1. Long Range Interactions beyond first neighbour
Intermolecular forces organizing complex fluids
…Laboratory experiments for challenging predictive theories.
2. The equation state of colloids: Jean Perrin‘s living heritage

2. Jean Perrin (1870-1942) Nobel prize 1926
"for his work on the discontinuous structure of matter, and especially for his discovery of sedimentation equilibrium".

3. van’t Hoff Raoult equivalence
Independant of the « size » of the dissolved « molecules »: till...?

4. The practical scales of osmotic pressure
They are expressed in diferent units depending on the different specialities using colloidal samples !
J. Wolfe, and
G. Bryant (1984)

5. Controlled humidity, membrane or capillary rise
H.R. = P/P0 = asolvant
 = P-P’ = s.g.h
… or analytical tonometry or … industrial devices such as « DVS »

6. … back to the van der Waals equation of state
And adding gravity ! Expecting a « colloidal atmosphere »: 6 km to micrometer scale jump !
Jean Perrin Nobel prize work « Les atomes »

7. Is this possible with « macroscopic atoms »?
Sedimenation equilibrium of emulsions Compares kinetic energy during Brownan motion in the absence of any convection To known gravitational energy
Jean Perrin Nobel price work (1908)

8. The air and the colloid « atmosphere » :
Column of air equation : Column of colloids equation
Jean Perrin « Les atomes »

9. How to produce « macroscopic atoms »?
From cascade fractionated crystallisation (initial method) (or later Zsigismondy using monodisperse gold colloids)
Jean Perrin « Les atomes »

10. Measurement of radius and density of colloids:
Three methods for sizing : Measure in projection after adsorption (HCl 0.01M) Weight after weak adsorbtion Stokes law on « falling cloud » constant friction 6 p e a v = V(D-d) g Three methods for particle density determination : Picnometry : fill the same container/evaporate melt and determine density of melt add KBr till matching centrifuge Results: radius = 0.37 micrometre and D= 1.195
Jean Perrin « Les atomes »

11. Observing macroscopic atoms sedimentation ?
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Jean Perrin « Les atomes »

12. Observing macroscopic atoms sedimentation ?
Moving the objective Large aperture Inserting an iris Statistics with time… Produces the result :
Jean Perrin « Les atomes »

13. Observing macroscopic atoms sedimentation ?
Moving the objective Large aperture Inserting an iris Statistics with time… Produces the raw data :
Jean Perrin « Les atomes »

14. The colloid atmosphere above layered dense packing
Deviations are important ! Why ?
N. Johnston and L G Howell : sedimentation equilibria of colloidal particles (1930)

15. What happens with charged (Br-st) latex ?
Gravity negligible: No sedimentation Strong repulsion : distance between colloids can be accessed via USAXS in liquid phase or SLS colloidal crystal
V. Reus, TH.Z and H. Versmold ( )

16. Method for estabishing EOS
Combining USAXS and membrane osmosis
references

17. Experimental results fits fully to Posson-Boltzmann?
The osmotic pressure gives the number of »effective » charges, i.e. the number of counter-ions per latex in each Voronoi cell (titrable stuctural charge : 12000)
V? Resu, ThZ and H. Versmold Equation of staet of charged latex suspensions( )

18. What happens when multi-charged co-ions are added ?
A drastic reduction of the osmotic pressure ! 
V. Reus et al.: Fusion of colloidal crystals induced by monovalent and asymmetric salt: an osmotic pressure and USAXS (1999)

19. What happens when salt is added in the reservoir?
A R eeductionof the osmotic pressure sicne screening length << interlatex distance 
V. Reus et al.: Fusion of colloidal crystals induced by monovalent and asymmetric salt: an osmotic pressure and USAXS (1999)

20. What happens when multi-charged co-ions are added ?
A drastic reduction of the osmotic pressure ! 
V. Reus et al.: Fusion of colloidal crystals induced by monovalent and asymmetric salt: an osmotic pressure and USAXS (1999)

21. General result of EOS determination of charged monodisperse bromosturence latex :
Mechanism: salt depletion from colloidal crystals is due to co-ion depletion and can reduce the stability (osmotic pressure) of a colloidal crystal even below micromolar concetration? Corrolario: Suspected Long range attractive elctrostatic potentials are an artefact due to slow relase of not cross-linked poly-ions

22. What we have learnt :
Measuring EOS is a way to test intensity and decay length of any type colloidal interaction As well as its dependance to chemical enviropnnment ( T, pH, solutes… even surfactants
F. Evans and H. Wennerström : The colloidal domain: