«PREPARATION AND CHARACTERIZATION OF POLYMER COMPOSITES CONTAINING GOLD NANOPARTICLES a dissertation submitted to the department of chemistry and the ...»
PREPARATION AND CHARACTERIZATION
OF POLYMER COMPOSITES CONTAINING
a dissertation submitted to
the department of chemistry
and the graduate school of engineering and science
of bilkent university
in partial fulfillment of the requirements
for the degree of
doctor of philosophy
I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of doctor of philosophy.
Prof. Dr. Seﬁk S¨zer (Advisor) ¸ u I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of doctor of philosophy.
Prof. Dr. Erdal Bayramlı I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of doctor of philosophy.
Assoc. Prof. Dr. Margarita Kantcheva ii I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of doctor of philosophy.
Assist. Prof. Dr. Erman Beng¨ u I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality, as a dissertation for the degree of doctor of philosophy.
Assist. Prof. Dr. Co¸kun Kocaba¸ s s
Approved for the Institute of Engineering and Science:
Prof. Dr. Levent Onural Director of the Institute iii ABSTRACT
PREPARATION AND CHARACTERIZATION OF POLYMER COMPOSITES
CONTAINING GOLD NANOPARTICLESEDA YILMAZ Ph.D. in Chemistry Supervisor: Prof. Dr. Şefik Süzer September, 2011 In this study, light-assisted synthesis of gold nanoparticles in polymer films is demonstrated and characterization of gold nanoparticle-polymer composites using various techniques is shown. There are various methods introduced for the synthesis of gold nanoparticles in solution and their integration to the polymer films afterwards. However, synthesizing gold nanoparticles directly inside the polymer matrix is more advantageous for the production of polymer-nanoparticle composites.
An advantage of synthesizing gold nanoparticles within polymer films is the opportunity of photo-patterning. Films having patterns made of regions with and without gold nanoparticles can be produced, using masks designed to cut off the radiation at desired places. Such patterned films were investigated with scanning electron microscope (SEM) and dark regions between irradiated regions and masked regions were observed. These dark regions are shown to be “ion depleted regions”, where gold ions diffuse through irradiated regions during the irradiation. These regions of about 10 m width, suggests a very large distance for gold ions to diffuse through a rigid matrix like Poly(methyl methacrylate)(PMMA), which is very interesting. Supporting evidence for the existence of these regions was obtained from fluorescence studies with Rhodamine 6G molecule and x-ray electron spectroscopy (XPS).
The observations made through the formation of ion depleted regions can be used to estimate the diffusion constant of gold ions inside the PMMA matrix. Also the presence of ion depleted regions indicate the stability of photo-patterns created on the polymer film against IV smearing during light exposure after the production, by setting an upper limit to the critical feature size.
During the characterization of gold nanoparticle-polymer composites, the electrical properties of PMMA with and without gold nanoparticles were investigated using charge resolved XPS, while applying external bias to the films with and without gold nanoparticles to probe the charging properties of the films. An enhancement of conductivity of PMMA films containing gold nanoparticles was observed using this technique. Additionally charge resolved XPS technique was also used to determine the charge storage characteristics of the polymer surfaces, which is important for the identification of charging mechanisms during contact and other electrification processes. It was shown that the PMMA surface is very susceptible to negative charging and even native negative charges on the PMMA surface can be observed prior to any treatment. Also when the surface is charged carbon and oxygen atoms of the carbonyl and methoxy groups of PMMA were observed to behave differently from the backbone of the polymer, which shows the chemical specificity of the charge accumulating spots on the surface.
Keywords: Gold nanoparticle, PMMA, XPS, Charge resolved XPS, Photo-patterning, Ion depleted region, Contact electrification
Bu çalışmada altın nanoparçacıklarının polimer filmleri içerisinde ışık yardımıyla sentezlenmesi ve çeşitli teknikler kullanılarak altın nanoparçacığı-polimer kompositlerinin karakterizasyonu gösterilmektedir. Altın nanoparçacıklarının çözelti fazında sentezini ve sonradan polimer filmlerine bütünleştirilmesini gösteren başka çalışmalarda mevcuttur. Fakat bu uygulamalara nazaran altın nanoparçacıklarının polimer filmleri içerisinde sentezlenmesi, polimer-nanoparçacık kompositlerinin üretimi açısından daha basit ve avantajlıdır.
