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Internal structure of polyelectrolyte multilayers on nanometer scale [Elektronische Ressource] / Oxana Ivanova

155 pages
INTERNALSTRUCTUREOFPOLYELECTROLYTEMULTILAYERSONNANOMETERSCALEI n a u g u r a l d i s s e r t a t i o nzurErlangung des akademischen Grades einesDoktors der NaturwissenschaftenderMathematisch-Naturwissenschaftlichen Fakult¨atderErnst-Moritz-Arndt-Universit¨at Greifswaldvorgelegt vonOxana Ivanovageboren am 06. April 1980in Sankt-Petersburg (Russland)-Greifswald, 2010 -Dekan: Prof. Dr. Dr. Klaus Fesser1. Gutachter: Prof. Dr. Christiane A. Helm2. Gutachter: Prof. Dr. Monika Sch¨onhoffTag der Promotion: 15. Oktober 2010Ich m¨ochte mich ganz herzlich bei allen Mitarbeitern des Instituts fur¨ Physikfur¨ zahllose fachverwandte sowie fachfremde Unterstutzung¨ bedanken.ContentsI Introduction to the Field of Research 71 Introduction 91.1 Polyelectrolytes and their Properties . . . . . . . . . . . . . . . . . . . . . . 91.2 Layer-by-Layer Assembly of Polyelectrolytes . . . . . . . . . . . . . . . . . . 101.3 Polyelectrolyte Multilayers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131.4 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 Physical Background 172.1 Electrostatic and Secondary Interactions . . . . . . . . . . . . . . . . . . . . 172.1.1 Electrostatic Interactions: Electric Double Layer . . . . . . . . . . . . 182.1.2 Effect of Salt on Formation of PEMs . . . . . . . . . . . . . . . . . . 212.1.3 Classification and Range of Intermolecular Forces . . . . . . . . . . . 222.1.
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INTERNALSTRUCTURE
OFPOLYELECTROLYTEMULTILAYERS
ONNANOMETERSCALE
I n a u g u r a l d i s s e r t a t i o n
zur
Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
der
Mathematisch-Naturwissenschaftlichen Fakult¨at
der
Ernst-Moritz-Arndt-Universit¨at Greifswald
vorgelegt von
Oxana Ivanova
geboren am 06. April 1980
in Sankt-Petersburg (Russland)
-Greifswald, 2010 -Dekan: Prof. Dr. Dr. Klaus Fesser
1. Gutachter: Prof. Dr. Christiane A. Helm
2. Gutachter: Prof. Dr. Monika Sch¨onhoff
Tag der Promotion: 15. Oktober 2010Ich m¨ochte mich ganz herzlich bei allen Mitarbeitern des Instituts fur¨ Physik
fur¨ zahllose fachverwandte sowie fachfremde Unterstutzung¨ bedanken.Contents
I Introduction to the Field of Research 7
1 Introduction 9
1.1 Polyelectrolytes and their Properties . . . . . . . . . . . . . . . . . . . . . . 9
1.2 Layer-by-Layer Assembly of Polyelectrolytes . . . . . . . . . . . . . . . . . . 10
1.3 Polyelectrolyte Multilayers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2 Physical Background 17
2.1 Electrostatic and Secondary Interactions . . . . . . . . . . . . . . . . . . . . 17
2.1.1 Electrostatic Interactions: Electric Double Layer . . . . . . . . . . . . 18
2.1.2 Effect of Salt on Formation of PEMs . . . . . . . . . . . . . . . . . . 21
2.1.3 Classification and Range of Intermolecular Forces . . . . . . . . . . . 22
2.1.4 Temperature Effect: Hydrophobic Interactions . . . . . . . . . . . . . 23
II Materials and Methods 25
3 and Sample Preparation 27
3.1 Chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2 Fabrication of Multilayered Nanofilms . . . . . . . . . . . . . . . . . . . . . . 29
4 Characterization Methods 33
4.1 X-ray and Neutron Reflectivity . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.1.1 Basic Principles of X–ray and Neutron Reflection . . . . . . . . . . . 35
4.1.2 Reflection from Ideally Smooth & Rough Interfaces . . . . . . . . . . 37
4.1.3 Refractivity Set–up . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2 UV-Vis Absorption Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2.1 Interaction of Light with Matter . . . . . . . . . . . . . . . . . . . . . 43
4.2.2 Beer-Lambert Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.3 Optical Properties of Metallic Nanoparticles . . . . . . . . . . . . . . 44
4.3 Atomic Force Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.3.1 Basic Principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
4.3.2 Tip Convolution and Surface Reconstruction . . . . . . . . . . . . . . 51
5 Data analysis 53
5.1 Reflectivity Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
5.1.1 Dynamic Approximation (Parratt Algorithm) . . . . . . . . . . . . . 53
5.1.2 Kinematic for Superlattice PEM Structure . . . . . . 55
5III Results 59
6 Immobile Water and Proton–Deuterium Exchange 61
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
6.2 Swelling of Polyelectrolyte Multilayers . . . . . . . . . . . . . . . . . . . . . 62
6.3 Determination of Tightly Bound Immobile Water . . . . . . . . . . . . . . . 66
6.4 Proton–Deuterium Exchange in PAH Monomers . . . . . . . . . . . . . . . . 81
6.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
6.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7 Thickness and Composition of PEMs 87
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.2 Effect of Temperature on PEMs . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.2.1 The Onset of the Temperature Effect . . . . . . . . . . . . . . . . . . 89
7.2.2 Influence of Temperature during Formation of PEMs . . . . . . . . . 92
7.2.3 of Temp after Preparation of . . . . . . . . . 95
7.3 Effect of Ions: Hofmeister Series . . . . . . . . . . . . . . . . . . . . . . . . . 102
7.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
8 Tuning of Lateral Structure 109
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8.2 Silver Nanoparticles Embedded into PEM . . . . . . . . . . . . . . . . . . . 110
8.2.1 Optical Properties of Silver Monolayer . . . . . . . . . . . . . . . . . 112
8.2.2 Aggregation of Silver Nanoparticles . . . . . . . . . . . . . . . . . . . 115
8.2.3 Rearrangement of beneath a PEM . . . . . . . . . . . . 120
8.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
8.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
IV Thesis Summary 129
Summary 131
Symbols and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Curriculum Vitae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Publications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Conference Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155Part I
Introduction to the Field of Research
7Chapter 1
Introduction
The idea to create materials with specific properties is as old as mankind. Besides the
knowledge how to create the material, the knowledge how to manipulate it in a proper
way is essential. This requires deep understanding of background physics and chemistry,
especiallyofsurfacephenomenaatthenanoscale. Developmentofnewexperimentalmethods
makesthenano–cosmosaccessibleasatoolforadvancedmaterials. Increasingimportanceof
functionalized surfaces and nanocomposite systems places their properties in the foreground
of scientific and technical interest. Flexible composition control of such systems can be
gained by use of multilayer technology.
