Title: Surface energy study
1Surface energy study
?S surface free energy of solid ?L surface
free energy of liquid ?SL interfacial free
energy between solid and liquid ? solid/liquid
contact angle Youngs equation ?SL ?S - ?L
cos? (1) ?SL ?S
?L - 2(?S ?L) ½ (2) from (1) (2)
?S ?L(1cos?)2/4
(3)
2Fowkes first suggest that surface tension could
resolved into component due to dispersion force,
the induction and dipole-dipole forces, and
hydrogen bonding
3Hydrogen bonding
We may compare the surface tension data of CHCl3
and CCl4 and interfacial tension vs. water and
free energy of adhesion to water. -?Gaij ?i
?j - ?ij (7) -?Gaij free energy of
adhesion
surface
interfacial tension free energy of
adhesion Substance tension (mN/m)
vs. water (mN/m) to water(mJ/m2)
CHCl3 27.13
31.6 -68.3
CCl4 26.95
45.0
-54.7
4- ?GaSL (?GaSL)LW (?GaSL)AB (8)
- For liquid on solid, contact angle follow the
Young-Dupré - equation ?L(1 cos?) -?GaSL (9)
- The acid-base component of the free energy of
adhesion is given by - (?GaSL)AB -2(?S ?L-) ½ -2(?S ?L) ½ (10)
- (?GaSL)LW -2(?S ?L ) ½ (11)
- ?L(1 cos?) 2(?S ?L ) ½ 2(?S
?L-) ½ 2(?S -?L) ½ - (12)
LW
LW
LW
LW
5(No Transcript)
6An 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 ?S
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.
?,surface free energy of polymer poly(tetrafluoroe
thylene), PTFE, Teflon ? 21mJ/m2 polystyrene,
PS, ? 42mJ/m2 poly(methyl methacrylate), PMMA,
? 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) gt CH3 (30 dyn cm-1) gt CF2 (23 dyn cm-1)
gt 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 ? values.
9Fluoropolymers and Silicones
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
10General 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 ? values.
poly(perfluoroalkylacrylate) PFA
Adv. Mater. 2003, 15, 647
11The Influence of Intra- and Intermolecular
Interactions on Surface Free Energy
Poly(N-isopropylacrylamide) (PNIPAAm)
Hydrophilic
Hydrophobic
lt LCST
gt LCST
intramolecular hydrogen bonding between the CO
and N-H
intermolecular hydrogen bonding between the
PNIPAAm main chains and water molecules
low surface free energy high contact angles for
water
higher surface free energy lower water contact
angles
Angew. Chem. Int. Ed. 2004, 43, 357
12The Influence of Intermolecular Hydrogen Bonding
on Surface Free Energy
ANA
6F acid
AAA
HQAT
J. Phys. Chem. B, 2001,105, 4145