Modeling of complex chemical reactions and macromolecular orientation phenomena in confined geometries [Elektronische Ressource] / vorgelegt von Rodrigo Maghdissian Cordeiro

Cordeiro

Informations

• Publié par: johannes_gutenberg-universitat_mainz
• Publié le: 01 janvier 2007
• Nombre de lectures: 11
• Langue: English
• Poids de l'ouvrage: 22 Mo

Extrait

Modeling of Complex Chemical Reactions and
Macromolecular Orientation Phenomena
in Confined Geometries



Dissertation zur Erlangung des Grades
“Doktor der Naturwissenschaften”


am Fachbereich Chemie
der Johannes Gutenberg-Universität
in Mainz


vorgelegt von
Rodrigo Maghdissian Cordeiro
geboren in Brasilien



Mainz, 2007






Tag der mündlichen Prüfung: 22.05.2007


























Die vorliegende Arbeit wurde im Zeitraum Oktober 2003 bis April 2007 am Max-
Planck-Institut für Polymerforschung in Mainz angefertigt.
Contents

1 Introduction ……………………………………………………………. 1
1.1 Motivation ……………………………………………………………. 1
1.2 Tasks and Strategies ………………………………………………….. 3
1.3 Organization …………………………………………………………… 4
1.3.1 Basic Organization of the Present Work ……………………….. 4
1.3.2 Simulation Methods (Chapter 2) ……………………………….. 4
1.3.3 Implementing Geometrical Confinement in Simulations
(Chapter 3) …………………………………………………….. 5
1.3.4 Polymerization in Nanoreactors (Chapter 4) …………………. 5
1.3.5 Polymer Chain Orientation in Confined Geometries
(Chapter 5) ……………………………………………………. 6
1.3.6 Patterning of Polymer Film Surfaces by Droplet Deposition
(Chapter 6) ……………………………………………………. 7
1.3.7 Oscillating Chemical Reactions in Confined Geometries
(Chapter 7) ……………………………………………………. 7

2 Simulation Method ………………………………………………….... 9
2.1 The Monte Carlo Method ……………………………………………. 9
2.1.1 Historical and Fundamental Aspects …………………………. 9
2.1.2 Statistical Thermodynamics – The Canonical Ensemble …….. 10
2.1.3 Importance Sampling …………………………………………. 12
2.1.4 Ergodicity ……………………………………………………... 14
2.1.5 Inhomogeneous Systems ……………………………………… 15
2.1.6 Dynamic Properties …………………………………………… 16
2.1.7 System Boundaries and Finite Size Effects …………………... 18
2.1.8 Errors and Limitations ………………………………………... 19
2.2 Simulation of Polymer Chains ……………………………………….. 20
2.2.1 Fundamental Aspects of Polymer Physics ……………………. 20
2.2.2 Monte Carlo Simulations of Polymer Chains on a Lattice …… 24 2.3 The Cooperative Motion Algorithm …………………………………. 27

3 Implementing Geometrical Confinement in Simulations …… 32
3.1 Confined Systems ……………………………………………………. 32
3.2 Simulation of Small Liquid Droplets at Surfaces ……………………... 33

4 Polymerization in Nanoreactors …………………………………... 46
4.1 Introduction to the Modeling of Equilibrium Step-Growth
Polymerization in Confined Geometries ………………………………. 46
4.2 Methodology …………………………………………………………... 47
4.3 Implementation Details ………………………………………………... 48
4.4 Simulation Results and Analytical Theory for Lamellae, Tubes and
Droplets ………………………………………………………………... 50
4.5 Final Considerations ….……………………………………………….. 60

5 Polymer Chain Orientation in Confined Geometries ………… 62
5.1 Scientific Background ………………………………………………... 62
5.2 Methodology …………………………………………………………. 63
5.3 Simulation of Orientation of Polymer Chains Confined Between Rigid
Walls …………………………………………………………………. 64
5.3.1 Implementation Details ……………………………………….. 64
5.3.2 Simulation Results ……………………………………………. 68
5.3.3 Analytical Model ……………………………………………… 73
5.4 Comparison with Experimental Data from the Literature ……………. 78
5.5 Own Experiments with Conjugated Polymers ……………………….. 83
5.5.1 Materials and Experimental Methods ………………………… 83
5.5.2 Experimental Results …………………………………………. 84
5.6 Limitations of the Model and Final Considerations …………………. 87

