Thermophoresis beyond Local Thermodynamic Equilibrium

Area of Science:

• Colloid science
• Soft matter physics
• Transport phenomena

Background:

• Thermophoresis describes particle movement in response to temperature gradients.
• Understanding nonlinear thermophoresis is crucial for applications like particle separation and thermal management.
• Existing linear models fail to capture complex behaviors at higher temperature gradients.

Purpose of the Study:

• To investigate the thermophoretic behavior of polystyrene beads across a broad range of temperature gradients.
• To identify and characterize the transition to nonlinear thermophoresis.
• To compare experimental findings with existing theoretical models.

Main Methods:

• Experimental measurement of polystyrene bead thermophoresis.
• Systematic variation of temperature gradients, particle sizes, and salt concentrations.
• Data analysis using Péclet number and master curve rescaling.

Main Results:

• Observed pronounced nonlinear thermophoretic characteristics.
• Identified a transition to nonlinear behavior marked by slowed motion at a Péclet number of order unity.
• Demonstrated data collapse onto a single master curve for the nonlinear regime.
• Found agreement with linear models at low gradients but discrepancies at higher gradients.

Conclusions:

• Thermophoresis transitions from fluctuation-dominated at low gradients to drift-dominated at higher Péclet numbers.
• This behavior contrasts sharply with electrophoresis.
• The findings highlight the importance of fluctuations and nonlinear effects in thermophoresis.