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Colloid: Electrokinetic properties

Colloid: Electrokinetic properties. Kausar Ahmad Kulliyyah of Pharmacy http://staff.iiu.edu.my/akausar. Contents. Electrokinetic phenomena. Potentials. Zeta potential.

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Colloid: Electrokinetic properties

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  1. Colloid:Electrokinetic properties Kausar Ahmad Kulliyyah of Pharmacy http://staff.iiu.edu.my/akausar Physical Pharmacy 2

  2. Contents Physical Pharmacy 2

  3. Electrokinetic phenomena Physical Pharmacy 2

  4. Potentials Physical Pharmacy 2

  5. Zeta potential • The slipping/ shear plane separates the thin layer of liquid bound to the solid surface(elastic behavior) from the rest of liquid (normal viscous behavior). • The electric potential at the shear plane is called zeta potential. From http://www.silver-colloids.com/Tutorials/Intro/pcs17.html Physical Pharmacy 2

  6. Determination of zeta potential • Measure electrophoretic mobility • the electrophoretic mobility is the ratio of the velocity of particles to the field strength Physical Pharmacy 2

  7. Traditional Measurement of Electrophoretic Mobility Physical Pharmacy 2

  8. Smoluchowski equation • From Marian Smoluchowski: m=ez/h m electrophoretic mobility e electric permittivity of the liquid • is the viscosity applies for • thin double layer • when the zeta potential is not too high • large colloidal particles and high ionic strengths Physical Pharmacy 2

  9. Huckel Equation • size of particle is small compared to EDL (or thick EDL) • Use Huckel equation: m=ez/1.5h Thickness of EDL, 1/κ Physical Pharmacy 2

  10. Complications in zeta potential determination Electrophoretic retardation Relaxation effect Physical Pharmacy 2

  11. Laser Doppler Velocimetry Young’s interference fringes formed at stationary level Using Fourier Transform, the correlator produces a frequency spectrum from which the mobility distribution and hence zeta potential are calculated. Physical Pharmacy 2

  12. Fluctuation in intensity of scattered light From: http://www.silver-colloids.com/Tutorials/Intro/pcs23.html Physical Pharmacy 2

  13. Advantages of laser technique Physical Pharmacy 2

  14. Examples of Application Physical Pharmacy 2

  15. Isoelectric point (IEP) • If pH<4 or pH>8 there is sufficient charge to confer stability. • If 4<pH<8 dispersion may be unstable. • Most unstable at around pH 6 (IEP) From: http://www.silver-colloids.com/ Tutorials/Intro/pcs18.html Physical Pharmacy 2

  16. Zeta potential of chloramphenicol and glass particles in benzethonium (+) chloride solution.- an adsorbing cation Charge reversal concentration From: Florence & Attwood Physical Pharmacy 2

  17. References RJ Hunter, Zeta Potential in Colloid Science, Academic Press (1988) RJ Hunter, Foundations of Colloid Science Volume 2, Clarendon Press Oxford (1989) ID Morrison & S Ross, Colloidal Dispersions, Wiley-Interscience, New York (2002) http://zeta-potential.sourceforge.net/ http://www.silver-colloids.com/Tutorials/Intro/pcs1.html http://www.luminet.net/~wenonah/riddick/chap22.htm Physical Pharmacy 2

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