona Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.6 Dielectric Barrier Discharge-Induced Plasmas . . . . . . . . . . . . . . . . . 6
1.7 High-Frequency Plasmas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7.1 Surface Discharge Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.7.2 Radio-Frequency Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.7.3 Microwave-Generated Plasma . . . . . . . . . . . . . . . . . . . . . . . . 12
1.8 Plasma Jet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.9 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2 Fundamentals of Surface Treatment Technologies
and Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.2 Mechanism of Surface Modification . . . . . . . . . . . . . . . . . . . . . . . . . . 17
2.3 Plasma Graft Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.4 Apparatus for Surface Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.5 Surface Characterization Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5.1 Contact Angle Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5.2 Evaluating Adhesive Properties by Peeling Test . . . . . . . . . 24
2.5.3 Result of Surface Analysis by ESCA (XPS) . . . . . . . . . . . . . 26
2.5.4 Result of FTIR Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.5.5 Result of SEM Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

ix

x Contents

3 Hydrophilic Treatment for Polymer Surfaces and Its
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.2 Plasma Treatment and Plasma Graft Polymerization
Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.1 Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.2.2 Examples of Plasma Treatment Electrodes . . . . . . . . . . . . . . 37
3.2.3 Principle and Example of Hydrophilic Plasma
Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.4 Plasma Surface Treatment and Plasma Graft
Polymerization Surface Treatment Mechanism . . . . . . . . . . 41
3.2.5 Structure of the Three Electrodes with Different
Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.2.6 Principle of Atmospheric-Pressure Plasma Graft

Polymerization and Adhesion Improvement
Mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.3 Atmospheric-Pressure Plasma Graft Polymerization
Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.1 Atmospheric-Pressure Plasma Graft Polymerization
Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.3.2 Surface Treatment Evaluation for PTFE Metal Plating . . . . 47
3.3.3 XPS Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
3.4 Applicability of PTFE/Plastics in Millimeter-Wave Devices . . . . . 56
3.4.1 Plastic Properties: Dielectric Constant, Dielectric
Loss Tangent, and Hydrophobicity . . . . . . . . . . . . . . . . . . . . 58
3.4.2 Small High-Performance Millimeter-Wave Band
Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
3.4.3 Applicability to High-Frequency Coaxial Cables . . . . . . . . 60
3.4.4 Method of Copper Plating on PTFE and Results . . . . . . . . . 61
3.4.5 Surface Treatment of Dielectric Cable . . . . . . . . . . . . . . . . . 64
3.4.6 Method of Nickel Plating on PTFE and Results . . . . . . . . . . 65
3.4.7 Microfabrication of Nickel Plating on PTFE . . . . . . . . . . . . 67
3.4.8 Applicability to Radome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
3.4.9 Plasma Hybrid Surface Treatment of
Fiber-Reinforced Composite Materials . . . . . . . . . . . . . . . . . 71
3.5 Development of OLEDs on PCTFE . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.5.1 Flexible OLED Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.5.2 Peeling Strength for PCTFE . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.5.3 XPS Analysis Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
3.5.4 SEM Observation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
3.5.5 Prototype Fabrication Procedure for OLED Device
on PCTFE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
3.6 Improved Adhesion of Fluoroplastic Film to Butyl Rubber . . . . . . 80
3.6.1 Application Example: Prefilled Syringe . . . . . . . . . . . . . . . . 80

3.6.2 Butyl Rubber and PTFE Film Composite Material . . . . . . . 82

Contents xi

3.6.3 Peeling Test of Fluoroplastic Film–Butyl Rubber
Composite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

3.6.4 Peeling Strength of the Composite Material . . . . . . . . . . . . . 88
3.6.5 Molecular-Level Adhesion Mechanism Between

Rubber and PTFE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
3.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

4 Hydrophilic Treatment Technology for Textiles, Filters,
and Glass and Its Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.2 Surface Treatment of Textiles and Apparels . . . . . . . . . . . . . . . . . . . 97
4.2.1 Principle of Functional Surface Treatment . . . . . . . . . . . . . . 97
4.2.2 Experimental Apparatus and Methods . . . . . . . . . . . . . . . . . . 99
4.2.3 Experimental Results and Discussion . . . . . . . . . . . . . . . . . . 104
4.3 Deodorization Technology Using Low-Temperature
Nonthermal Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
4.3.1 Plasma Deodorization Technology . . . . . . . . . . . . . . . . . . . . . 110
4.3.2 Methods for Producing and Measuring Performance
of Functional Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
4.3.3 Experimental Results and Explanation . . . . . . . . . . . . . . . . . 116
4.4 Increased Glass Surface Hydrophilicity by Nonthermal
Plasma Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
4.4.1 Definition of Contact Angle . . . . . . . . . . . . . . . . . . . . . . . . . . 118

