Water and Wastewater.com Help Forum - how to measure a spheres surface hydrophobic?

Water and Wastewater.com Help Forum - how to measure a spheres surface hydrophobicity?

Question
I am supposed to measure the anaerobic granules' surface hydrophobicity. but is there any method I can use to quantify it?
I only know the Contact Angle for plat surface and MATH for single cell.

Any suggestion is welcomed. Thanks!

First thoughts
If it is possible to dry the granules I would try one of the following approaches
# Washburn method, which was developed for contact angle measurements of powder packings, measures the height a liquid reaches due to capillarity. You may find a lot about this method at the internet, however, I doubt nobody has applied this method for anaerobic granules.
# related to the Wilhelmy method you might fix the individual granules to a tensiometer or alike and measure the force when the granules just contact the liquid surface and the change with time.

An elaborate method would be to measure the ad-/absorption in a mixture of liquids of different polarity.
Eventually the following could work, rinse the granules with alcohol and equilibrate them with a mixture of alcohol - octane
(or another mixture). Compare the initial liquid composition with that after equilibration.
Alternatively, use "inverse chromatography" (characterization of the stationary phase with the mobile phase). You can find a lot on this method at the internet.

Please send comments

just another, maybe more appropriate method

evaluation of packing density after sedimentation

after sedimentation the packing density achieved will be characteristic of surface polarity. Packing density should be determined straightforward in the natural media. Eventually repeated slight agitation of the sediment will be necessary to obtain reproducible packing density values. The more hydrophobic the surface, the more irregular (looser) will the packing due to the surfaces sticking together at the hydrophobic sites.


Further discussion

please consider, it will be difficult to test the surface properties without any alteration of the surface to some degree. This is also the case for the MATH method - contact with the hydrocarbon will to some extend "change the real surface properties of anaerobic granules since cell surface would be damaged".
Wilhelmy method is known as "Wilhelmy plate method" measuring the force at equilibrium for a wetting plate immersed in a liquid. From this one determines surface tension. What I meant was - if you have to types of granules with approx. the same volume, shape and density and contact them each with a liquid (water or organic solvent) the force acting on the granules will depend on their wetting properties (polarity).
Mixed adsorption - determine the concentration of the two components after equilibration - which component shows prefered sorption and to which extent. Lets say in an ethanol cyclohexane mixture I expect that ethanol will be depleted in the mixture due to prefered interaction with the cell surface. For the more hydrophobic granules depletion of ethanol will be less, for very hydrophobic granules eventually cyclohexane will be depleted.
Microsphere absorption method - you might work with a modification of that method. Use an reversed phase material of a filling material for chromatography - these materials are usually some kind of silica gel with grafted alkyl groups. You may also use silica gel or other solid powder (inorganic with negative surface charge or microcrystallin cellulose) wash them with a solution of a cationic surfactant and than with water, so you will get hydrophobic particles.
Sediment packing density is the ratio of volume of the particles (mass/density) and the volume of the sediment.

# ethanol-cyclohexane adsorption
please consider the different purpose
Kanyo et al. tried to gain exact adsorption isotherms over the whole range of composition of the mixed solvent. They had to use an analytical method which is able to detect even very small changes in composition.
Your purpose is a fast, qualitative characterization of surface hydrophobicity.
I dont know if 10 or 30 minutes will be more appropriate.
One or two initial composition will suffice. They have to be chosen in a range where the shift in concentration is expected to be high, i.e. for preferential adsorption of ethanol at lower ethanol concentration.
Another way to obtain well detectable changes in compositon is to use a high solid (surface) to solvent ratio. Eventually, most simply put the granules in a column and fill it with the mixed solvent and drain it off after a distinct time period. Gas chromatography would be a simple analytical method.

# fluorescence
'fluoresent hydrophobic solvent' will not have high activity, polyaromatic hydrocarbons as pyrene, have high flourescence activity but can only be dispersed, lets say after introduction via an ethanol or acetone solution. It seems difficult to me to use this to measure surface hydrophobicity.