6 Patterning of Polymer Film Surfaces by Droplet Deposition . 90
6.1 Experimental Background ……………………………………………. 90
6.2 Methodology …………………………………………………………. 91
6.3 Molecular Modeling of Evaporating Droplets at Soluble Surfaces ….. 93 6.3.1 Generation of Droplets at Surfaces and Simulation of
Evaporation …………………………………………………… 93
6.3.2 General Case of Pattern Formation …………………………… 95
6.3.3 Explicit Consideration of Polymer Chains and Influence of
Chain Orientation ……………………………………………... 100
6.4 Final Considerations …………………………………………………. 102

105 7 Oscillating Chemical Reactions in Confined Geometries ……
105 7.1 Scientific Background ………………………………………………...
107 7.2 Methodology ………………………………………………………….
108 7.3 Model Implementation ………………………………………………..
114 7.4 Simulation Results and Discussion …………………………………...
124 7.5 Final Considerations ………………………………………………….

126 8 Summary ………………………………………………………………...

References ………………………………………………………………. 128

Acknowledgements …………………………………………………… 136

List of Publications 137

Curriculum Vitae ……………………………………………………... 138



1

Introduction



1.1 Motivation

Nature is full of examples of molecular processes taking place under spatial
restrictions. To begin with, the cell is essentially a confined environment [Minton’92].
In this sense, spatial restrictions may be a key factor cleverly explored by the cell
machinery. From the technological point of view, there has been an increasing interest
in chemical and physical processes taking place under confinement. Several catalysers
used in industry are essentially nanoporous materials, as is the case of zeolites. In
such materials, there is a huge area of contact between the catalyst surface and the
reactants. This contributes to the increased rate of reactant conversion. In addition to
that, the sterical hindrance imposed by the small pores may also have an impact on
chemical processes. Very large molecules or those which do not have chemical
affinity with the porous material are less likely to penetrate into the porous structure
and be converted to products. Analogously, the generation of molecules which do not
fit into the pore structure is expected to be hindered. Of course, zeolites constitute
only a particular example of confined environment. Lipid vesicles, emulsions, small
droplets and thin films may all be considered as confined systems. Furthermore, since
its advent, the field of nanotechnology has enabled the development of new materials
and engineering of new devices, and thanks to that there is today a myriad of
materials whose nanoscopic structure could be explored for instance as nanoreactors.
Carbon nanotubes are just one example. 2
Although the engineering and production of the materials cited above is
already quite advanced, several basic aspects related to the chemistry and physics
under space restrictions still need to be understood. The issue is complex since there
are several ways according to which confinement may completely change the
dynamics of a system or its equilibrium state. First, there are finite size effects
associated with confinement, so that the correlation length associated with some
processes may be comparable to the size of the nanoscopic system. Second, there are
boundary effects in the sense that, due to space restrictions, molecules can react with a
finite number of neighbors in their proximity [Provata’93]. Not to mention that
physical processes like diffusion and molecular orientation may be strongly
influenced by confinement as well.
There were mainly two practical questions which motivated this work and
were the starting point of all other additional investigations performed here. It is
known experimentally that, in thin polymer films, polymer chain segments are
preferably oriented parallel to the surface of the film [Prest’79, Prest’80, Russel’83,
Boese’92, Lin’93, Lin’94, Ree’94, Coburn’94, Li’97, Li’99, Lee’03, McBranch’95,
Tammer’02, Koynov’04, Koynov’06]. There is a great interest in this topic because
polymer films are commonly used for technological applications. It is for instance
known that, in organic light emitting diodes (OLEDs), the intensity of light emitted
perpendicular to the film surface depends intrinsically on the chain orientation within
the film [Friend’99]. There is still a considerable need for modeling and simulation to
get an improved basic understanding of the orientation phenomena and the influence
of parameters such as film thickness, molecular weight and chain r