4.4.2 Glass Surface Treatment
Using Atmospheric-Pressure NTP Irradiation . . . . . . . . . . . 119
4.4.3 Glass Surface Hydrophilicity Dynamically
Controlled by Nonthermal Plasma Actuator . . . . . . . . . . . . . 123
4.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

5 Hydrophobic Treatment for Polymer Surfaces . . . . . . . . . . . . . . . . . . . . 129
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
5.2 Preparing a Hydrophobic Material Surface by Fluorocarbon
Plasma Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
5.3 Radio-Frequency Plasma Reactors with Chemical Vapor
Deposition Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
5.4 Nonthermal Plasma Technology for Surface Modification . . . . . . . 133
5.5 Reaction Between Plasma and Polymer . . . . . . . . . . . . . . . . . . . . . . . 135
5.6 Surface Hydrophobicity by Laser Microfabrication . . . . . . . . . . . . . 138
5.7 Diamond-Like Carbon-Based Plasma Surface Treatment . . . . . . . . 138
5.8 Plasma-Treated Catalyst Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
5.9 Trends in Other Plasma-Based Surface Treatments . . . . . . . . . . . . . 140
5.10 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

xii Contents

6 Hydrophobic Treatments for Plastic, Glass, and Metal Surfaces
and Their Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
6.2 Definition of Plasma and Its Characteristics . . . . . . . . . . . . . . . . . . . 144
6.2.1 Definition of Plasma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
6.2.2 Plasma Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144

6.2.3 Thermal Equilibrium and Nonequilibrium Plasma . . . . . . . 145
6.2.4 Method to Evaluate Ionization Degree in Plasma . . . . . . . . 146
6.3 Principles of Plasma Cleaning and Surface Activation
Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.3.1 Overview of Plasma Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.3.2 Example of Electrode Systems for Reduced-Pressure
Plasma Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
6.3.3 Cleaning Using Atmospheric-Pressure Plasmas . . . . . . . . . . 151
6.3.4 Effects of Atmospheric-Pressure Plasma Cleaning . . . . . . . 152
6.3.5 Remote Plasma Cleaning and Cleaning by Ozone . . . . . . . . 154
6.4 Example of Plasma Cleaning and Enhanced Activation
of Hydrophilicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
6.4.1 Hybrid Plasma-Hydrophobic–Chemical Process . . . . . . . . . 155
6.4.2 Experimental Apparatus and Method . . . . . . . . . . . . . . . . . . 155
6.4.3 Test Results Obtained for Cleaning
and Hydrophilicity and Discussion . . . . . . . . . . . . . . . . . . . . 156
6.4.4 Hydrophobic Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
6.5 Hybrid Plasma–Anti-corrosion Process Treatment
(Aluminum Plate Surface Treatment) . . . . . . . . . . . . . . . . . . . . . . . . . 160
6.5.1 Ordinary and Hybrid Plasma Treatments . . . . . . . . . . . . . . . 160
6.5.2 Plasma Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
6.5.3 Treatment After Plasma Irradiation and Increased
Anti-corrosion Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
6.5.4 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
6.5.5 Corrosion Test Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
6.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

7 Plasma and Electron-Beam Technologies Used for Surface
Treatment Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
7.2 Plasma Hybrid Hydrophilic Treatment Process . . . . . . . . . . . . . . . . 171
7.2.1 Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
7.2.2 Examples of the Adhesion of Glass and PTFE . . . . . . . . . . . 172
7.3 Anti-fog Using Electron-Beam Irradiation Treatment Process . . . . 178
7.3.1 Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
7.3.2 Anti-fog Treatment Application Example . . . . . . . . . . . . . . . 180
7.4 Plasma Treatment for Medical Applications . . . . . . . . . . . . . . . . . . . 181
7.4.1 Surface Treatment for an Endoscope . . . . . . . . . . . . . . . . . . . 181
7.4.2 Plasma Jet Sterilization of Surfaces . . . . . . . . . . . . . . . . . . . . 181

Contents xiii

7.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184

8 Measurement Technology for Functional Groups Generated
by Plasma Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
8.2 Analysis of Functional Groups Generated by Plasma
Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
8.2.1 Functional Group Analysis of Plasma
Graft-Polymerized Acrylic Acid Film on PTFE
by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
8.2.2 Functional Group Analysis of Plasma
Graft-Polymerized Acrylic Acid Film on PTFE
by XPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
8.3 Analysis of Chemical Species Formed by Plasma Treatment . . . . . 191
8.3.1 Analysis of Byproducts During Treatment
of Ammonia Gas and Acetaldehyde Gas with Plasma

by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
8.3.2 Analysis of Byproducts During Treatment of CF4
Gas with ICP by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
8.3.3 Analysis of Byproducts During Treatment of Xylene
Gas with Plasma by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
8.3.4 Analysis of Byproducts During Plasma Treatment
of TEOS by FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
8.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

About the Author

Dr. Masaaki Okubo received his B.Eng., M.Eng., and Ph.D. degrees in mechanical
engineering from the Tokyo Institute of Technology, Tokyo, Japan, in 1985, 1987,
and 1990, respectively. He is Full Professor at the Department of Mechanical Engi-
neering, Osaka Metropolitan University, Sakai, Japan. In April 2022, Osaka Prefec-
ture University and Osaka City University were merged to form Osaka Metropolitan
University. His previous positions include Associate Professor at Osaka Prefec-
ture University, Assistant Professor at Tokyo Institute of Technology, and Assis-
tant Professor at Tohoku University. He also served as Invited Professor at Tohoku
University in 2015.

His current research interests include environmental applications of nonthermal
plasmas, particularly, nanoparticle control, electrostatic precipitators, aftertreatment
of clean diesel engines and combustors, and surface treatment of materials and their
biomedical applications. His works span multidisciplinary areas including electrical,

chemical, and mechanical engineering. Dr. Okubo has published more than 230
peer-reviewed and invited papers in scientific journals and has authored 33 books.

Dr. Okubo is Fellow of the Institute of Electrical and Electronics Engineers (IEEE)
and the Japan Society of Mechanical Engineers (JSME). He was Chairman of the
Environmental Engineering Division of the JSME in 2007. He served as Chairman
of the Electrostatic Process Committee of the IEEE Industry Application Society
during 2016–2018. He is Associate Editor of the IEEE Transactions on Industry
Applications, Kansai Branch Chair of the Institute of Electrostatics Japan, and Edito-
rial Board Member of the Journal of Electrostatics. He received the Environmental
Engineering Achievement Award of the Environmental Engineering Division of the
Japan Society of Mechanical Engineers in 2013.

xv

Chapter 1

Fundamentals of Nonthermal Plasma
Technologies

1.1 Introduction

In this chapter, the fundamentals of nonthermal plasma technologies are outlined.
The definition of plasma, as well as various types of plasmas and plasma gener-
ation methods, is described. Further, a method to generate atmospheric-pressure
nonthermal plasma is detailed.

1.2 Generation of Atmospheric-Pressure Nonthermal
Plasmas

Plasma is an ionic state of gas, and it can be generated using various methods. For
example, when easily ionized metals such as Cs and K are introduced into a high-
temperature gas stream of > 1000 °C, plasma is generated at atmospheric pressure.
The plasma can be generated at reduced pressure because ionization occurs easily.
Plasma treatment is performed to irradiate plasma to materials.

In industrial applications, plasma is generated using a metal electrode that is
energized by electric power as the insulation of gas is broken by the gradient of
the electric field. Various types of plasma generation methods, especially those of
atmospheric-pressure nonthermal (cold) plasma, are described in the following parts.
The plasma is explained in detail in the next section.

1.3 What Are Plasmas?

Figure 1.1 defines a plasma and details its generation process. The plasma is the fourth
state of matter after solid, liquid, and gas. Upon applying energy, such as electrical
energy, phase changes to solid, liquid, and gas occur. At atmospheric pressure, when

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2023 1

M. Okubo, Nonthermal Plasma Surface Modification of Materials,

/>
2 1 Fundamentals of Nonthermal Plasma Technologies

Energy Energy

Solid Gas Energy

Liquid

Dissociation of a molecule
Dissociation of an atom

C* B+ A− B+ Heavy particle
A- Negative ion
e− Plasma B+ B+ Positive ion
C* Atom (Radicals)
A− B+ e− C* e− Electron

Ionized gas

Fig. 1.1 Definition and generation process of plasmas. Plasma is induced when electrical or heat
energy is input to materials

electrical energy is introduced, the plasma is induced. Through the application of

plasma to a gas state, molecular and atomic dissociation occurs, and the plasma is
generated as a partially ionized gas. The plasma is composed of negative ions (A−),
positive ions (B+), atoms, radicals (C*), and electrons. Powerful activity may exist in

the plasma, and by the application of plasma to materials, their surfaces are activated

to usually show hydrophilic properties.

1.4 Types of Plasmas

The most typical plasmas are classified in Table 1.1. Familiar plasmas are known as
flames, aurora, lightning, fluorescent lights, etc. Four types of plasma are explained
here. A high-temperature plasma is in a high-temperature state of ≥ 10,000 °C, and

the electron temperature is equal to that of heavy particle temperature; examples
are atmospheric-pressure arc discharge and nuclear fusion plasmas. A low-pressure
plasma is generated by discharging under a pressure of several Pascals to several
hundred Pascals; examples are plasma–chemical vapor deposition (CVD) and surface
treatment. A nonequilibrium plasma is a state where the electron temperature is
much higher than that of heavy particle temperature. The atmospheric-pressure low-
temperature or cold plasma is generated by accelerating only electrons with a small
mass and high mobility under atmospheric pressure with a strong electric field, and it

1.4 Types of Plasmas 3

can be used for various purposes such as energy and environmental cleaning, surface
treatment, medical treatment, and biological application.

Various types of plasma generation are introduced. Figure 1.2 shows a lighting
ball or plasma globe, which is used as a room interior feature for lightning or as
a toy. A mixed rare gas such as neon at a low concentration is input into the glass
sphere shell, and a high-voltage electrode exists at the center of the glass sphere. A
high voltage is applied to the electrode, and a plasma filament is formed between the
central electrode and the spherical glass shell, and a bright beam of light appears to
be constantly extending.

Figure 1.3 shows a pulse corona-induced plasma reactor of approximately 2 m
in length. This type of plasma reactor consists of a coil-type outer ground electrode
and a centered wire electrode. Five pairs are observed in the figure, and the exhaust

Table 1.1 Classification and types of plasmas

Familiar plasmas Flames, aurora, lightning, fluorescent lights, etc.

Plasma types Characteristics
High-temperature plasma
A plasma in a high-temperature state of ≥ 10,000 °C or
higher, and electron temperature = heavy particle
temperature. Examples: atmospheric-pressure arc discharge
and nuclear fusion plasmas

Low-pressure plasma Plasma generated by discharging under a pressure of several
Pa to several hundred Pa. Examples: plasma–chemical vapor
deposition (CVD) and surface treatment

Nonequilibrium plasma Electron temperature >> heavy particle temperature

Atmospheric-pressure Plasma generated by accelerating only electrons with small
low-temperature or cold plasma mass and high mobility under atmospheric pressure with a
strong electric field. It can be used for various purposes.
Examples: energy and environmental cleaning, surface
treatment, medical treatment, and biological application

Fig. 1.2 Lighting ball or
plasma globe

4 1 Fundamentals of Nonthermal Plasma Technologies

Fig. 1.3 Pulse
corona-induced plasma
reactor (length = 2 m) [2]

gas passes perpendicular to the coil electrodes. This type of reactor was used in
an experiment on the decomposition of dioxins emitted from a garbage incinerator

[1, 2]. The structure of the coil-type outer ground electrode and the centered wire
electrode reactor is schematically shown in Fig. 1.4.

Figure 1.5 shows another example of an atmospheric-pressure plasma photograph
called the surface discharge, which is used for research on energy and environmental
applications. The inner surface of a cylindrical reactor is covered by an electrode, and
the inside of the wall of the cylinder is shown. A surface discharge-induced plasma
is generated inside the cylinder near the surface electrode. This type of surface
discharge-induced plasma apparatus is used for ozone generation aimed at NOx
and SOx reduction using the plasma–chemical hybrid process [2]. In the following
section, another type of surface discharge is explained.

1.5 Pulse Corona Plasmas 5

Fig. 1.4 Schematic diagram of a coil-type plasma reactor [2]

Fig. 1.5 Surface discharge
inside the cylinder reactor

1.5 Pulse Corona Plasmas

The methods that are used to generate atmospheric-pressure low-temperature plasmas
are explained. An atmospheric-pressure low-temperature plasma is generated by
applying a high voltage to a pair of electrodes. The pulse corona and surface discharge
methods are emerging as the most useful.

The pulse corona method involves electrical discharge using a pulse power supply
(~ 150 kV), and the dielectric barrier is not always required. Pulse high voltage is
generated either by a mechanical rotary spark gap-type pulse power supply or by a

6 1 Fundamentals of Nonthermal Plasma Technologies

Fig. 1.6 Schematic diagram
of a coaxial-type plasma
reactor

semiconductor pulse power supply. Semiconductors such as insulated gate bipolar
transistor (IGBT) and static induction (SI) thyristor or gap switches are used.

Figure 1.6 shows a coaxial-type plasma reactor in the laboratory. The reactor is
energized by a high-voltage pulse. Figure 1.7 shows voltage, current, and instanta-
neous power waveforms when using an IGBT-type pulse power supply. The diameter
of the plasma reactor is 20 mm, and the distance between electrodes is 10 mm. The
gas used is air, and the discharge average electric power is 11.9 W. The present
method induces a very fast increase in voltage.

1.6 Dielectric Barrier Discharge-Induced Plasmas

The ferroelectric packed-bed method or barrier-type packed-bed plasma reactor is
known to intensify the plasma. Ferroelectric pellets such as barium titanate (BaTiO3)
with a relatively high dielectric constant of ~ 10,000 are used. The power supply may
be combined with a dielectric barrier as in the silent discharge method. Figure 1.8a, b