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Published on: February 17, 2019
Binary fluid with attractions near a planar wall.
Venkat Padmanabhan1, Amalie L Frischknecht, Michael E Mackay
1Department of Materials Science and Engineering, University of Delaware, Newark, 19716, USA.
Small particles can displace larger ones from surfaces when they are attracted to the wall. This finding, confirmed by simulations and theory, is robust across various conditions.
Area of Science:
- Physics
- Physical Chemistry
- Materials Science
Background:
- Mixtures of large and small hard spheres typically segregate at planar walls due to entropy.
- Larger spheres preferentially adsorb to substrates to minimize system entropy loss per unit area.
Purpose of the Study:
- To investigate the role of attractive forces between small particles and a wall in altering segregation patterns.
- To determine if small particles can displace larger particles from a surface layer.
Main Methods:
- Utilized fluids density-functional theory (DFT).
- Employed discontinuous molecular dynamics (DMD) simulations.
- Explored parameters including relative sphere size, concentration, and inter-particle attractions.
Main Results:
- An attractive potential between small particles and the wall, on the order of thermal energy, can dislodge larger particles.
- Small particles become the dominant component at the surface layer under specific attractive conditions.
- The observed phenomenon is robust across a range of tested parameters.
Conclusions:
- Attractive interactions between small particles and surfaces can overcome entropic segregation effects.
- This mechanism offers a route to control particle distribution at interfaces.
- The findings have implications for understanding and engineering interfacial phenomena in colloidal systems.

