plasma polymerized hydrogel thin films for applications in sensors and actuators

158 Pages·2006·1.89 MB·English

PLASMA POLYMERIZED HYDROGEL THIN FILMS FOR
APPLICATIONS IN SENSORS AND ACTUATORS

A Dissertation
Presented to
The Academic Faculty

by

Prabhakar A. Tamirisa

In Partial Fulfillment
of the Requirements for the Degree
Doctor of Philosophy in the
School of Chemical & Biomolecular Engineering

Georgia Institute of Technology
December 2006
PLASMA POLYMERIZED HYDROGEL THIN FILMS FOR
APPLICATIONS IN SENSORS AND ACTUATORS

Approved by:

Dr. Dennis W. Hess, Advisor Dr. J. Carson Meredith
School of Chemical & Biomolecular School of Chemical & Biomolecular
Engineering Engineering
Georgia Institute of Technology Georgia Institute of Technology

Dr. Clifford L. Henderson Dr. Mark R. Prausnitz
School of Chemical & Biomolecular School of Chemical & Biomolecular
Engineering Engineering
Georgia Institute of Technology Georgia Institute of Technology

Dr. William D. Hunt
School of Electrical & Computer
Engineering
Georgia Institute of Technology

Date Approved: September 05, 2006
ACKNOWLEDGEMENTS

First, I would like to thank my research advisor, Prof. Dennis Hess for providing
valuable guidance, financial support, and encouraging creative ideas and critical thinking
throughout my stay at Georgia Institute of Technology. I also wish to thank my
committee members Prof. Clifford Henderson, Prof. William Hunt, Prof. Carson
Meredith, and Prof. Mark Prausnitz for their suggestions, feedback, and critique of my
work. I thank Prof. William Hunt and Dr. Sang-Hun Lee, School of Electrical &
Computer Engineering for collaborating on the development of the electrophoretic
immobilization procedure and surface acoustic wave sensors. I wish to thank Prof.
Clifford Henderson for kindly allowing the use of many analytical instruments. Most of
this work would not have been possible without access to the thin film characterization
equipment. I would like to thank Prof. Y. C. (Jerry) Jean, Dept. of Chemistry, University
of Missouri-Kansas City, for kindly agreeing to conduct positron annihilation studies on
the plasma deposited hydrogel films, and assisting in the interpretation of the results. I
would also like to thank Prof. Yulin Deng for kindly allowing the use of a contact angle
measurement apparatus at the Institute of Paper Science and Technology. I thank Dr.
Jere Koskinen, formerly of the Institute of Paper Science and Technology, for
collaborating on the initial stages of this project, and providing financial support. I also
thank Ms. Gloria Beale for processing numerous purchase orders, Mr. Scott Fowler for
helping me troubleshoot the RF power system, and Mr. Johnafel Crowe for training me
on the confocal laser scanning microscope and providing several useful suggestions.

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Thanks to Dr. Sudeep Vaswani, former member of Prof. Hess’ group, for training me on
the operation of the plasma reactors. I would like to acknowledge several members (both
former and present) of Prof. Hess’ research group for sharing their valuable insights on
my experiments during and outside of the group meetings, training me on various
analytical instruments, and their camaraderie (in no particular order): Dr. Matthew
Spuller, Dr. Ebony Mays, Dr. Jie Diao, Dr. Satyanarayana Myneni, Dr. Christopher
Timmons, Dr. Qian Luo, Dr. Galit Levitin, Ashwini Sinha, Lingbo Zhu, Ingu Song,
Yonghao Xiu, Gelareh Shakourian, Shantanu Pathak and Bala Balakrishna. I thank Mr.
Safdar Ali, for working with me to study the stability of NIPAAm thin films. In addition,
I would like to thank Dr. Desmond Stubbs, Mr. Tony Dickherber, and Mr. Christopher
Corso, members of the ‘maglab’, for their valuable comments and support. I would also
like to thank Mr. Daniel Hallow for loaning a DC power source.

