1. 10. 3 Effective interaction Area of two spheres
10.3 Effective interaction Area of two spheres : The Langbein Approximation
The effective area of interaction of a sphere
with a surface = the circular zone centred at a
distance–D from the surfaces( inside the sphere )
for n=6
The interaction of a sphere and a surface
= the same as that of two planar surfaces at the same surface separation D

2. 10.4 Interactions of large bodies compared to those between molecules
For two macroscopic bodies, the interaction energy generally decays much more slowly with distance
 the van der Waals energy between large condensed bodies decays is effectively of much longer range

3. 10.4 Interactions of large bodies compared to those between molecules
In contact b/n a small molecule and a wall
In contact b/n a sphere of atomic dimensions
In contact b/n two spheres
Increasing of the size of a sphere above atomic dimensions

4. 10. 5 Interaction Energy and Interaction
10.5 Interaction Energy and Interaction Forces : Derjagun Approximation
[ Assumption ]
Two large spheres of radii R1 and R2
R1>>D and R2>>D
By integrating the force between small circular regions of area on one surface
Surface to be locally flat

5. 10. 5 Interaction Energy and Interaction
10.5 Interaction Energy and Interaction Forces : Derjagun Approximation
The force b.t.n two spheres is expressed in terms of the energy per unit area of two flat surfaces at the same separation D
The distance dependence of the force b.t.n two curved surfaces can be quite different from that b.t.n two surfaces even though the same type of force is operating in both.

6. Fig. 10. 4 Force laws betweem two curved
Fig Force laws betweem two curved surfaces and two flat surfaces
Useful theoretical tool to derive

7. 16.1 Indirect access for W(D)
Thermodynamic data on gases, liquids and solids
Physical data
on gases, liquids and solids
Thermodynamic data on liquids and liquid mixtures
PVT data, B.P
Latent heats of vaporization
lattice energy
Viscosity, diffusion. Compressibility, NMR X-ray, molecular beam scattering experiment
Phase diagrams
solubility
Partitioning, miscibility
osmotic pressure
Short-range attractive potentials b.t.n molecules
Short-range interactions of molecules, especially repulsive forces giving molecular size, shape and structural role in condensed phase
Short-range silute-solvent and solute-solute interactions
Useful theoretical tool to derive

8. 16.2 Direct access for W(D)
Useful theoretical tool to derive

9. Practical Applications
16.2 Direct access for W(D)
Types
Practical Applications
Information
Adhesion measurement
Xerography, particle adhesion. Powder technology, ceramic processing
Particle adhesion forces and the adhesion energies of solid surfaces in contact ( attractive short-range forces)
Peeling measurement
Adhesive tapes, material fracture and crack propagation
Force-measuring spring or balance
Testing theories of intermolecular forces
The force macroscopic surfaces as a function of surface separation
The full force law of an interaction
Useful theoretical tool to derive

10. Practical Applications
16.2 Direct access for W(D)
Types
Practical Applications
Effects
Contact Angle
Testing wettability and stability of surface films, foams
Liquid-Liquid or Liquid-Solid adhesion energy
Information of states and adsorbed films, and of molecular reorientation time at interfaces
Equilibrium thickness of thin free films
Soap films, foams
A function of salt conc. or vapour pressure
The long-range repulsive forces stabilizing thick wetting films
Equilibrium thickness
of thin absorbed films
Wetting of hydrophilic surface by water, adsorption of molecules from vapor, protective surface coatings and lubricant layers, photographic films
Useful theoretical tool to derive

11. Practical Applications
16.2 Direct access for W(D)
Types
Practical Applications
Effects
Interparticle spacing in liquids
Colloidal suspensions, paints, pharmaceutical dispersions
The interparticle forces
By changing the solution conditions and their mean separation
By changing the quantity of solvents
Limits to measure only the repulsive parts
Sheet-like particle spacing in liquids
Clay and soil swelling behavior, microstructure of soaps and biological membranes
Coagulation studies
Basic experimental technique for testing the stability of colloidal preparations
Information on the interplay of repulsive and attractive forces between particles in pure, sulfactant and polymer solutions
Useful theoretical tool to derive

12. 10.7 Direct measurements of Surface and Intermolecular Forces
The most unambiguous way to measure a force-law
 to position two bodies close together and directly measure the force between them
 very straightforward
 very weak challenge coming at very small intermolecular interaction
 surface separation controlled and measured to within 0.1nm
Useful theoretical tool to derive

13. The Surfaces Forces Apparatus (SFA)
Measuring surface forces in controlled vapor or immersed in liquids is directly measured using a variety of interchangeable force-measuring springs
Both repulsive and attractive forces are measuring and a full force law can be obtained over any distance regimes
Useful theoretical tool to derive

14. The Surfaces Forces Apparatus (SFA)
The distance resolution about 0.1nm (angstrom level)
the force sensitivity about 10-8 N
In Surfaces
Two curved molecularly smooth surfaces of mica in a crossed cylinder configuration
The separation is measured by use of an optical technique using multiple beam interference fringes
The distance is controlled by use of a three-stage mechanism of increasing sensitivity ( the coarse control 1µm – the medium control 1nm – a piezoelectric crystal tube 0.1nm )
Useful theoretical tool to derive

15. The Surfaces Forces Apparatus (SFA)
The force measurement
The force A measured by expanding or contracting the piezoelectric crystal by a known amount
The force B measured by optically how much the two surfaces have actually moved
The difference of force b.t.n two positions
= [ Force A – force B ] * the stiffness of the force-measuring spring
Useful theoretical tool to derive

16. The Surfaces Forces Apparatus (SFA)
The force and the interfacial energy
The force b.t.n two curved surfaces scale = R
The adhesion or interfacial energy E per unit area two flat surfaces
by the Derjaguin approximation
For given R and sensitivity F,
getting E ( an interfacial energy)
Useful theoretical tool to derive

17. The Surfaces Forces Apparatus (SFA)
The use of SFA
Identifying and quantifying most of fundundamental interactions occuring between surfaces on both aqueous solutions and nonaqueous liquids
Including the attractive van der Waaals and repulsive electrostatic ‘double –layer’ forces, oscillatory forces, repulsive hydration forces, attractive hydrophobic forces, steric interactions involving polymeric systems and capillary and adhesion
The extension of measurement into dynamic interaction and time-dependent effects and the fusion of lipid bilayers . etc
Useful theoretical tool to derive

18. Total Internal Reflection Microscopy(TIRM)
Measuring minute forces( <10-15 N) between a colloidal particle and a surface
Measuring the distance between an individual colloidal particle of diameter ~10 µm hovering over a surface.
A laser beam is directed at the particle through the surface made of transparent glass
From the intensity of reflected beam
deducing the equilibrium separation D0
Providing data on interparticle interactions under conditions closely paralleling those occurring in colloidal systems
Useful theoretical tool to derive

19. The Atomic Force Microscope(AFM)
Measuring atomic adhesion forces (10-9~10-10 N) between a fine molecular-sized tip and a surface ( 1µm < Tip radii < atom size )
At finite distances, using very sensitive force-measuring springs (spring stiffness=0.5 Nm-1) and very sensitive ways for measuring the displacement (0.01nm)
very short-range forces , but not longer range forces
Interpreting the results is not always straightforward and exact due to the tip geometry
Useful theoretical tool to derive