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Analytical studies of structure and stability of silver nanoparticles in layer-by-layer deposited polyelectrolyte films [Elektronische Ressource] / von Haybat Itani

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150 pages
Analytical Studies of Structure and Stability of Silver Nanoparticles in Layer-by-Layer Deposited Polyelectrolyte Films Dissertation zur Erlangung des Grades Doktor-Ingenieurin der Fakultät für Maschinenbau der Ruhr-Universität Bochum von Haybat Itani aus Beirut, Lebanon Bochum (2010) Dissertation eingereicht am: 28.04.2010 Tag der mündlichen Prüfung: 02.06.2010 Erster Referent: Prof. Dr. Gunther Eggeler Zweiter Referent: Prof. Dr. Guido Grundmeier Doctoral Thesis Haybat Itani Abstract The deposition of polymer films with incorporated metal or oxide nanoparticles lead to new functional properties. Properties such as electronic conductivity, hardness, magnetism, metal-ion release or optical activity etc. can be adjusted by choosing the right combination of metal nanocluster/polymer matrix and density of particles in the matrix. The in-situ formation of Ag-nanoparticles in layer-by-layer (LbL) deposited polyelectrolyte (PE) multilayers is an effective way to form multifunctional composite films that has many applications like increase of corrosion resistance, excellent formability and Ag-release for antibacterial properties.
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Analytical Studies of Structure and
Stability of Silver Nanoparticles
in Layer-by-Layer Deposited
Polyelectrolyte Films




Dissertation
zur
Erlangung des Grades
Doktor-Ingenieurin
der
Fakultät für Maschinenbau
der Ruhr-Universität Bochum
von

Haybat Itani
aus Beirut, Lebanon


Bochum (2010)




































Dissertation eingereicht am: 28.04.2010
Tag der mündlichen Prüfung: 02.06.2010
Erster Referent: Prof. Dr. Gunther Eggeler
Zweiter Referent: Prof. Dr. Guido Grundmeier

Doctoral Thesis Haybat Itani

Abstract

The deposition of polymer films with incorporated metal or oxide nanoparticles lead
to new functional properties. Properties such as electronic conductivity, hardness, magnetism,
metal-ion release or optical activity etc. can be adjusted by choosing the right combination of
metal nanocluster/polymer matrix and density of particles in the matrix. The in-situ formation
of Ag-nanoparticles in layer-by-layer (LbL) deposited polyelectrolyte (PE) multilayers is an
effective way to form multifunctional composite films that has many applications like
increase of corrosion resistance, excellent formability and Ag-release for antibacterial
properties. The layer-by-layer electrostatic assembly technique is a rich versatile and
significantly inexpensive approach to the formation of thin films via alternating adsorption of
positively and negatively charged species from aqueous solution.
The system under-study is consisting of embedded Ag-nanoparticles inside a layer-by-
layer polyelectrolyte film composed of poly(acrylic) acid and poly(allylamine) hydrochloride.
+ Incorporation of the nanoparticles is achieved by diffusion of Ag inside the matrix at
different pH-values and various numbers of adsorbed bilayers. The formation of metallic Ag
nanoparticles is realized by reduction in dilute NaBH aqueous solution. The structure of Ag-4
nanoparticles characterised by local distances and coordination shells around the absorbing
atom was investigated by means of X-ray Absorption Spectroscopy (XAS). The analysis of
the near edge structure reflects the fraction composition of the embedded Ag before, during
and after the reduction process and highlights the nanoparticle formation at the carboxylate
sites. The size and the crystallographic properties of the formed nanoparticles were
investigated by means of TEM while the optical properties were monitored in-situ by means
of UV-VIS Spectroscopy. Transport properties through the PE matrix were also investigated
under different post treatment conditions. In-situ Surface Enhanced Raman spectroscopy
(SERS) and Electro-impedance spectroscopy (EIS) were used to detect diffusion under
different conditions like curing at elevated temperatures and with inclusion of Ag-
nanoparticles.
Additionally, LbL Ag-nanoparticles films are interesting arrays of materials that has many
applications in nanoelectronics and optoelectronic devices. Several works used LbL method
to build up layered structure of Ag-nanoparticles, but the nature of attachment is not well
defined up to now. In this work, the effect of the number of layers on the arrangement of Ag-
nanoparticles is investigated by means of single wavelength ellipsomtery (SWE), and high
resolution atomic force microscopy (HR-AFM). The change of the optical properties is also
monitored by means of UV-VIS spectroscopy (UV-VIS).
ii Doctoral Thesis Haybat Itani

