1 / 44

The Colloidal Dynamics ZetaProbe

Colloidal Dynamics - leaders in colloid measurement. 2. Zeta Potential of Concentrated Colloids. . . Colloidal Dynamics ZetaProbe. ZetaProbe Features

Mia_John
Download Presentation

The Colloidal Dynamics ZetaProbe

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. Colloidal Dynamics - leaders in colloid measurement 1 The Colloidal Dynamics ZetaProbe

    2. Colloidal Dynamics - leaders in colloid measurement 2 Zeta Potential of Concentrated Colloids

    3. Colloidal Dynamics - leaders in colloid measurement 3 Colloids-background information Colloids are suspensions of particles in fluids. The particles are typically less than one micron in diameter. Examples include paints, inks, paper coatings, milk, blood, plus many pharmaceutical and food products

    4. Colloidal Dynamics - leaders in colloid measurement 4 Particle charge Colloidal particles are electrically charged The charge can be controlled by various means, including pH adjustment Each particle is surrounded by a diffuse cloud of ions of opposite charge

    5. Colloidal Dynamics - leaders in colloid measurement 5 The double layer Diffuse cloud + surface charge= double layer

    6. Colloidal Dynamics - leaders in colloid measurement 6 The Zeta Potential

    7. Colloidal Dynamics - leaders in colloid measurement 7 Thickness of the diffuse layer Diffuse layer thickness ?- -1 given by

    8. Colloidal Dynamics - leaders in colloid measurement 8 The importance of ? potential Zeta potential affects rheology filtration/ dewatering shelf life colloid stability and zeta is a measure of the surface chemistry (eg the type of coating on the particle)

    9. Colloidal Dynamics - leaders in colloid measurement 9 Inter-particle force depends on ?

    10. Colloidal Dynamics - leaders in colloid measurement 10 The importance of ? - cont’d

    11. Colloidal Dynamics - leaders in colloid measurement 11 Zeta Potential (cont’d)

    12. Colloidal Dynamics - leaders in colloid measurement 12 Zeta potential- cont’d Particles form elastic networks

    13. Colloidal Dynamics - leaders in colloid measurement 13 Zeta potential- cont’d The porosity and strength of floc affects filtration and dewatering

    14. Colloidal Dynamics - leaders in colloid measurement 14 Controlling zeta potential Zeta depends on pH and electrolyte concentration, surfactant, polyelectrolyte...

    15. Colloidal Dynamics - leaders in colloid measurement 15 The Trouble with Dilution Most devices for measuring size and zeta only work on very dilute colloids So most samples require a lot of dilution Dilution is time consuming, and you can easily alter the zeta potential by the dilution.

    16. Colloidal Dynamics - leaders in colloid measurement 16 The problem with dilution Example: Alumina sample diluted with DI water

    17. Colloidal Dynamics - leaders in colloid measurement 17 Why did dilution alter zeta? Because both pH and ionic strength changed.

    18. Colloidal Dynamics - leaders in colloid measurement 18 Trouble with dilution- cont’d The very dilute samples are easily contaminated by surface active materials

    19. Colloidal Dynamics - leaders in colloid measurement 19 Measuring without dilution Colloidal Dynamics has developed and patented at technique known as Electroacoustics for measuring Zeta Potential in concentrated colloids

    20. Colloidal Dynamics - leaders in colloid measurement 20 Electroacoustic Measurement Technique

    21. Colloidal Dynamics - leaders in colloid measurement 21 Measuring ESA in the ZetaProbe Probe sits in bottom-stirred cell

    22. Colloidal Dynamics - leaders in colloid measurement 22 Dynamic mobility

    23. Colloidal Dynamics - leaders in colloid measurement 23 Getting dynamic mobility from ESA

    24. Colloidal Dynamics - leaders in colloid measurement 24 Why is ESA linked to zeta?

    25. Colloidal Dynamics - leaders in colloid measurement 25 Why is ESA linked to size?

    26. Colloidal Dynamics - leaders in colloid measurement 26 Typical mobility spectra

    27. Colloidal Dynamics - leaders in colloid measurement 27 Getting size and ? from mobility Where ?th is theoretical mobility, a known function of size and ? p(a) is particle size distribution function. We adjust p(a) and ? to get best fit of mobility spectrum

    28. Colloidal Dynamics - leaders in colloid measurement 28 Mobility Spectra of several silica slurries

    29. Colloidal Dynamics - leaders in colloid measurement 29 ZetaProbe Advantage #3 –particle size With the ZetaProbe you don’t need to enter particle size In most colloids Dynamic Mobility given by

    30. Colloidal Dynamics - leaders in colloid measurement 30 Colloidal Dynamics Measurements In Concentrated Systems

    31. Colloidal Dynamics - leaders in colloid measurement 31 Spectra for dilute and concentrated silica

    32. Colloidal Dynamics - leaders in colloid measurement 32 Experimental procedures To test the measurements, need to make up samples in which zeta and size stay constant as concentration is varied. This involves diluting concentrated, thin double-layer systems and keeping the background electrolyte the same.