Altın nanoparçacıklarının polimer filmleri içinde sentezlenmesinin bir avantajı, bu tekniğin ışıkla desenleme uygulamalarına imkan sağlamasıdır. Bu yöntemle UV ışığını istenen bölgelerde kesen maskeler kullanılarak, polimer içinde altın nanoparçacığı içeren ve içermeyen bölgelerden oluşan desenler oluşturulabilir. Bu şekilde oluşturulan desenli filmlerin taramalı elektron mikroskobu ile incelenmesi sırasında, maskelenmiş ve radyasyona maruz bırakılmış bölgeler arasında mikroskopta koyu gözüken bölgeler tespit edilmiştir. Bu koyu bölgeler “İyondan arındırılmış bölgeler” olarak adlandırılmış olup oluşumları sırasında altın iyonlarının radyasyona maruz bırakılmış bölgelere doğru hareket ettiği düşünülmektedir.
İyonların bu bölgeleri oluştururken katı bir polimer filmi içerisinde 10 µm gibi uzun bir mesafe kat etmesi ilgi çekicidir. Bu bölgelerin varlığı ile alakalı destekleyici kanıtlar Rhodamine 6G molekülünü kullanan floresans çalışmalarından ve x-ışını fotoelektron spektroskopisinden (XPS) elde edilmiştir. İyondan arındırılmış bölgelerde yapılan incelemelerden yola çıkılarak, altın iyonlarının poli(metil metakrilat) (PMMA) filmleri VI içerisindeki hareket kabiliyetlerine ait difüzyon katsayısı hesaplanabilir. Bunun yanı sıra iyondan arındırılmış bölgelerin varlığı, daha dayanıklı, ışıkla temas sonucu kusma yapmayan desen oluşumunda çok önemlidir.
Altın nanoparçacığı-polimer kompositlerinin karakterizasyonu bağlamında, yük çözümlemeli XPS tekniği ile altın nanoparçacığı içeren ve içermeyen PMMA filmleri, dışarıdan voltaj uygulanarak incelenmiştir. Bu çalışmalar sonucunda altın nanoparçacığı içeren PMMA filmlerinin iletkenliklerinin arttığı gözlemlenmiştir. Buna ek olarak, yük çözümlemeli XPS tekniği ayrıca polimer yüzeylerinin yük toplama özelliğinin incelenmesi için kullanılmıştır.
Bu özellik yalıtkan malzemelerin temasla elektriklenmesi olayının aydınlatılması için büyük önem taşımaktadır. Bu çalışmalarda PMMA yüzeyinin eksi yükleri toplamaya çok yatkın olduğu gösterilmiş ayrıca yüzeyde hiçbir etki olmaksızın yerel eksi yüklerinde bulunduğu gözlemlenmiştir. Ayrıca yüzey yüklü olduğu durumlarda PMMA‟nın karbonil ve metoksi gruplarının polimerin iskeletinden daha farklı davrandığı görülmüştür. Bu durum özellikle yük toplama noktalarının kimyasal özelliklerinin tayini için önem arz etmektedir.
Anahtar kelimeler: Altın nanoparçacığı, PMMA, XPS, Yük çözümlemeli XPS, Işıkla desenleme, İyondan arındırılmış bölge, Temasla elektriklenme.
I would like to express my deepest gratitude to Prof. Dr. Şefik Süzer for his excellent supervision and his support during 7 years starting from my undergraduate to my Ph.D.
graduation. I would like to thank Dr. Gülay Ertaş for always answering my questions and helping me in every possible way. I‟m also grateful to my committee members for their valuable contributions during the preparation on this thesis.
I‟m indebted to my husband and my family for all their support and self-sacrifice on my behalf.
I also would like to thank my present and past groups members, Hikmet Sezen, İlknur Tunç, Ivalina Avromova, C. Pinar Cönger, Hacı Osman Güvenç and Merve Taner, for their support.
Finally, I would like express my gratitude to TÜBİTAK for the financial support during my studies.