Contents

List of Figures......................................................................................................................vi
List of Tables .......................................................................................................................xi

1 Preface............................................................................................................................2
1.1. Motivation and Objectives ..............................................................................................2
1.2. Scope of the Thesis.........................................................................................................5

2 Fundamentals and Theory...............................................................................................7
2.1. Polyelectrolyte Films ......................................................................................................7
2.1.1. Introduction ............................................................................................................7
2.1.2. Weak Polyelectrolytes.............................................................................................8
2.1.2.1. Poly(acrylic) Acid (PAA)....................................................................................9
2.1.2.1.1. Shifts in the titration curve of PAA under different conditions:..........................13
2.1.2.2. Poly(allylamine) Hydrochloride (PAH) .............................................................15
2.1.2.2.1. Polyelectrolyte Complex ...................................................................................17
2.2. Nanoparticles................................................................................................................21
2.2.1. Properties of Nanoparticles ...................................................................................21
2.2.2. Silver Nanoparticles..............................................................................................24
2.3. Metal Nanoparticles in Polyelectrolyte Multilayers.......................................................25
2.3.1. Introduction ..........................................................................................................25
2.3.2. Interface and Bulk Properties of Nanoparticles in Polyelectrolytes as a Hybrid
System 27
2.4. Transport Phenomenon in Polyelectrolyte Films ...........................................................28
2.4.1. Introduction ..........................................................................................................28

3 Ways and Means...........................................................................................................30
3.1. Thin Film Preparation...................................................................................................30
3.1.1. Functionalizing the Substrate by Means of an Adhesion Promoter.........................30
3.1.1.1. 3-Aminopropyl Trimethoxysilane (APTMS) .....................................................30
3.1.1.2. Poly-ethylenimine (PEI)....................................................................................30
3.1.2. Layer by Layer Deposition Method (LbL).............................................................31
3.1.3. Formation of Silver Nanoparticles by Means of NaBH .........................................33 4
3.2. Analytical Approaches..................................................................................................34
3.2.1. Determination of PE Thickness .............................................................................34
3.2.2. Chemical Composition of the Polyelectrolyte Matrix ............................................35
3.2.3. Morphology of the PE Matrix under different Assembly Conditions .....................36
3.2.4. Optical Properties of the Silver/Polyelectrolyte Nanocomposites...........................36
3.2.5. In-situ UV-VIS Spectroscopy and Electrochemical Impedance Spectroscopy........38
3.2.6. In-situ Surface Enhanced Raman Spectroscopy.....................................................39

4 Theory of Experimental Techniques..............................................................................40
4.1. Ellipsometery................................................................................................................40
iii Doctoral Thesis Haybat Itani

4.2. X-ray Absorption Spectroscopy (XAS) .........................................................................46
4.3. UV-VIS Spectroscopy (UV-VIS)..................................................................................48
4.4. Atomic Force Microscopy (AFM).................................................................................50
4.5. Infra-Red Spectroscopy (IR) .........................................................................................51
4.6. Transmission Electron Microscopy (TEM) ...................................................................52
4.7. Surface Enhanced Raman Spectroscopy (SERS)...........................................................53
4.8. Electrochemical Impedance Spectroscopy (EIS) ...........................................................55

5 Results & Discussions: Tailoring of the Film Properties................................................56
5.1. Determination of the Thickness of the PE Matrix..........................................................56
5.1.1 Film Thickness as a Function of the Number of Bilayers at pH=3.5 ......................56
5.1.2 Film Thickness as a Function of the Number of Bilayers at pH=2.5 ......................60
5.1.3 Film Thickness as a Function of the Assembly pH Value ......................................63
5.2. Determination of the Chemical Composition of the PE Matrix......................................64
5.2.1 Chemical Composition as a Function of the Number of Bilayers ...........................64
5.2.2 Chemical Composition as a Function of the Assembly pH Value ..........................65
5.3. Morphology of the PE Matrix .......................................................................................67
5.3.1 Effect of the Number of Bilayers on the Morphology of the PE Matrix .................67
5.3.2 Effect of the Assembly pH on the Topography of the PE Matrix ...........................69
5.4. Optical Properties of the Silver/ Polyelectrolyte Nanocomposite...................................70
5.4.1 Effect of the Assembly pH on the SPR Band of Ag Nanoparticles in the
Silver/Polyelectrolyte Nanocomposite ..................................................................................70
5.4.2 In-situ Kinetic Reduction of Ag-ions in PE Matrix................................................72
5.4.3 Release of Ag-nanoparticles in Silver/Polyelectrolyte Complex in Acetate Buffer
Solution 74

