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Measurement of dynamical forces between deformable drops using the atomic force microscope. I. Theory.
Steven L Carnie1, Derek Y C Chan, Craig Lewis
1Department of Mathematics and Statistics, Particulate Fluids Processing Centre, University of Melbourne, Parkville 3010, Australia. s.carnie@ms.unimelb.edu.au
Langmuir : the ACS Journal of Surfaces and Colloids
|March 23, 2005
Summary
Researchers measured forces between moving liquid drops using atomic force microscopy (AFM). A theoretical model explained experimental results, showing drop flattening and attractive forces from hydrodynamics.
Area of Science:
- Fluid dynamics
- Surface science
- Microscopy
Background:
- Experimental measurements of dynamical forces between moving liquid drops in solution are now possible.
- The experimental regime involves significant surface forces, hydrodynamics, and drop deformation.
- Existing models may not fully capture the interplay of these factors.
Purpose of the Study:
- To develop a theoretical model for dynamical forces between two moving liquid drops in solution.
- To explain experimental observations from atomic force microscopy (AFM) measurements.
- To understand the contributions of surface forces, hydrodynamics, and drop deformation to the measured forces.
Main Methods:
- Developed a detailed theoretical model of the experimental setup.
- Incorporated surface forces, hydrodynamic interactions, droplet deformation, and AFM cantilever deflection into the model.
- Compared model predictions with experimental force curves.
Main Results:
- The theoretical model accurately reproduced experimental force curves.
- Observed pseudo-constant compliance regions in force curves, attributed to drop flattening.
- Identified attractive pull-off forces, primarily caused by hydrodynamic lubrication forces.
Conclusions:
- The developed theoretical model successfully explains the complex forces between moving liquid drops.
- Drop deformation and hydrodynamic lubrication are key factors influencing the measured forces.
- This work provides a framework for understanding droplet interactions in similar experimental conditions.