I also thank Troy, Sean, David, Len, and Murali, for their friendship and support during
my stay in Atlanta. Finally, I thank my parents for their love, encouragement, and
precious support over the years.

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TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS iii
LIST OF TABLES vii
LIST OF FIGURES viii
SUMMARY xi
CHAPTER
1 INTRODUCTION 1
2 BACKGROUND 5
2.1 Plasma polymerization 5
2.2 Hydrogels 15
2.3 Applications in sensors and actuators 21
3 SYNTHESIS AND CHARACTERIZATION 29
3.1 Introduction 29
3.2 Experimental Section 31
3.3 Results and Discussion 36
3.3.1 Infrared Spectroscopy Characterization of Hydrogel Films 38
3.3.2 Thermoresponsive Properties of Hydrogel Films 44
3.4 Conclusions 49
4 WATER AND MOISTURE UPTAKE CHARACTERISTICS 51
4.1 Introduction 51
4.2 Experimental Section 55
4.3 Results and Discussion 58
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4.3.1 Water uptake measurements 59
4.3.2 Moisture uptake measurements 66
4.4 Conclusions 73
5 MICROSTRUCTURE CHARACTERIZATION 74
5.1 Introduction 74
5.2 Experimental Section 78
5.3 Results and Discussion 79
5.4 Conclusions 85
6 SUMMARY AND RECOMMENDATIONS 87
6.1 Summary 87
6.2 Recommendations 89
APPENDIX A: ELECTROPHORETIC IMMOBILIZATION AND SENSOR
DEVELOPMENT 91
APPENDIX B: STABILITY STUDIES 109
REFERENCES 126
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LIST OF TABLES
Page
Table 2.1: Examples of polymers that exhibit LCST behavior in aqueous solutions1 16

Table 3.1: VASE results of NIPAAm films deposited on silicon 37

Table 3.2: FTIR band assignments for NIPAAm films deposited on silicon 41

Table 5.1: Thickness and refractive index of plasma polymerized NIPAAm films from
variable angle spectroscopic ellipsometry 81

Table 5.2: Fitted parameters (from VEPFIT2) for DBES plots shown in Figure 5.1
83

Table B.1: Thickness values of NIPAAm films exposed to DI water 113

Table B.2: Thickness values of NIPAAm films exposed to PBS 114

Table B.3: Thickness values of NIPAAm films exposed to TAE 115

Table B.4: Comparison of Amide I and II bands in the FTIR spectra 123

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LIST OF FIGURES
Page
Figure 2.1: Schematic of the competitive ablation and polymerization (CAP)
mechanismof plasma polymerization: (1) Ablation of the monomer to form
reactive species in the plasma phase; (2) Adsorption of reactive species on
substrate; (3) Heterogeneous reaction with substrate to form plasma polymer
film; (4) Desorption of unreacted species from substrate25 8

Figure 2.2: Relationship between basic plasma parameters and plasma-surface
interaction parameters3 11

Figure 3.1: Schematic of the capacitively coupled, parallel plate plasma reactor used to
deposit NIPAAm thin films 33

Figure 3.2: FTIR spectra of NIPAAm films deposited on silicon at 133.3 Pa at 150 °C,
175 °C and 200 °C; 30 W rf power 39

Figure 3.3: FTIR spectra of NIPAAm films deposited on silicon at 93.3 Pa at 120 °C,
150 °C, 175 °C and 200 °C; 30 W rf power 40

Figure 3.4: Contact angles of plasma polymerized NIPAAm on silicon surface
deposited at (a) 120 ºC, 93.3 Pa, (b) 150 ºC, 133.3 Pa. RF power was 30 W
for all samples, (c) 150 ºC, 93.3 Pa, and (d) 175 ºC, 133.3 Pa. RF power
was 30 W for all samples 45

Figure 4.1: Variation of –Δf (top) and ΔD (bottom) with temperature for NIPAAm films
prepared using process condition B (Substrate temperature = 120 ºC;
Reactor pressure = 93.3 Pa) 61

