Thermal diffusion in liquid mixtures and polymer solutions by molecular dynamics simulations [Elektronische Ressource] / vorgelegt von Meimei Zhang

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Informations

• Publié par: technischen_universitat_darmstadt
• Publié le: 01 janvier 2007
• Nombre de lectures: 20
• Langue: English

Extrait

Thermal Diffusion in Liquid Mixtures and
Polymer Solutions by Molecular Dynamics
Simulations
Vom Fachbereich Chemie
der Technischen Universität Darmstadt
zur Erlangung des akademischen Grades eines
Doctor rerum naturalium (Dr. rer. nat.)
genehmigte
Dissertation
vorgelegt von
Dipl.-Ing. Meimei Zhang
aus Zhe Jiang, China
Berichterstatter: Professor Dr. Florian Müller-Plathe
Mitberichterstatter: Professor Dr. Rolf Schäfer
Tag der Einreichung: 12. 12. 2006
Tag der mündlichen Prüfung: 05. 02. 2007
Darmstadt 2006
D17ACKNOWLEDGMENTS
I would like to thank my thesis advisor, Professor Dr. Florian
Müller-Plathe for his support, his guidance and his patience to make this
thesis possible.
I would also like to thank my colleagues, Dr. Sudip Roy, Dr.
Hossein Eslami, and Dr. Volker Weiss, for the English correction of the
thesis. Thanks to Dr. Bernd Schilling for the format help.
Special thanks to my colleague Mr. Thomas Müller and our secretary
Ms. Gabriele General for the German language help.
I also want to thank Professor Dr. Giuseppe Milano at the University
of Salerno for helpful discussion in my research.
Thanks to Professor Dr. Rolf Schäfer and the other defense
committee members for showing interests to this thesis.
Thanks to all the members in the research group for giving me
friendship and happiness.
Finally, I would thank my family for their endless support. Contents
List of Figures..........................................................................................................III
List of Tables ...........................................................................................................VI
Zusammenfassung ................................................................................................. VII
Abstract ...................................................................................................................IX
1 Introduction ...........................................................................................................1
1.1 Definition and significance of the research in thermal diffusion ......................1
1.2 Historical background of thermal diffusion research .......................................2
1.2.1 Theoretical studies................................................................................2
1.2.2 Experimental studies.............................................................................3
1.2.3 Simulation studies5
1.3 Aim and layout of the thesis............................................................................6
2 Theory of heat conduction and matter transport in binary liquids..........................10
2.1 Definition of transport coefficients in Onsager reciprocal relations ...............10
2.2 Molecular dynamics calculation of transport coefficients ..............................13
2.2.1 Equilibrium molecular dynamics (EMD) ............................................13
2.2.2 Synthetic non-equilibrium molecular dynamics (S-NEMD) ................16
2.2.3 Direct (boundary driven) non-equilibrium molecular dynamics...........17
3 Thermal conductivities in benzene-cyclohexane systems......................................23
3.1 Introduction ..................................................................................................23
3.2 Computational details ...................................................................................24
3.3 Result and discussion....................................................................................27
3.3.1 Benzene..............................................................................................27
3.3.2 Cyclohexane.......................................................................................31
3.3.3 Mixtures of benzene and cyclohexane.................................................34
3.3.4 Equipartition of the kinetic energy ......................................................35
3.4 Conclusions37
4 Thermal diffusion in liquid benzene-cyclohexane mixtures ..................................40
4.1 Introduction40
4.2 Computational details ...................................................................................41
4.3 Result and discussion....................................................................................42
4.3.1 Preliminary study: Establishing the steady state..................................42
I4.3.2 Preliminary study: Sensitivity of the Soret effect to simulation
parameters.......................................................................................... 45
4.3.3 Concentration dependence of the Soret coefficient ............................. 48
4.3.4 Temperature dependence of the Soret coefficient................................ 51
4.4 Conclusions.................................................................................................. 51
5 Thermal diffusion in dilute polymer solutions: Influence of chain length,
chain stiffness, and solvent quality ...................................................................... 54
5.1 Introduction 54
5.2 Computational details................................................................................... 56
5.3 Result and discussion 57
5.3.1 Influence of solvent quality ................................................................ 57
5.3.2 Influence of chain length and chain stiffness....................................... 59
5.3.3 Influence of the monomer mole fraction............................................. 62
5.4 Conclusions.................................................................................................. 63
6 Summary............................................................................................................. 66
Simulation Tools...................................................................................................... 69
Publication Lists...................................................................................................... 70
IIList of Figures
2.1 Schematic representation of periodic boundary conditions in two
dimensions......................................................................................................18
3.1 Temperature profiles in the RNEMD simulation of benzene for three
perturbations (W = 150, 300, 500). The two symmetric sides of the
simulation cells have been averaged. Linear least-squares fits to the
data points are shown, too. ..............................................................................28
3.2 Density profiles in the RNEMD simulation of benzene for three
perturbations (W = 150, 300, 500). The two symmetric sides of the
simulation cells have been averaged. Linear least-squares fits to the
data points are shown, too.28
3.3 Cumulative average of the thermal conductivity of benzene at the
smallest perturbation (W = 500). It shows the slowest convergence of
all simulations in this contribution...................................................................29
3.4 Cumulative average of the thermal conductivity of benzene at the
intermediate perturbation (W = 300)................................................................29
3.5 Cumulative average of the thermal conductivity of benzene at the
strongest perturbation (W = 150). ....................................................................30
3.6 Temperature profiles in the RNEMD simulation of cyclohexane for
three perturbations. The two symmetric sides of the simulation cells
have been averaged. Linear least-squares fits to the data points are
shown, too.......................................................................................................32
3.7 Density profiles in the RNEMD simulation of cyclohexane for three
perturbations. The two symmetric sides of the simulation cells have
been averaged. Linear least-squares fits to the data points are shown,
too...................................................................................................................32
3.8 Cumulative average of the thermal conductivity of cyclohexane at the
strongest perturbation (W = 150). ....................................................................33
3.9 Cumulative average of the thermal conductivity of cyclohexane at the
intermediate perturbation (W = 300)................................................................33
3.10 Cumulative average of the thermal conductivity of cyclohexane at the
smallest perturbation (W = 500).......................................................................34
III3.11 Calculated thermal conductivities of benzene-cyclohexane mixtures at
around 300 K, W = 150 (pure fluids) and W = 100 (mixtures). ........................ 35
3.12 Temperature profiles for the different degrees of freedom for benzene
at the weakest perturbation (W = 500, no thermostat, 308 K). The two
symmetric sides of the simulation cells have been averaged............................ 36
3.13 Temperature profiles for the different degrees of freedom for benzene
at the strongest perturbation (W = 150, no thermostat, 308 K). The two
symmetric sides of the simulation cells have been averaged............................ 36
3.14 Temperature profiles for t