fluid interface atomic force microscopy fi afm n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Fluid Interface Atomic Force Microscopy (FI-AFM) PowerPoint Presentation
Download Presentation
Fluid Interface Atomic Force Microscopy (FI-AFM)

Loading in 2 Seconds...

play fullscreen
1 / 12

Fluid Interface Atomic Force Microscopy (FI-AFM) - PowerPoint PPT Presentation


  • 111 Views
  • Uploaded on

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).

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Fluid Interface Atomic Force Microscopy (FI-AFM)' - colton


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
fluid interface atomic force microscopy fi afm
Fluid Interface Atomic Force Microscopy(FI-AFM)

D. Eric Aston

Prof. John C. Berg, Advisor

Department of Chemical Engineering

University of Washington

slide2

Fluid Interface AFM (FI-AFM)

Gain knowledge about oil agglomeration and air flotation through studies of single particle/oil-drop interactions.

Air Flotation

Oil Agglomeration

Quantify the influence of non-DLVO forces on colloidal behavior:

Colloidal AFM

1. Hydrophobic attraction

2. Hydrodynamic repulsion

3. Steric, depletion, etc.

Ultimately, standardize an analytical technique for colloidal studies of fluid-fluid interfaces with AFM.

slide3

Dzc

kc · Dzc = F

F(S)

S = ?

Dzd

kd(Dzd) · Dzd = F

Oil

Dz

hydrophobic effects

steric effects

Interfacial tension

effects

Objectives for Deforming Interfaces

Determine drop-sphere separation with theoretical modeling.

Proper accounting of DLVO and hydrodynamic effects

slide4

Photodetector

Optical objective

He-Ne laser

Glass walls

Water

Oil

x-y-z

Scanner

AFM Experimental Design

Direct interfacial force measurements with AFM.

Prove AFM utility based on theoretical modeling.

AFM F(z) Data

Classic Force Profile

F/R

Force

Displacement (mm)

Separation (nm)

exact solution for droplet deformation

r

z

Exact Solution for Droplet Deformation

Drop profile calculated from augmented Young-Laplace equation: includes surface and body forces.

The relationship between drop deflection and force is not fit by a single function.

AFM probe

F

fluid

medium

Do

P(z(r))

D(r)

Po

k(r,z)

slide6

Qualitative Sphere-Drop Interactions

Several properties affect drop profile evolution:

1. Initial drop curvature

2. Particle size

3. Interfacial tension

4. Electrostatics

5. Approach velocity

Water

Oil

Liquid interface can become unstable to attraction.

DP > Po

DP = Po

Drop stiffness actually changes with deformation:

  • Weakens with attractive deformation.
  • Stiffens with repulsive deformation.
long range interactions in liquids
Long-Range Interactions in Liquids

van der Waals interaction - usually long-range attraction.

Includes hard

wall repulsion

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.

Empirical fit

slide8

Rd = 250 mm

Rs = 10 mm

A132 = 5 x 10-21 J

= = -0.25 mC/cm2

|v| = 100 nm/s

s = 52 mN/m

Drop Stiffness

Film Thickness

As These Increase

Drop radius, Rd

Particle radius, Rs

Approach velocity, |v|

Interfacial tension, s

Electrolyte conc.

Surface charge,

decreases

increases

increases

increases

~constant

~constant

constant

increases

increases

decreases

decreases

increases

Theoretical Oil Drop-Sphere Interactions

Polysytrene/Hexadecane in Salt Solutions

[NaNO3]

oil ps experimental profiles

Rd = 250 mm

Rs = 10 mm

A132 = 5 x 10-21 J

= = -0.32 mC/cm2

|v| = 120 nm/s

s = 52 mN/m

Oil-PS Experimental Profiles

0.1 mM NaNO3

Hydrophobic effect

C1 = -2 mN/m

l = 3 nm

slide10

Dynamic Interfacial Tension - SDS

  • Oil-water interfacial tension above the CMC for SDS decreases with continued deformation of the droplet.

6 mN/m

Fit

slide11

Oil Drop with Cationic Starch Adlayers

  • Cationic starch electrosterically stabilizes against wetting.
  • Even at high salt, steric hindrance alone maintains stability.

DP < Po

DP = Po

Long-range attraction without wetting = depletion?

0.1 M NaNO3

  • What is the minimum adlayer condition for colloid stability?
  • Why does cationic starch seem not to inhibit air flotation?
slide12

Conclusions

  • Expectation of a dominant hydrophobic interaction is premature without thorough consideration of the deforming interface.
  • Several system parameters are key for interpreting fluid interfacial phenomena, all affecting drop deformation.

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

  • FI-AFM greatly expands our ability to explore fluid interfaces on an ideal scale.