Transport mechanisms and wetting dynamics in molecularly thin films of long-chain alkanes at solid,vapour interface [Elektronische Ressource] : relation to the solid-liquid phase transition / von Paul Lažar
143 pages
English

Transport mechanisms and wetting dynamics in molecularly thin films of long-chain alkanes at solid,vapour interface [Elektronische Ressource] : relation to the solid-liquid phase transition / von Paul Lažar

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143 pages
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Aus dem Max Planck Institut urf¨ Kolloid und Grenzflachenforschung¨Abteilung Grenzflachen,¨ Arbeitsgruppe: PD Dr. Hans RieglerundInternational Max Planck Research School on Biomimetic SystemsTransport mechanisms and wetting dynamics inmolecularly thin films of long chain alkanes at solid/vapourinterface: relation to the solid liquid phase transitionDissertationzur Erlangung des akademischen GradesDoktor der Naturwissenschaften”doctor rerum naturalium”(Dr. rer. nat.)in der Wissenschaftsdisziplin Experimentalphysikeingereicht an der¨Mathematisch Naturwissenschaftlichen Fakultatder Universitat¨ PotsdamvonPaul Lazar˘geboren am 17.09.1972 in Focs ¸ani Vrancea, Rumanien¨Potsdam, Februar 2005To my sisters, Veronica and GabrielaSurorilor mele, Veronica s¸i GabrielaContents1. Introduction 52. Theoretical background 72.1. Interfacial thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.1.1. Interfacial and surface energies . . . . . . . . . . . . . . . . . . . . . . . . . 72.1.2. Statics of wetting, Young equation . . . . . . . . . . . . . . . . . . . . . . . 72.1.3. Work of adhesion and cohesion . . . . . . . . . . . . . . . . . . . . . . . . 92.1.4. Laplace equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.1.5. Molecular and surface forces . . . . . . . . . . . . . . . . . . . . . . . . . . 102.1.6. Thin films and disjoining pressure . . . . . . . . . . . . . . . . . . . . . . . 122.2.

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Publié le 01 janvier 2005
Nombre de lectures 9
Langue English
Poids de l'ouvrage 10 Mo