6 Results & Discussions: XANES Studies of the Formation of Ag-nanoparticles in LbL
deposited polyelectrolyte thin films ......................................................................................77
6.1. Aim ..............................................................................................................................77
6.2. Experimental ................................................................................................................77
6.3. Results and Discussions................................................................................................79
6.4. Conclusions ..................................................................................................................90
6.5. Acknowledgement ........................................................................................................90

7 Results & Discussions: Spectroscopic Studies of the Structure and Stability of LbL
Polyelectrolytes Coatings .....................................................................................................91
7.1. Aim ..............................................................................................................................91
7.2. Experimental ................................................................................................................92
7.3. Results and Discussions................................................................................................94
7.4. Conclusions ................................................................................................................106

8 Results & Discussions: LbL Films with Ag Nanoparticles; How Ag nanoparticles are
arranged on the surface? .....................................................................................................107
8.1. Motivation ..................................................................................................................107
8.2. Experimental ..............................................................................................................108
8.3. Results and Discussions..............................................................................................109
iv Doctoral Thesis Haybat Itani

8.3.1 Study of MPS Layer on Si Substrate Deposited by Means of Gas Transfer..........109
8.3.2 Immobilization of Silver Nanoparticles on MPS Layer........................................111
8.3.2.1 Evaluation of Thickness and Volume Fraction by Means of Single Wavelength
Ellipsometry.......................................................................................................................112
8.3.2.2 Monitoring the Growth of Ag Nanoparticles Layers by Means of UV-VIS
Spectroscopy ......................................................................................................................115
8.3.2.3 Morphology Studies of the Attached Ag Nanoparticles by means of High
Resolution Atomic Force Microscopy.................................................................................117
8.4. Conclusions ................................................................................................................122

9 Overall Conclusions and Outlook................................................................................123

10 References ..................................................................................................................126

11 Appendices .................................................................................................................131
11.1. Abbreviations......................................................................................................131
11.2. List of Symbols...................................................................................................132

Acknowledgement.............................................................................................................134
Publications.......................................................................................................................135
Posters...............................................................................................................................135
Talks..................................................................................................................................136
Curriculum Vitae .............................................................................................................137
v Doctoral Thesis Haybat Itani

List of Figures

Fig.2–1: Structural Formulas of PAA and PAH are shown with their functional groups..........9

Fig.2–2: Titration curves of PAA at different pH variations are presented for different
molecular weights (M ): (□) M =1800, (○) M =5000 and (Δ) M =50000 of PAA. The line w w w w
plot is that of acrylic acid [19]. .............................................................................................11

Fig.2–3: The Influences of the addition of salts of concentration c and hydrophobic layers of
different energies u on the value of pK of PAA are demonstrated[23]..................................14 a

Fig.2–4: The shifts of the pK of PAA are presented in this graph in the presence of weak a
acids and due to many interactions [23]. ...............................................................................15

Fig.2–5: FT-IR spectra of PAH at different pH values as reported by Choi et al.[25] ............16

Fig.2–6: The degree of ionization of PAH are presented at different pH values as evaluated by
many groups [ [25] [26][27]]. ...............................................................................................17

Fig.2–7: The Zeta potential variations of an 8 bilayer film of PAA/PAH with PAA as the
terminating layer under different pH values: pH=3 (▼), pH=5 (■), pH= 7 (▲), pH=9 (●) are
shown. The dotted line is the isoelectric point of PAA solution [29]......................................19

-Fig.2–8: The absorbance ratio of COOH/COO of PAA deposited at different assembly pH
values and as a function of the pH of the transition bath as determined by FT-IR [21]. .........20

Fig.2–9: The difference of energy levels between (a) atoms and (b) clusters (Jellium Model)
are shown [33]......................................................................................................................23

Fig.3–1 a-b: Structural formulas of APTMS and PEI respectively.........................................30

Fig.3–2: Layer-by-layer deposition method steps of the formation of a PE film [37][39]. .....31

Fig.3–3: Schematic sketch of the design of the in-situ cell that combines two experimental
techniques: UV-VIS Spectroscopy and Electrochemical-impedance Spectroscopy................38

Fig. 3–4: Construction of an in-situ cell for performing the in-situ SERS experiment............39

Fig. 4–1 a-b: a Resultant of two added linearly polarized light wave that are in phase; b
General form of an elliptically polarized light wave[62]. ......................................................41

vi Doctoral Thesis Haybat Itani

Fig.4–2 a-b: a represents the typical components of an ellipsometer; b shows the two
phenomena (reflection and refraction) that change the polarization of the incident beam upon
interacting with the sample[63].............................................................................................43

