Theory and simulation of interfacial effects and phase behavior of nonionic surfactants [Elektronische Ressource] / von Simeon Stoyanov

Simeon Stoyanov

Sujets

• Physik
• Astronomie

Informations

• Publié par: universitat_duisburg-essen
• Publié le: 01 janvier 2002
• Nombre de lectures: 25
• Langue: English
• Poids de l'ouvrage: 6 Mo

Extrait

Theory and Simulation of Interfacial
Effects and Phase Behavior of
Nonionic Surfactants

Dissertation

zur Erlangung des Grades eines
Doktors der Naturwissenschaften
des Fachbereichs Chemie
der Universität Essen


von
Simeon Stoyanov
aus Sofia, Bulgaria



Essen 2002 Von Fachbereich Chemie (8) der Universität-GH Essen als Dissertation angenommen.
Referent: Prof. Dr. H. Rehage
Korreferent: F. Bandermann






Die vorliegende Dissertation wurde im Institut für Umweltanalytik und Angewandte
Geochemie des Fascbereichs Chemie (8) der Universität-GH Essen unter der Leitung von
Prof. Dr. H. Rehage angefertigt.








Many thanks to my scientific advisors and my colleagues from
University of Essen and from Henkel KGaA for all their support.


iiTo my daughter, Raya.















“ … a scientist must also be absolutely like a child. If he
sees a thing, he must say that he sees it, whether it was
what he thought he was going to see or not. See first,
think later, then test. But always see first. Otherwise
you will only see what you were expecting. Most
scientist forget that. I’ll show you something to
demonstrate that latter …”
Wonko the Sane in “So long and thanks for all the fish”
Douglas Adams
iiiCONTENTS

I. Introduction and motivation of the thesis ..........................................................................1
I.1. Surfactants .......................................................................................................................1
I.2. Surfactants phase behavior ..............................................................................................1
I.3. Surfactant interfacial properties.......................................................................................3
I.4. Static and dynamic properties - “effective” concentration concept.................................8
I.5. Self Consistent Field Theory of Polymers - Is it anything to do with surfactants?.......11
I.6. Aim of the thesis............................................................................................................17
I.7. Outline of the thesis .......................................................................................................18

II. Introduction to Self Consistent Field Theory of Polymer Brushes ..............................20
II.1. Polymer Brushes at flat interface .................................................................................20
II.2. Brush at Curved interface.............................................................................................27

III. Bending constants of interfaces containing surfactants or polymers .........................31
III.1. Introduction and Motivation .......................................................................................31
III.2. Bending constants for the case of constant area per molecule....................................33
III.2. Variation of the surface area with respect of the curvature ........................................41
III.3. Same simple applications - Grafted polymer brushes.................................................49
III.3.1 Very low volume fractions case............................................................................50
χ =1/ 2ΘIII.3.2. solvent ( ) and low volume fractions ..................................................52
III.3.3. Intermediate case of small volume fractions (cubic DFT)...................................53
χ = 0III.3.4. Case for , arbitrary volume fractions..........................................................57
III.3.5. Some remarks on the general case .......................................................................59
III.4. Conclusions and perspectives .....................................................................................60

IV. Dissipative Particle Dynamics - method and its applications for studying properties
of colloidal systems.................................................................................................................62
IV.1. Introduction.................................................................................................................62
ivIV.2. DPD Basics .................................................................................................................63
IV.3. Some applications of DPD for modeling of colloidal systems...................................75
IV.3.1. Modeling phase behavior of ethoxylated surfactants in dynamic and static
conditions. ........................................................................................................................79
IV.3.2. Modeling surface tension of surfactant systems..................................................83
IV.3.3. Systems containing surfactants and long polymers .............................................84
IV.3.4. Modeling of wetting phenomena- spreading of oil drops on a solid substrate....88
IV.3.5. Modeling droplet detachment from a solid wall in shear flow............................89
IV.4. Conclusions.................................................................................................................93

V. Polymers at Interfaces - Comparison Between Self Consistent Field Theory and
Dissipative Particle Dynamics Computer Simulations.......................................................94
V.1. Introduction....94
V.2. Theoretical Background ...............................................................................................96
V.3. Simulation Details......................................................................................................102
V.4. Results and Discussions .............................................................................................107
V.5. Summary ....................................................................................................................116

VI. Self-Consistent Field Interfacial Tension Isotherm of surfactants: Comparison with
experimental data.................................................................................................................117
VI.1. Introduction...............................................................................................................117
VI.1.1. Surface tension of pure interfaces......................................................................117
VI.1.2. Surface tension of interfaces containing surfactants..........................................119
VI.2. SCF Surface Tension Isotherm for a nonionic surfactant.........................................123
VI.3. Practical application of the SCF adsorption isotherm ..............................................126
VI.4. Comparison of the SCF theory predictions with experimental data.........................129
VI.4.1. Surface and interfacial tension of non-ionic surfactants....................................129
VI.4.2. Comparison between SCF theory, experimental isotherm and DPD simulation of
interfacial (water/hexane) tension of amphoteric surfactant DDAO .............................138
VI.4.3. Surface and interfacial tension of ionic surfactants ...........................................143
VI.5 Conclusions................................................................................................................151
vVII.1. General Conclusions .................................................................................................152
VII.2. Zusammenfassung.....................................................................................................155

List of References .................................................................................................................158

Curriculum Vitae164



vi I. Introduction and motivation of the thesis
I. Introduction and motivation of the thesis
I.1. Surfactants
1-7Surfactants are one of the main components in various colloidal systems . They
consist of two parts – hydrophilic and hydrophobic and their properties are result of the
“fight” between them. The hydrophobic part is usually a long (CH ) chain, which is called 2 k
tail, while the hydrophilic part usually is much shorter and is called head of surfactant. The
hydrophobic chain could be also branched or contain different organic segments.
8-9Depending their electric properties , surfactants could be nonionic (whole molecule
is uncharged) and ionic (part of molecule is charged or it has distributed charges along it –
which is called poly-electrolyte) or zwitter-ionic, where surfactant molecule is uncharged but
has high dipolar moment. The charge of the surfactant molecule could change with the
condition change like pH and ionic strength of solution, temperature, aggregation of
surfactant molecule with other substances etc. Depending on the conditions one and the same
8molecule could be uncharged or charged or even can invert its charge .
The main subject of this study are nonionic surfactants, but later on, in the last part of
the thesis we will show that some of the results, which are obtained for nonionics could also