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Interfacial Phenomena

Interfacial Phenomena. Interface:  boundary between 2 immiscible phases. NB: it is not present between miscible liquids properties of molecules at the interface differs from molecules in the bulk . Surface  boundary between solid/ gas or liquid/ gas. net inward pull. Surface tension:

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Interfacial Phenomena

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  1. Interfacial Phenomena

  2. Interface: • boundary between 2 immiscible phases. • NB: it is not present between miscible liquids • properties of molecules at the interface differs from molecules in the bulk. • Surface •  boundary between solid/ gas or liquid/ gas.

  3. net inward pull. Surface tension:  force per unit length acting parallel to the surface to counter balance the net inward pull. Interfacial tension:  tension existing at theinterface between 2 immiscible liquids. N.B. = zero in case of completely miscible liquids e.g. alcohol and water) • Units of surface tension: • = F/L  dyne/cm

  4. Surfactant = surface active agent Polar head Polar Ex: Water , glycerin Non Polar Ex: oils, lipids Non Polar tail

  5. CMC Critical Micelle Concentration (CMC)

  6. Measurement of Surface Tension: • Several methods are such as: • Capillary rise method • 2. Drop fall method = Drop weight method = Drop number method

  7. 2- The Drop Fall method: The drop weight method: The drop number method: using Stlagmometer 1- fill with water , count drops between the 2 marks  n water 2- 20ml in beaker , fill the liquid , count drops  n liquid

  8. Determination of critical micelle concentration (CMC) Surface tension method: 0.02% 0.04% 0.08% 0.16% 0.2% 0.24% Determine surface tension of each concentration using stlagmometer

  9. water=72.8 dyne/cm CMC

  10. Precautions: • Try the stlagmometerwith the highest concentration of SAA solution , If stream  change stlagmometer • Avoid air bubbles (withdraw slowly from deep inside the beaker) • Put the stalagmometerin verticalposition. • Receive fallen drops in your beaker • Use the same stlagmometerfor both liquid and water ( if broken????) • Don’t wash the stlagmometer when moving from low to high concentraions. • Your finger is away while counting.

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