Fig.4–3 a-c: a Multiple scattering mechanism of the propagating photo-electron wave with the
neighboring atoms and the interference mechanism between the scattered wave and the initial
propagating photo-electron wave; b. Modulation of the absorption probability due to XANES
and EXAFS phenomena; c represents the experimental setup of the x-rays absorption
spectroscopy experiment in transmission mode.....................................................................47

Fig. 4–4 :Conventional setup of an atomic force microscope [71]. ........................................50

Fig. 5–1: Model used to fit the experimental data of the SE. It is made up of 3 layers:
substrate, Cauchy layer (PE film) and air..............................................................................57

Fig. 5–2: Measurements of psi and delta with their corresponding fit for samples deposited at
an assembly pH=3.5 and made up of 1, 2, 3, 4 , 5, 6, 7, 8, 9 ,10 bilayers. ..............................58

Fig. 5–3: Plot of the increase of the evaluated thickness with number of deposited bilayers for
samples assembled at pH=3.5. ..............................................................................................59

Fig. 5–4: Zone Model of the PE film. Three distinct zones are clearly shown: Z I, Z II and Z
III[4].....................................................................................................................................60

Fig. 5–5: Model used to fit the PE matrix for samples assembeled at pH=2.5........................61

Fig. 5–6 a-b: a Measured psi and delta with its corresponding fit for samples assembled at
pH=2.5 and made up of 5, 10, 15 and 20 bilayers; b Plot of the evaluated thickness as a
function of number of bilayers..............................................................................................62

Fig. 5–7 a-b: a. Measured psi and delta with their corresponding fit for samples made up of 10
bilayers but assembled at pH=2.5, 3.5 and 4.5; b. Bar plot of the variation of thickness per 10
bilayers with the assembly pH. .............................................................................................63

-1Fig. 5–8: Increase of the underlying area under the 3 bands CH , COOH and COO shows 2
that the mass of the film increases with the increase of the number of bilayers. The spectra are
vertically shifted by 0.005 for clarity. ...................................................................................64

Fig. 5–9: FT-IR spectra of 10 bilayers films deposited on both sides of a Si wafer at pH 2.5,
3.5 and 4.5. The curves are shifted by 0.01 for clarity. An example of Gauss Fit is inserted for
-the bands CH , COO and COOH of sample prepared at pH=2.5...........................................65 2

Fig. 5–10 a-f: a., c. and e. show the topography of samples prepared at pH=3.5 and made up
of 5, 10 and 15 bilayers respectively, b., d. and f. show the analogous phase images of a., c.
and e. respectively. ...............................................................................................................67

vii Doctoral Thesis Haybat Itani

Fig. 5–11 a-d: a. and c. show the topography of 5 bilayers films assembled at pH=3.5 and 4.5
respectively; b. and d. show the phase images analogous to a. and c. respectively.................69

Fig. 5–12: UV-VIS absorption spectra of 10 bilayers films with Ag-nanoparticles deposited
on both sides of glass substrates at pH 2.5, 3.5 and 4.5.The diffusion time of Ag-ions is 1 hr
and the reduction time by means of 1mM NaBH was 30s. ...................................................71 4

Fig. 5–13 a-f: .a, c and e shows the kinetic growth of Ag-nanoparticles prepared in PE
matrices assembled at pH 2.5, 3.5 and 4.5 respectively. The UV-VIS spectra were collected
every 30s after the injection of NaBH ; b, d and f show the sigmoidal growth with its 4
corresponding fitting for the kinetic growth of Ag-nanoparticles assembled at pH 2.5, 3.5 and
4.5 respectively.....................................................................................................................73

Fig. 5–14 a-f: a., c. and e. show the decrease of the UV-VIS absorption curves underlying
areas with immersion time of samples prepared at pH values: 2.5, 3.5 and 4.5 respectively; b.,
d. and f. show the plot the SPR height (Abs. ) against time for samples prepared at pH max
values 2.5, 3.5 and 4.5 respectively.......................................................................................75

Fig. 6–1: UV-Vis absorption spectra of 10 bilayers films with Ag-nanoparticles deposited on
both sides of the glass substrates at pH 2.5, 3.5 and 4.5. The diffusion time of Ag-ions into the
polyelectrolyte network is 1 hr and the reduction time by means of 1 mM NaBH was 30 s. 4
The inserted cross section TEM image shows the formation of Ag-nanoparticles by the
reducing agent NaBH . .........................................................................................................81 4

