1 / 12

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. Fluid Interface AFM (FI-AFM).

colton
Download Presentation

Fluid Interface Atomic Force Microscopy (FI-AFM)

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Fluid Interface Atomic Force Microscopy(FI-AFM) D. Eric Aston Prof. John C. Berg, Advisor Department of Chemical Engineering University of Washington

  2. 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.

  3. 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

  4. 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)

  5. 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)

  6. 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.

  7. 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

  8. 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]

  9. 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

  10. Dynamic Interfacial Tension - SDS • Oil-water interfacial tension above the CMC for SDS decreases with continued deformation of the droplet. 6 mN/m Fit

  11. 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?

  12. 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.

More Related