The polyelectrolyte multilayers are a new class of organic thin films that allow precise
control of film thickness within a few nanometers. Furthermore, it is possible to manipulate
molecular architectures composed of a number of functional materials and study physical
phenomena on the molecular level.
1.1 Polyelectrolytes and their Properties
Thetermpolyelectrolytedenotesaclassofmacromolecularcompoundsorpolymerswith
high molecular weight whose repeating units bear an electrolyte group that dissociates in a
suitable polar solvent (usually water) and acquires a large number of elementary charges. In
Fig. 1.1 a general schematic of the polyelectrolyte structure is shown. The polyelectrolyte
ionizable groups, whose dissociation in solution makes the polyelectrolyte charged, leave
ions of one sign bound to the chain and mobile counterions in solution. The charged groups
contribute substantially to the chain stiffness and conformational degrees of freedom. The
properties of polyelectrolytes are similar to both: electrolytes (they exhibit electrolytic con-
ductivityandinterionicinteraction)andneutralpolymers(theirsolutionsareoftenviscous).
Polyelectrolytes are classified according to their origin as either natural or synthetic.
Many biological macromolecules are polyelectrolytes. The most important examples are
DNAandRNAmolecules,whichdissociateinsolutionformingastronglynegativelycharged
+ + +2polyion surrounded by an atmosphere of small mobile counterions, like K , Na , Ca and
+2Mg . Common synthetic polyelectrolytes are especially interesting for industrial applica-
tions because they dissolve in polar solvents like water, instead of most neutral hydrocarbon
polymers, which are only soluble in organic solvents [G¨ornitz1997]. Some natural polyelec-
trolytes, such as glue and gum, have been used from time immemorial as thickeners. The
use of gum as a protective colloid is as old as the use of India ink, which is finely ground10 CHAPTER 1. INTRODUCTION
soot, suspended in water and stabilized with gum arabic [Overbeek1976].
Despite their widespread presence and use, polyelectrolytes remain among the least un-
derstood materials in soft condensed matter. They are difficult to understand because of
the entwined correlations of chain configuration and polyelectrolyte charges. In analogy to
acids, one can distinguish weak and strong polyelectrolytes according to the degree of their
dissociation in solution. The strong polyelectrolytes completely dissociate in solution and
theirionicgroupsarepresentinalargepH–window(1 <pH<13)incontrasttoweakpolyelec-
trolytes that only partially dissociate at intermediate pH (6–8). Since weak polyelectrolytes
are not fully charged in solution their fractional charge can be modified by changing the
solution pH or ionic strength (measure of the ion concentration in solution).
Figure 1.1: Schematic of the polyelectrolyte macromolecule structure. Note that structure
may vary for different polyelectrolytes. Idea of the picture is adapted from A. Laschewsky
tutorial on polyelectrolytes.
1.2 Layer-by-Layer Assembly of Polyelectrolytes
In 1991, G. Decher and J.–D. Hong presented a new layer-by-layer (LbL) sequential
assembly technique for depositing ultrathin films [Decher1991]. This technique was first
suggested by R. K. Iler with regard to the concept of creating layers of oppositely charged
colloidalparticles[Iler1966]. Eachtimethataninitiallychargedsubstrateisexposedtoaso-
lution of oppositely charged polyions, a definite amount of polyelectrolyte (PE) is adsorbed.
Providedthateachadsorptionstepleadstochargeinversionofthesurface,thesubsequentde-
positionfinallyresultsinalayeredcomplex,stabilizedbystrongelectrostaticforces,so–called
self–assembled polyelectrolyte multilayer (PEM) [Sch¨onhoff2003a]. Schematic illustration of
the first two adsorption steps and resulting polyelectrolyte multilayer system, consisting of
several layers deposited onto planar solid support is shown in Figure 1.2. It is important
to note that with the exception of the conventional solution–dipping method developed by
Decher (a technique also used in this thesis) spraying and spin self–assembly methods were
introducedmorerecently[Schlenoff2000],[Cho2001]. Thesetechniquesprovidemuchshorter
processing times for multilayer build–up, which is important for PEMs, consisting of a large
number of layers; however, they have certain disadvantages. Thus, difference in film thick-