Figure 4.2: Variation of –Δf (top) and ΔD (bottom) with temperature for NIPAAm films
prepared using process condition C (Substrate temperature = 175 ºC;
Reactor pressure = 133.3 Pa) 62

Figure 4.3: Variation of –Δf (top) and ΔD (bottom) with temperature for NIPAAm films
prepared using process condition D (Substrate temperature = 175 ºC;
Reactor pressure = 93.3 Pa) 63

Figure 4.4: Variation of –ΔD/Δf (1E-6) with temperature for NIPAAm films prepared
using different reactor conditions 65

Figure 4.5: Moisture absorption kinetics from ambient air (~ 40% relative humidity) for
NIPAAm film prepared using: (a) process condition B (Substrate
temperature = 120 ºC; Reactor pressure = 93.3 Pa); (b) process condition C
viii
(Substrate temperature = 175 ºC; Reactor pressure = 133.3 Pa – top); (c)
process condition D (Substrate temperature = 175 ºC; Reactor pressure =
133.3 Pa – bottom) 67

Figure 4.6: Comparison of moisture uptake capacities of NIPAAm films prepared using
different reactor conditions, through swelling ratio, Q 70

Figure 5.1: Interactions of positron and positronium with condensed matter4 75

Figure 5.2: A schematic diagram of the slow positron beam at the University of
Missouri-Kansas City. A: 50 mCi 22Na positron source, B: W-mesh
moderator, C: magnetic field (75 G) coils, D: E X B filter, E: positron
accelerator and electric insulator, F: correcting magnets, G: gas inlet, H:
positron lifeline system for PAL, I: turbo molecular pump, J: samples, K:
sample manipulator, L: cryo pump, M: Ge solid state detector, N: PAL
detector5 79

Figure 5.3: Variation of S parameter as a function of positron incident energy in plasma
polymerized NIPAAm thin films prepared under different process
conditions: (a) 0 < positron incident energy < 30 keV (top) (b) 0< positrons
incident energy < 5 keV (bottom) 80

Figure 5.4: Values of S parameter of the second layer and refractive index of plasma
polymerized NIPAAm films prepared under different reactor conditions
84

Figure A.1: Schematic of the electrophoretic immobilization set up (not drawn to scale)
97

Figure A.2: Frequency response of SAW devices after NIPAAm deposition (---), after
anti-FITC immobilization (---), and after exposure to uranine vapor (---); (a)
Electrophoretic immobilization at 5 V (top); (b) Electrophoretic
immobilization at 1 V (bottom); (c) No anti-FITC immobilization 100

Figure A.3: Frequency response of SAW devices after NIPAAm deposition (---), after
anti-FITC immobilization (---), and after exposure to uranine vapor (---); (a)
Electrophoretic immobilization at 0.5 V for 15 min (top); (b) Electrophoretic
immobilization at 0.5 V for 10 min(bottom); (c) NIPAAm film - no
electrophoretic immobilization (top); (d) Blank SAW device – No NIPAAm
film, no electrophoretic immobilization (bottom) 105

Figure A.4: CLSM images: (a) Anti-FITC containing NIPAAm film (0.5 V for 15 min);
(b) Anti-FITC containing NIPAAm film (0.5 V for 10 min); (c) Blank SAW
device – no hydrogel film; (d) Hydrogel coated SAW device – no anti-FITC
107

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Figure B.1: Thickness of NIPAAm films prepared under different reactor conditions as a
function of exposure to DI water 111

Figure B.2: Thickness of NIPAAm films prepared under different reactor conditions as a
function of exposure to PBS solution 112

Figure B.3: Thickness of NIPAAm films prepared under different reactor conditions as a
function of exposure to TAE solution 112

Figure B.4: FTIR spectra of NIPAAm films exposed to DI water showing the amide I
and II regions 120

Figure B.5: FTIR spectra of NIPAAm films exposed to PBS solution showing the amide
I and II regions 121

Figure B.6: FTIR spectra of NIPAAm films exposed to TAE solution showing the amide
I and II regions 122

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