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Aus dem Max Planck Institut urf¨ Kolloid und Grenzflachenforschung¨
Abteilung Grenzflachen,¨ Arbeitsgruppe: PD Dr. Hans Riegler
und
International Max Planck Research School on Biomimetic Systems
Transport mechanisms and wetting dynamics in
molecularly thin films of long chain alkanes at solid/vapour
interface: relation to the solid liquid phase transition
Dissertation
zur Erlangung des akademischen Grades
Doktor der Naturwissenschaften
”doctor rerum naturalium”
(Dr. rer. nat.)
in der Wissenschaftsdisziplin Experimentalphysik
eingereicht an der
¨Mathematisch Naturwissenschaftlichen Fakultat
der Universitat¨ Potsdam
von
Paul Lazar˘
geboren am 17.09.1972 in Focs ¸ani Vrancea, Rumanien¨
Potsdam, Februar 2005To my sisters, Veronica and Gabriela
Surorilor mele, Veronica s¸i GabrielaContents
1. Introduction 5
2. Theoretical background 7
2.1. Interfacial thermodynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.1. Interfacial and surface energies . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.2. Statics of wetting, Young equation . . . . . . . . . . . . . . . . . . . . . . . 7
2.1.3. Work of adhesion and cohesion . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.4. Laplace equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.1.5. Molecular and surface forces . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.1.6. Thin films and disjoining pressure . . . . . . . . . . . . . . . . . . . . . . . 12
2.2. Wetting dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.1. Models describing the wetting dynamics . . . . . . . . . . . . . . . . . . . . 15
2.2.2. The hydrodynamic model . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2.3. The molecular kinetic model . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.2.4. Precursor films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3. Running Droplets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.3.1. Passive drops on a chemically heterogeneous solid surface . . . . . . . . . . 22
2.3.2. Reactive wetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.3.3. Velocity of running drops . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
2.4. Physico chemical properties of n alkanes . . . . . . . . . . . . . . . . . . . . . . . 26
2.4.1. Bulk, crystalline n alkane structures at low temperatures . . . . . . . . . . . 27
2.4.2. Bulk structural behaviour in the vicinity of the melting point . . . . . . . . . 27
2.4.3. Interfacial behaviour, surface freezing . . . . . . . . . . . . . . . . . . . . . 28
2.5. Theory of melting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
2.5.1. Bulk melting mechanisms, surface premelting . . . . . . . . . . . . . . . . . 30
2.5.2. Influence of size, dimensionality and confinement on the melting temperature 31
2.6. Classical nucleation theory, crystallization from melt . . . . . . . . . . . . . . . . . 33
2.6.1. Homogeneous nucleation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
2.6.2. Heterogeneous . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3. Experimental methods and equipment 39
3.1. Specular X ray reflectometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1.1. Basic concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1.2. Kiessig fringes and Bragg peaks . . . . . . . . . . . . . . . . . . . . . . . . 40
3.2. Atomic force microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.3. Optical microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1Contents
4. Materials and sample preparation 47
4.0.1. Alkanes and substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5. Droplet solidification by growing molecularly thin terraces 49
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.2. Nucleation of bulk solidification and terrace growth . . . . . . . . . . . . . . . . . . 51
5.3. Structure and thickness of the growing film . . . . . . . . . . . . . . . . . . . . . . 54
5.3.1. Optical microscopy and AFM . . . . . . . . . . . . . . . . . . . . . . . . . 54
5.3.2. Small angle X ray reflectivity data . . . . . . . . . . . . . . . . . . . . . . . 54
5.4. Equations describing the kinetics of terrace growth . . . . . . . . . . . . . . . . . . 58
5.5. Kinetics of sequential growth of monomolecular terraces at constant temperature . . 60
5.5.1. Growth of the second terrace on top of the first one . . . . . . . . . . . . . . 60
5.5.2. Kinetics of growth for first, second, and third monomolecular layer . . . . . 62
5.6. Influence of temperature on the terrace growth kinetics . . . . . . . . . . . . . . . . 63
5.7. Behaviour of the solidified ”drops” . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
5.8. Monolayer growth from a solid on the bare silicon substrate . . . . . . . . . . . . . . 65
5.9. Terrace behaviour above bulk melting point . . . . . . . . . . . . . . . . . . . . . . 68
5.10. Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
6. Reversible running drops driven by the S-L phase transition 73
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
6.2. Nucleation of the advancing running droplets . . . . . . . . . . . . . . . . . . . . . 73
6.2.1. Instability of the wetting stripe at the terrace edge . . . . . . . . . . . . . . . 75
6.2.2. Critical radius and free energy barrier . . . . . . . . . . . . . . . . . . . . . 76
6.3. Kinetics of running droplets on melting . . . . . . . . . . . . . . . . . . . . . . . . 77
6.3.1. Dynamic contact angle of running droplets . . . . . . . . . . . . . . . . . . 80
6.3.2. Dependence of velocity on droplet size . . . . . . . . . . . . . . . . . . . . 82
6.3.3. of v on temperature and number of molecular layers . . . 83
6.3.4. Generalized dependence of velocity versus terrace thickness and overheating 86
6.3.5. Driving force: Surface tension or melting free energy? . . . . . . . . . . . . 87
6.3.6. Calculation of the temperature slope of the driving force using the hydrody
namic model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.3.7. Dewetting Kinetics of the all liquid film . . . . . . . . . . . . . . . . . . . . 91
6.4. Running droplets driven by solidification . . . . . . . . . . . . . . . . . . . . . . . . 93
6.4.1. Temperature dependence of the velocity for solidification driven running drops 93
6.4.2. Sequential initiation of solidifying running droplets . . . . . . . . . . . . . . 95
6.4.3. Mechanism of solidification driven drops when thin solid terraces are
formed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
6.5. Discussion and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
7. Overheating aspects of solid alkane films of different thickness 101
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
7.2. Thermodynamic considerations for melting of a monolayer thick solid terrace . . . . 102
MN7.2.1. The (absolute) thermodynamic limit of overheating, T . . . . . . . . . . . 106
7.2.2. Hierarchy of the melting mechanisms . . . . . . . . . . . . . . . . . . . . . 106
2Contents
7.3. Overheating of thick terraces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
7.4. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
8. Conclusions 115
Bibliography 117
A. Appendix iii
A.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
A.1.1. Useful relations between different parameters describing spherical cap shaped
drops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
A.2. Fresnel reflectivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
A.3. Home made equipment, special set up . . . . . . . . . . . . . . . . . . . . . . . . . viii
A.4. Mechanism dependent equations describing the growth kinetics of a thin solid film . x
A.4.1. Release limited, constant mass flux per unit length of contact line . . . . . . x
A.4.2. Growth limited, rate of solidification at the edge . . . . . . . . . . . xi
A.4.3. Transport limited, ”diffusion like” transport . . . . . . . . . . . . . . . . . . xi
A.5. Free energy gain upon spontaneous dewetting . . . . . . . . . . . . . . . . . . . . . xiv
A.6. Instability of a droplet wetting the step region . . . . . . . . . . . . . . . . . . . . . xvi
B. Acknowledgments xix
31. Introduction
Surfaces and interfaces can be found everywhere around us. In the last decades, surface science and
technology is subject of increasing interest due to the general trend of miniaturization. Many modern
applications require a good control of the way small amounts of liquid are transported. Liquids in
micro or nanochannels must be pumped, distributed, mixed or forced to flow in jets (printing) in a
controlled way. For the scale at which these processes occur, the classical methods of handling liquids
(e.g. mechanical pumps or electrical valves) are either ineffective or it is technologically difficult to

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