Fluid Interface Atomic Force Microscopy (FI-AFM). D. Eric Aston Prof. John C. Berg, Advisor Department of Chemical Engineering University of Washington. Fluid Interface AFM (FI-AFM).
D. Eric Aston
Prof. John C. Berg, Advisor
Department of Chemical Engineering
University of Washington
Gain knowledge about oil agglomeration and air flotation through studies of single particle/oil-drop interactions.
Quantify the influence of non-DLVO forces on colloidal behavior:
1. Hydrophobic attraction
2. Hydrodynamic repulsion
3. Steric, depletion, etc.
Ultimately, standardize an analytical technique for colloidal studies of fluid-fluid interfaces with AFM.
kc · Dzc = F
S = ?
kd(Dzd) · Dzd = F
Objectives for Deforming Interfaces
Determine drop-sphere separation with theoretical modeling.
Proper accounting of DLVO and hydrodynamic effects
AFM Experimental Design
Direct interfacial force measurements with AFM.
Prove AFM utility based on theoretical modeling.
AFM F(z) Data
Classic Force Profile
Several properties affect drop profile evolution:
1. Initial drop curvature
2. Particle size
3. Interfacial tension
5. Approach velocity
Liquid interface can become unstable to attraction.
DP > Po
DP = Po
Drop stiffness actually changes with deformation:
van der Waals interaction - usually long-range attraction.
Electrostatic double-layer - often longer-ranged than dispersion forces.
Moderately strong, asymmetric double-layer overlap
Hydrodynamic lubrication - Reynolds pseudo-steady state drainage.
* Added functionality for varied boundary conditions
Hydrophobic effect - observed attraction unexplained by DLVO theory or an additional, singular mechanism.
Rs = 10 mm
A132 = 5 x 10-21 J
= = -0.25 mC/cm2
|v| = 100 nm/s
s = 52 mN/m
As These Increase
Drop radius, Rd
Particle radius, Rs
Approach velocity, |v|
Interfacial tension, s
Theoretical Oil Drop-Sphere Interactions
Polysytrene/Hexadecane in Salt Solutions
DP < Po
DP = Po
Long-range attraction without wetting = depletion?
0.1 M NaNO3
1. Surface forces - DLVO, hydrophobic, etc.
2. Drop and particle size - geometry of film drainage
3. Interfacial tension - promotion of film drainage
4. Approach velocity - resistance to film drainage