1. Surface energy study γS : surface free energy of solid
γL : surface free energy of liquid
γSL : interfacial free energy between solid and liquid
θ: solid/liquid contact angle
Young‘s equation
γSL = γS - γL cosθ (1)
γSL = γS + γL - 2(γS γL) ½ (2)
from (1) (2)
γS = γL(1+cosθ)2/ (3)

2. γS : apolar component, accounting for Liftshitz/van der Waals
Fowkes first suggest that surface tension could resolved into component due to dispersion force, the induction and dipole-dipole forces, and hydrogen bonding
γS = γS + γS (4)
γS = 2 (γS +γS-) ½ (5)
γS = γS (γS +γS-) ½ (6)
γS : apolar component, accounting for Liftshitz/van der Waals
type interactions
γS : polar component, accounting for acid-base or donor-
acceptor type interactions
γS + : Lewis-acid component, electron acceptor
γS- : Lewis-base component, electron donor AB LW

3. Hydrogen bonding
We may compare the surface tension data of CHCl3 and CCl4 and interfacial tension vs. water and free energy of adhesion to water.
-ΔGaij = γi + γj - γij (7)
-ΔGaij : free energy of adhesion
surface interfacial tension free energy of adhesion
Substance tension (mN/m) vs. water (mN/m) to water(mJ/m2)
CHCl
CCl

4. ΔGaSL = (ΔGaSL)LW + (ΔGaSL)AB (8)
For liquid on solid, contact angle follow the Young-Dupré
equation : γL(1 + cosθ) = -ΔGaSL (9)
The acid-base component of the free energy of adhesion is given by
(ΔGaSL)AB = -2(γS +γL-) ½ -2(γS –γL+) ½ (10)
(ΔGaSL)LW = -2(γS γL ) ½ (11)
γL(1 + cosθ) = 2(γS γL ) ½ + 2(γS +γL-) ½ + 2(γS -γL+) ½
(12) LW LW LW LW

5. apolar monopolar bipolar
γS = γL(1+cosθ)2/4
γS = γL (1+cosθ)2/4
= γL ( apolar liquid ) (1+cosθ)2/ (13) LW
γL(1 + cosθ) = 2(γS γL ) ½ + 2(γS +γL-) ½ + 2(γS –γL+) ½
γS = γS (γS +γS-) ½

6. γij : interfacial free energy between i and j γij = γij + γij
(15) LW AB
An important, practical restriction on the use of Eqs. (12) and
(13) Is the fact that the liquid must have a surface tension larger
than the critical surface tension of the solid.
The γS values for a large number of important polymer are in
the neighborhood of 40 mJ/m2. LW

7. Low surface energy finishes are important in many practical application.
γ,surface free energy of polymer
poly(tetrafluoroethylene), PTFE, Teflon γ= 21mJ/m2
polystyrene, PS, γ= 42mJ/m2
poly(methyl methacrylate), PMMA, γ= 39 to 43 mJ/m2
It is now established that the surface energy of constituent groups decreases in the order CH2 (36 dyn cm-1) > CH3 (30 dyn cm-1) > CF2 (23 dyn cm-1) > CF3 (15 dyn cm-1).

8. Amorphous materials exhibit lower surface energy values than crystalline counterparts.
As a general rule, amorphous, comb like polymers possessing a flexible linear backbone onto which side-chains with low intermolecular interactions are attached, exhibit low γ values.

9. Fluoropolymers and Silicones
poly(tetrafluoroethylene)
PTFE
The low intermolecular forces present in fluorinated polymers have been recognized to account for the relatively low surface free energy.
poly(dimethylsiloxane) PDMS
polyethylene PE

10. poly(perfluoroalkylacrylate) PFA
General Rules for Low Surface
Free Energy Polymers
As a general rule, amorphous, comb like polymers possessing a flexible linear backbone onto which side-chains with low intermolecular interactions are attached, exhibit low γ values.
poly(perfluoroalkylacrylate) PFA
Adv. Mater , 15, 647

11. The Influence of Intra- and Intermolecular
Interactions on Surface Free Energy
Poly(N-isopropylacrylamide) (PNIPAAm)
Hydrophilic
Hydrophobic
< LCST
> LCST
intermolecular hydrogen bonding
between the PNIPAAm main
chains and water molecules
intramolecular hydrogen bonding
between the C=O and N－H
higher surface free energy
lower water contact angles
low surface free energy
high contact angles for water
Angew. Chem. Int. Ed. 2004, 43, 357

12. The Influence of Intermolecular Hydrogen
Bonding on Surface Free Energy
ANA
6F acid
AAA
HQAT
J. Phys. Chem. B, 2001,105, 4145