Nucleation in emulsion polymerization [Elektronische Ressource] : steps towards a non-micellar nucleation theory / von Pantea Nazaran

Pantea Nazaran

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• Publié par: universitat_potsdam
• Publié le: 01 janvier 2008
• Nombre de lectures: 9
• Langue: English
• Poids de l'ouvrage: 21 Mo

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Max Planck Institut für Kolloid und Grenzflächenforschung



Nucleation in Emulsion Polymerization
Steps towards a Non-micellar Nucleation Theory










Dissertation
zur Erlangung des akademischen Grades
"doctor rerum naturalium"
(Dr. rer. nat.)
in der Wissenschaftsdisziplin "Kolloidchemie"









eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam




von
Pantea Nazaran




Potsdam, Januar 2008
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Elektronisch veröffentlicht auf dem
Publikationsserver der Universität Potsdam:
http://opus.kobv.de/ubp/volltexte/2008/1752/
urn:nbn:de:kobv:517-opus-17521
[http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17521] Abstract
For more than 70 years, understanding of the mechanism of particle nucleation in
emulsion polymerization has been one of the most challenging issues in heterophase
polymerization research.
Within this work a comprehensive experimental study of particle nucleation in
emulsion polymerization of styrene at 70 °C and variety of conditions has been
performed. To follow the onset of nucleation, on-line conductivity measurements
were applied. This technique is highly sensitive to the mobility of conducting species
and hence, it can be employed to follow aggregation processes leading to particle
formation. On the other hand, by recording the optical transmission (turbidity) of the
reaction mixture particle growth was followed. Complementary to the on-line
investigations, off-line characterizations of the particle morphology and the molecular
weight have been performed. The aim was to achieve a better insight in the processes
taking place after starting the reaction via particle nucleation until formation of
colloidally stable latex particles.
With this experimental protocol the initial period of styrene emulsion polymerization
in the absence as well as in the presence of various surfactants (concentrations above
and below the critical micellization concentration) and also in the presence of seed
particles has been investigated. Ionic and non-ionic initiators (hydrophilic and
hydrophobic types) have been applied to start the polymerizations.
Following the above algorithm, experimental evidence has been obtained showing the
possibility of performing surfactant-free emulsion polymerization of styrene with oil-
soluble initiators. The duration of the pre-nucleation period (that is the time between
starting the polymerization and nucleation) can be precisely adjusted with the initiator
hydrophobicity, the equilibration time of styrene in water, and the surfactant
concentration. Spontaneous emulsification of monomer in water, as soon as both
phases are brought into contact, is a key factor to explain the experimental results.
The equilibration time of monomer in water as well as the type and concentration of
other materials in water (surfactants, seed particles, etc.) control the formation rate
and the size of the emulsified droplets and thus, have a strong influence on the
particle nucleation and the particle morphology.
2 Abstract
One of the main tasks was to investigate the effect of surfactant molecules and
especially micelles on the nucleation mechanism. Experimental results revealed that
in the presence of emulsifier micelles the conductivity pattern does not change
essentially. This means that the presence of emulsifiers does not change the
mechanism of particle formation qualitatively. However, surfactants assist in the
nucleation process as they lower the activation free energy of particle formation.
Contrary, seed particles influence particle nucleation, substantially. In the presence of
seed particles above a critical volume fraction the formation of new particles can be
suppressed. However, micelles and seed particles as absorbers exhibit a common
behavior under conditions where monomer equilibration is not allowed.
Results prove that the nucleation mechanism comprises the initiation of water soluble
oligomers in the aqueous phase followed by their aggregation. The process is
heterogeneous in nature due to the presence of monomer droplets.













3 Table of Contents

1 Introduction.................................................................................................6

1.1 History and general description........................................................................... 6

1.2 Basic issues; Nature of the problem..................................................................... 9

1.3 Scope and Objectives ..........................................................................................15

2 Experimental Section ................................................................................18

2.1 Materials..............................................................................................................18

2.2 On-line Investigations .........................................................................................20

2.2.1.1 On-line turbidity measurements.............................................................................22

2.2.1.2 On-line conductivity measurements.......................................................................24

2.2.1.3 On-line particle size measurements25

2.3 Off-line Investigations28

3 Results and Discussions.............................................................................30

3.1 Standard run: surfactant-free emulsion polymerization ...................................31

3.1.1 On-line conductivity measurement ........................................................................32

3.1.2 On-line turbidity measurement ..............................................................................35

3.1.3 Particle growth and morphology............................................................................37

3.2 On the role of initiator ........................................................................................45

3.3 Are surfactant micelles crucial for the nucleation? ...........................................63

3.4 More special cases ...............................................................................................79

3.4.1 Inisurfs .................................................................................................................79

3.4.2 Other monomers....................................................................................................81

4 Conclusion .................................................................................................89

5 Appendix93

5.1 Experimental details ...........................................................................................93

5.2 Additional information .......................................................................................96
4 Table of Contents

5.3 Categorized library of results ...........................................................................100

5.4 Symbols and Abbreviation................................................................................116

6 References................................................................................................120

5 Introduction
1 Introduction
1.1 History and general description
Polymers dominate our world. From naturally occurring polymers necessary to
sustain life, such as proteins, polynucleotides and polysaccharides, to man-made and
[1]commercialized macromolecules many important building blocks can be identified.
The observation of polymers and work devoted to their synthesis goes back to the
beginning of the 19th century. Since then, the growth of polymer science and industry
has been exorable. Major developments have been achieved in understanding and
control of different types of polymerization processes. Each year numerous papers,
patents and books appear dealing with various types and aspects of polymerization
[2]methods and polymer technology.
Heterophase polymerization techniques might be considered as the “working horse”
of industrial radical polymerization. Among the polymer synthesis methods, emulsion
polymerization has developed into a widely used process for the production of
synthetic latexes since its first introduction on an industrial scale during the early
20th century. Emulsion polymerization is a uniq