Fig. 6–2 a-c: (a) UV-Vis absorption spectra of Ag-nanoparticles embedded in a sample of 10
bilayers film deposited on both sides of glass substrates at pH 2.5 as a function of exposure
time, as indicated. The diffusion time of Ag-ions into the polyelectrolyte network is 1 hr
without any successive reduction by means of NaBH . The sample was subjected to ambient 4
UV-radiation and the formation of Ag-nanoparticles appeared clearly as a pronounced
Plasmon resonance after a few days; (b) Time dependence of the area under the SPR-peak of
the UV-Vis spectra of samples prepared at pH values of 2.5 (solid line), 3.5 (long dashed line)
and 4.5 (short dashed line); (c) Time dependence of the FWHM of the SPR-peak of the UV-
Vis spectra of samples prepared at pH values of 2.5 (solid line), 3.5 (long dashed line) and 4.5
(short dashed line). ...............................................................................................................83

Fig. 6–3 a-b: a. Changes in the XANES region for samples deposited at pH=3.5 and reduced
at different intervals of time from 0 to 60 min; b. XANES of the possible reference
compounds that could be used in the LC-fit of the XANES of the samples. ..........................85

Fig. 6–4 a-b: a. LC-fit of the XANES region of a sample deposited at pH=3.5, diffusion time
t =1hr and no reduction with the shown XANES of reference compounds; b. Change of the d
XANES between a non-reduced sample and a 60min reduced sample with their corresponding
LC-fit. ..................................................................................................................................86

viii Doctoral Thesis Haybat Itani

Fig. 6–5: Fractional composition of the embedded Ag in the LbL-film prepared at pH = 3.5 as
a function of reduction time. The fractional composition was determined by means of a linear
combination analysis of Ag K-edge XANES spectra.............................................................88

Fig. 7–1 a-c: Molecular structure of PAA and PAH a., and 2-mercaptobenzothiazole (2MBI)
b., amidation reaction during curing at elevated temperatures c.............................................95

Fig. 7–2 a-b: SERS measurements of 2MBI diffusion through the PE film at different times
after contact with 2MBI solution a.; 2MBI spectrum on bare Ag surface and spectrum after
120 min of 2MBI diffusion b.. ..............................................................................................96

Fig. 7–3 a-d: SERS measurement of MBI adsorption on pure SERS substrate a.; PE covered
SERS substrate b.; PE containing Ag nanoparticles on SERS substrate c.; PE cured at 180°C
on SERS substrate d.. ...........................................................................................................97

Fig. 7–4: FT-IR spectroscopy in 80° reflection mode of 2MBI on pure SERS substrate, PE
film, PE film after MBI diffusion and 180°C cured PE film after 2MBI diffusion...............100

Fig. 7–5: FT-IR spectra showing variation of the chemical composition of PE films with
curing at 130°C, 150°C, 180°C and 200°C. The spectrum at room temperature (RT) is given
as a reference......................................................................................................................101

Fig. 7–6 a-b: a. Bode plots of cured PE films at RT, 130°C, 150°C, 180°C, 200°C and ITO
substrate as reference after 5 min of immersion in borate buffer; b. Bode plot of PE film cured
at 180°C. ............................................................................................................................102

Fig. 7–7: Capacitance evaluated at 1Hz for cured samples ( RT, 130°C, 150°C, 180°C. 200°C)
and PE films containing Ag nanoparticles in borate buffer as a function of time. ................105

Fig. 8–1 1-3: 1. Structural formula of MPS showing two functional groups; 2. Tof-SIMS
spectra indicating the deposition of MPS by means of gas transfer; 3. model used for SWE
with its corresponding measurement...................................................................................110

Fig. 8–2. Prepared Ag NP are spherical in shape and their diameter varies between 2 and 5 nm.
...........................................................................................................................................111

Fig. 8–3 a-b: (a) &(b) possibility of the formation of Ag NP LbL layers; (c) shows the model
used to evaluate the thickness and volume fraction of Ag NP in the LbL films. ..................113

Fig. 8–4 a-d: a & b SWE measurements with its fit for samples with host MPS-G and MPS-L
respectively; c & d Δ-ψ trajectory of the samples at the Brewster angle of Si substrate to show
coverage of the substrate with every dipping cycle with starting layer MPS-G and MPS-L
respectively. .......................................................................................................................114

Fig. 8–5 a-b: a & b show the volume fraction % of Ag NP for samples made up of 1,2 and 3
layers of Ag NP with hosting matrices MPS-L or air and MPS-G or air respectively...........115
ix

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