Table of Contents
List of Figures
List of Tables
1.1 Applications of Gold Nanoparticles
1.1.1 Gold Nanoparticles in Electronics
1.1.2 Gold Nanoparticles in Catalysis
1.1.3 Gold Nanoparticles in Biotechnology
1.1.4 Gold Nanoparticles in Characterization
1.2 Applications of Nanoparticle-Polymer Composites
1.3 Synthesis of Nanoparticles
1.3.1 Synthesis of Gold Nanoparticles in the Solution Phase
1.3.2 Synthesis of Nanoparticles in Polymer Matrix
1.4 Advantages of Poly(methyl methacrylate) as a Synthesis Medium
1.5 Photo-Patterning of Polymer Composites
1.6 Ultraviolet-Visible Spectroscopy
1.6.1 Surface Plasmon Resonance Band of Gold Nanoparticles
1.7 X-Ray Photoelectron Spectroscopy
1.7.1 Using Charging as a tool in XPS
1.8 Contact Electrification of Insulating Materials
1.9 Objective of the Study
2.2 Preparation of Samples
3 Results and Discussion
3.1 Light Induced Production of Gold Nanoparticles
3.2 Photo-patterning and Investigation of Ion Depleted Regions
3.3 Effect of Gold Nanoparticles on the Dielectric Properties of PMMA
3.4 Extra electrons on the PMMA Surface: Pendant Groups are Affected More than Skeleton Carbons
5 List of Abbreviations
7.2 Conference Presentations
Figure 1.1 Evolution of electronic states of a metal from molecule to bulk
Figure 1.2 Schematic representation UV radiation induced, reduction of Au3+ ions to Au0 atoms and nucleation and growth of Au nanoparticles in polymer matrix
Figure 1.3 A UV-Vis spectrum showing the dependency of SPR band to the particle size.
... 17 Figure 1.4 Schematic representation of XPS measurement
Figure 1.5 Schematic representation of angle resolved XPS measurement.
Figure 1.6 Shifting of the XPS peaks due to +/- 10 V DC bias in a conducting sample.
........ 22 Figure 1.7 Schematic representation of contact electrification.
Figure 2.1 Schematic representation of spin coating procedure.
Figure 2.2 Illustration of experimental setup for the SQW voltage applied measurement on PMMA films.
Figure 3.1 UV-Vis Spectrum of PMMA/Au film; reduction of Au3+ and nucleation and growth of Au NPs
Figure 3.2 Effect of heating and addition of Pt ions on NP formation vs.
Au3+ reduction. It „s seen that both heating and Pt ions addition increases NP formation without affecting reduction rate.
Figure 3.3 Structure of benzophenone
Figure 3.4 UV-Vis spectra of PMMA/Au films with and without benzophenone taken in appropriate time intervals
Figure 3.5 UV-Vis spectra of PVA/Ag films with and without benzophenone taken in appropriate time intervals
Figure 3.6 IR spectra of Au-PVA and PVA films taken after appropriate irradiation times.
.. 39 Figure 3.7 Reduction of Au3+ in PMMA by different wavelengths of UV-Vis radiation........ 40 Figure 3.8 Reduction of Au3+ in PVA by different wavelengths of UV-Vis radiation............ 41 Figure 3.9 Graph summarizing the reducing effects of different wavelengths of light on PVA and PMMA.
Figure 3.10 Light microscope image of the photo-pattern produced on Au-PMMA film.
Figure 3.12 Secondary electron (left) and backscattered electron (right) images of a photopatterned Au-PMMA film
Figure 3.13 Light microscope image of photopattern produced on Au-PMMA film by 200 μm x 200 μm mesh, the film was irradiated for another 24 hours after the mask was removed.
... 46 Figure 3.14 SEM image of the photopatterned Au-PMMA film after second UV treatment.. 46 Figure 3.15 Illustration of ion migration during irradiation and the ion depleted region at the border, after mask is removed and after second UV treatment.
Figure 3.16 Fluorescence microscope image of a photo-patterned Au/R6G/PMMA film.
..... 49 Figure 3.17 Fluorescence images of photo-patterned (a) Au-PMMA and (b) PMMA films with R6G taken by fluorescence microscope.
Figure 3.18 Fluorescence microscope images of PMMA with gold and R6G, the middle of which contains that of only R6G film overlapped.
Figure 3.19 Overlapped images of SEM and fluorescence microscope of the same sample.
.. 52 Figure 3.20 Fluorescence images of PMMA film with Au and R6G irradiated for 30 minutes, 1 hour and 24 hours. Inlet: XPS line scans of the Au4f peak intensity
Figure 3.21 Photo-patterned PVA film containing Au nanoparticles and R6G, left hand-side shows SEM image right hand-side shows fluorescence image.
Figure 3.22 The scheme of samples used for XPS measurement