    33. Colloidal Dynamics - leaders in colloid measurement 33 Supporting evidence- a careful dilution Alumina study by Johnson, Russell & Scales

    34. Colloidal Dynamics - leaders in colloid measurement 34 Supporting evidence -cont’d Alumina study by Johnson, Russell & Scales- cont’d

    35. Colloidal Dynamics - leaders in colloid measurement 35 Rheology depends on zeta This slide presents rheological measurements made on the same slurries presented in slides 3& 4. Measurements of the shear yield stress of the slurry were made at each pH and volume fraction. The shear yield stress is the max shear stress that can be sustained in the slurry without setting the suspension into motion. At the iep the attractive forces between the particles in the floc reach maximum, and so the shear yield stress peaks at this point. The shear yield stress also increases with particle concentration which decreases the average particle separation distance. As the zeta is increased, the electrostatic repulsion should increase (for small zeta) like zeta^2. This slide presents rheological measurements made on the same slurries presented in slides 3& 4. Measurements of the shear yield stress of the slurry were made at each pH and volume fraction. The shear yield stress is the max shear stress that can be sustained in the slurry without setting the suspension into motion. At the iep the attractive forces between the particles in the floc reach maximum, and so the shear yield stress peaks at this point. The shear yield stress also increases with particle concentration which decreases the average particle separation distance. As the zeta is increased, the electrostatic repulsion should increase (for small zeta) like zeta^2.

    36. Colloidal Dynamics - leaders in colloid measurement 36 Rheology vs zeta- cont’d In this slide, the yield stress data for the alumina slurries presented in the previous slide is plotted in a different way. Here we show a plot of the normalised shear yield stress vs zeta^2, where zeta is obtained from the AZR measurements shown earlier in slide 4. The normalized shear yield stress is the shear yield stress divided by the maximum yield stress (tymax). Scales and colleagues show that t/tmax= 1-B*zeta^2, where t is the yield stress and tmax is the value at the iep. They derive a formula for B in terms of the Hamaker constant and the closest approach of the particles. The fact that the lines all collapse (to within expt error) onto the one line is a verification that the zeta we measure in a concentrated suspension is indeed the real zeta. This curve is a graphic demonstration that zeta determines suspension rheology for electrostatically stabilized slurries. DLVO theory predicts that the inter-particle electrostatic force is proportional to the square of the zeta potential. In this slide, the yield stress data for the alumina slurries presented in the previous slide is plotted in a different way. Here we show a plot of the normalised shear yield stress vs zeta^2, where zeta is obtained from the AZR measurements shown earlier in slide 4. The normalized shear yield stress is the shear yield stress divided by the maximum yield stress (tymax). Scales and colleagues show that t/tmax= 1-B*zeta^2, where t is the yield stress and tmax is the value at the iep. They derive a formula for B in terms of the Hamaker constant and the closest approach of the particles. The fact that the lines all collapse (to within expt error) onto the one line is a verification that the zeta we measure in a concentrated suspension is indeed the real zeta. This curve is a graphic demonstration that zeta determines suspension rheology for electrostatically stabilized slurries. DLVO theory predicts that the inter-particle electrostatic force is proportional to the square of the zeta potential.

    37. Colloidal Dynamics - leaders in colloid measurement 37 Concentrated emulsion example Zeta potential vs concentration Emulsion diluted with true supernatant

    38. Colloidal Dynamics - leaders in colloid measurement 38 ZetaProbe Advantage: automated titrations Fast and accurate titration measurement

    39. Colloidal Dynamics - leaders in colloid measurement 39 ZetaProbe advantage: Accurate IEP Example of auto background correct: Measurements on 1 and 2 wt% Titania- no background correction

    40. Colloidal Dynamics - leaders in colloid measurement 40 ZetaProbe Advantage: accurate IEPcont. With auto background correct

    41. Colloidal Dynamics - leaders in colloid measurement 41 Optimizing Dispersant Dose

    42. Colloidal Dynamics - leaders in colloid measurement 42 Optimizng additive dosages Addition of Darvan C polyelectrolyte to Alumina as function of pH Zeta depends on pH and polyelectrolyte concentration When zeta depends on more than one parameter- manual titration would be very time consuming With the ZetaProbe, complete surface characterization can be completely rapidly

    43. Colloidal Dynamics - leaders in colloid measurement 43 Monitoring non-ionic polymer adsorption Nonionic polymer on silica Zeta drops because hydrodynamic slipping plane moves further from particle surface

    44. Colloidal Dynamics - leaders in colloid measurement 44 Studying particle coatings iep changes with alumina coating; hence, iep can be used to monitor surface coating

    45. Colloidal Dynamics - leaders in colloid measurement 45 Summary The ZetaProbe is a fast and powerful tool for zeta potential measurements and surface chemistry characterization The ability to measure directly in concentrated samples ensures accurate zeta potential values Automated titrations provide enormous productivity advantage over traditional optical methods that require dilution

More Related