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Thermophoresis in Colloidal Suspensions
This dissertation examines the motion of colloids in a temperature gradient, a non-equilibrium
phenomenon also known as thermophoresis. Chapter 1 gives an introduction to the existing
applications and basic concepts of thermophoresis and outlines some of the experimental and
theoretical challenges that serve as a motivation for this PhD project. In Chapter 2, a general
theoretical description for thermophoresis is formulated using the theory of non-equilibrium
thermodynamics. The colloidal flux is split up into an interfacial single-colloid contribution
and a bulk contribution, followed by a determination of transport coefficients based on
Onsager’s reciprocal relations. It is further shown how the phenomenological expression
of the thermophoretic flux can be recovered when the fluid is at steady-state. The results
issuing from this description are then discussed and compared to other existing approaches,
some of which are shown to neglect the hydrodynamic character of colloidal thermophoresis.
Chapter 3 is dedicated to the validation of the introduced theoretical framework by means
of computer simulations, using a simulation technique known as multi-particle collision
dynamics. More specifically, the dependence of the thermophoretic force on different system
parameters is examined and deviations from the theoretical prediction are explained by an
advective distortion of interfacial fluid properties at the colloidal surface. Chapter 4 presents
steady-state measurements of functionalised colloids in a temperature gradient, showing
how the addition of molecular surface groups increases the experimental complexity of
thermophoretic motion. The relaxation process behind this steady-state is also studied, to
determine how the relaxation speed depends on the applied temperature gradient. In chapter
5, a general conclusion is drawn from the presented work and its implications are briefly
discussed in relation to the current state of knowledge. Finally, the discussion is closed with
an outlook on remaining challenges in understanding colloidal motion that could be the
subject of future research
Datafile 2 for Cael Bisson Follows 2017 Limnology & Oceanography Letters
NCEP ESRL COBE SST reanalysis as retrieved 2 August 2016; see associated metadata file for full descriptio