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Short range attraction between two similarly charged silica surfaces
Ohad Zohar1, Ilya Leizerson, Uri Sivan
1Faculty of Physics and the Russell Berrie Nanotechnology Institute, Technion - Israel Institute of Technology, Haifa.
Physical Review Letters
|May 23, 2006
Summary
The addition of cobalt hexamine ions to saline solutions suppresses repulsion between charged silica surfaces, inducing attraction at short distances. This attraction reverses to repulsion at higher ion concentrations.
Area of Science:
- Colloid and Surface Science
- Physical Chemistry
- Materials Science
Background:
- Understanding interparticle forces is crucial for controlling colloidal systems.
- Silica surfaces in saline solutions typically exhibit repulsive electrostatic interactions.
- The influence of multivalent ions on surface forces requires further investigation.
Purpose of the Study:
- To investigate the effect of cobalt hexamine ions on the interaction forces between charged silica surfaces.
- To determine the conditions under which attraction and repulsion dominate.
- To quantify the surface density and association constants of cobalt hexamine ions.
Main Methods:
- Utilizing atomic force microscopy to measure forces between silica surfaces.
- Systematically varying the concentration of cobalt hexamine ions in a saline solution.
- Analyzing surface charge renormalization to estimate ion adsorption.
Main Results:
- Pure NaCl solutions resulted in repulsive forces between silica surfaces.
- Cobalt hexamine ions (Co(NH(3))(6)(+3)) induced attraction at short distances, suppressing repulsion.
- Increased cobalt hexamine concentrations led to a reversal from attraction back to repulsion.
- Surface charge renormalization measurements provided estimates for ion surface density and association constants.
Conclusions:
- Cobalt hexamine ions significantly alter the interaction forces between charged silica surfaces.
- The observed attraction is concentration-dependent and occurs at distances shorter than the electrostatic screening length.
- The findings provide insights into the role of multivalent ions in colloidal interactions and suggest alternative mechanisms beyond Wigner crystal interactions.