You can use techniques such as mercury intrusion porosimetry, liquid extrusion porosimetry and gas adsorption techniques for pore size distribution characterization.

Another method would be to use microCT and nanoCT but they are not easily accessible. In addition to mercury intrusion, liquid extrusion and microCT, we have performed image processing on SEM images to characterize surface porosity. Read this for more details:

Fabrication and characterization of three-dimensional macroscopic all-carbon scaffolds, Carbon, In Press.

http://www.sciencedirect.com/science/article/pii/S0008622312008482

The porosity is the ratio vacuum/ material. One method to measure is gravimetric: You weight the sample before, after the porous layer formation and after to have removed the porous layer.

An other method is an optical method if you know the material of your porous layer you know also the dielectric constant . You collect the reflectivity spectra of you porous layer an using a model ( effective medium aproximantion like Brugman or Looyenga for porous material) knowing the porous layer thikness is possible to determine, by the fit, the porosity

if your coatings are not much costly then scratch-off it and do BET.

dye adsorbtion/desorbtion method is usually employed in dye sensitized solar cells. Of course it depends on the coating you have. If you have at least 100mg of material then you may be able to do BET

Adsorption/desorption isotherms with nitrogen

we have tried for using BET for membrane with thickness ~40micro. I think you can try it.

go for BET analysis..........

Thank you all for all the suggestions. The reason why we want to know the layer's porosity is that we don't know the exact mass of the layer or the coating. I suppose it is < 1 mg. Thus, BET is not an option , as we don't know the exact mass of the layer, which should be much less than the mass of the substrate. Also, since scratching will partly change or damage the structure of the thin layer as well as the porosity , so I also don't think that is a good way to go. Dye adsorbtion/desorbtion method sounds somehow promising. Can you get me a link or a reference paper of that.

Thank you!

Rutherford Backscattering Spectroscopy(RBS) Will give you thé information If you know the thickness and composition.

Micro CT is another alternative since you don not have the mass and if you dont have the composition and thickness

If BET not an option, just weight it.

since your sample is thin film mounted on a substrate, porosity can be measured by GISAXS method.. grazing incidence SAXS..

Another method is ellipsometric porosimetry.. but the value of porosity depends on the choice of adsorbent.

Adsorption or desorption isotherms in gaseous media. Amount of material you need depends on technique you possess.

here are few links regarding papers on dye absorbtion/desorbtion on TiO2. depending on the material you have, you will have to change the dye. All you need is a dye which is well absorbed by your material, an UV-Vis Spectrometer and you need to know the footprint (how much space is occupied by a molecule) of the dye

http://pubs.rsc.org/en/content/articlelanding/2012/jm/c2jm30481c

http://pubs.acs.org/doi/abs/10.1021/cm980303g (N719 dye footprint as an example)

www.rsc.org/suppdata/nr/c2/.../c2nr31127e.pdf

hope this helps

Last link was wrong sorry! Here is the right one! :-)

http://www.rsc.org/suppdata/nr/c2/c2nr31127e/c2nr31127e.pdf

Porosity could be measured by using instrument known as porosometer. The technique is based on Helium gas adsorption.

It could be also measured by using Azobenzne dye adsorption technique.

It is possible to measure the porosity of the thin film or layer of posorus material by Hyperpolarized Xe-129 NMR spectroscopy. I am attaching a file for your reference.

you can try Hg pososimeter, but I don´t know if the accuracy is high enough for a such task...

You can use DRS measurement by fitting reflection data in Lorentz-Lorenz equation.

Please Mahmoud Zendehdel can you explain more about DRS measurment. do recommend some papers.

Nebatti Abdelkader, You can refer to Dr Boschloo article (J. Phys. Chem. B 1999, 103, 2228) or for more details you can refer to "Principles of Optics" (Born, M and Wolf, E; Pergammon Press, 1975).

@Mahmoud Zendehdel, Thank you.

Using thin film transmission measurements one can get porosity.

Rathinam Chandramohan

Why wouldn't BET work?

If the sample is a composite, run the BET on the support first.

Then run the BET on the composite.

You may have to cut your sample(s) into thin slivers to get them into the BET cell.

Note that the more you have, the better the measurement - so long as the sample isn't packed tightly.

Note also that porosity and surface area are 2 very different quantities!

And while porosimetry is related to the porosity, the connection between the two is not so straightforeward unless you have a lot of data.

Porosity is a simple quantity and is defined by the void space withing a volume element of the structure, usually as a percentage or fraction of the total volume.

But porosimetry is ultimately used to measure pore size distributions.

NMR Cryoporometry - Stack/roll a number of layers to fill a 2.5mm diameter tube - NMR Cryoporometry is the constant pressure version of the Gibbs Equations, where gas adsorption is the constant temperature version.

NMRC works well on such porous films, and is now our preferred method.

See : http://www.lab-tools.com ; http://www.nano-metrology.co.uk/

http://en.wikipedia.org/wiki/Thermoporometry_and_cryoporometry#Nuclear_magnetic_resonance_cryoporometry

Nuclear Magnetic Resonance Cryoporometry J. Mitchell, J. Beau W. Webber and J.H. Strange. Physics Reports, 461, 1-36, 2008. DOI: 10.1016/j.physrep.2008.02.001

Hi as mentionned previously by Antoni Peters I recommend you to test BET (S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc., 1938, 60, 309. doi:10.1021/ja01269a023) on your samples. For Specific Surface is well adpated and from the set of data obtained by BET you can estimate some porosity distribution. You should keep in mind that SS and bulk porosity are more or less linked but BET is surface adsoprtion then volumic one for open porosity and theire is a slight difference between open and closed or not accessible porosity. I hope this answer will help you

You can use ASAP 2020 from Micromeritics if you have 100-150 mg of test material

Dear Dr Wei,

It's a tardy reply but maybe helpful: you can make a realistic estimate of porosity and surface area based on my paper "Surface area and pore volume of a system of particles as a function of their size and packing" published in Microporous and Mesoporous Materials 122 (2009) 234–239. Today I've added it to my ResearchGate profile together with a supplementary Origin file enabling one to perform proper calculations.

All best,

S.K.

Fouzia Zoukrami

The specific surface area can be evaluated by two parameters linear BET plot in the range P/P0 of 0.01-0.2 and by T-curve method ,

in the other hand the BJH method based on the Kelvin equation can be applied to evaluate pore size distribution by desorption branch

so to obtain these parameters , you can using a Micrometric ASAP2010 apparatus ( static volumetric technique)

Dear Dr.Wei Wei. We always measure specific surface area of nanocoating by BET (ASAP 2020, Micromeritics) without problem, when we have enough area of thin subsrate (as example porous Si on Si waffer - just cracking substrate to 5x5 mm for standard ASAP bulb...)