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.
Slide 3
Surface tension: force per unit length acting parallel to the
surface to counter balance the net inward pull. Units of surface
tension: = F/L dyne/cm Interfacial tension: tension existing at the
interface between 2 immiscible liquids. N.B. = zero in case of
completely miscible liquids e.g. alcohol and water)
Slide 4
Polar Ex: Water, glycerin Non Polar Ex: oils, lipids Polar head
Non Polar tail Surfactant = surface active agent
Slide 5
Critical Micelle Concentration (CMC) CMC
Slide 6
Slide 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
Slide 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
Slide 9
Slide 10
CMC water= 72.8 dyne/cm
Slide 11
Precautions: Try the stlagmometer with the highest
concentration of SAA solution, If stream change stlagmometer Avoid
air bubbles (withdraw slowly from deep inside the beaker) Put the
stalagmometer in vertical position. Receive fallen drops in your
beaker Use the same stlagmometer for both liquid and water ( if
broken????) Dont wash the stlagmometer when moving from low to high
concentraions. Your finger is away while counting.