1. From Surfactant to Foam
… a short journey across
colloid & interfacial chemistry
Prof. Cosima Stubenrauch
Institut für Physikalische Chemie
Universität Stuttgart
3. Photograph by Prof. J. Cilliers, Imperial College
3
Polyederschaum - „dry foam“
gas volume > 74%
5
air
Kugelschaum - „wet foam“
air
water
air
H2O
Liquid Foams
4. Foam – Film – Surface – Surfactant
air
H2O
air
h
air
H2O
4
Polyederschaum - „dry foam“
gas volume > 74%
5
air
7. surface tension of surfactant solutions
s = 30 – 40 mN m-1 = 30 – 40 mJ m-2 = 0.03 – 0.04 J m-2
ln csurfactant
s
/
mN
m
-1
72
30
low adsorption
= high s
high adsorption
= low s
7
Surfactants & Surfaces
Gibbs adsorption isotherm !
8. surface elasticity of surfactant solution
e = 10 – 100 mN m-1 = 10 – 100 mJ m-2 = 0.01 – 0.1 J m-2
)
ln
d(
d
A
s
e
Gibbs-Marangoni-Effect
Surfactants decrease the surface tension of water
and render the water-air surface elastic!
low adsorption
= high s
high adsorption
= low s
8
Surfactants & Surfaces
Lecture I.3
9. Foam – Film – Surface – Surfactant
air
h
air
H2O
air
H2O
9
low surface tension,
high surface elasticity
Polyederschaum - „dry foam“
gas volume > 74%
5
air
Relation between
surfactant structure and
surface elasticity?
10. 10
Isenberg, The Science of Soap Films and Soap Bubbles, Dover Publications, New York, 1992
Surfaces & Films
air
H2O
5 – 30 nm
50 – 120 nm
130 nm
250 nm
480 nm
11. ~1.5 mm
surfactant solution
air
Pg Pl
Mysels, K. J., Jones, M.N., Discuss. Faraday Soc. 1966, 42, 42; Exerowa, D., Scheludko, A., C. R.
Acad. Bulg. Sci. 1971, 24, 47; Stubenrauch, C., Klitzing, R. v., J. Phys.: Condens. Matter 2003, 15, R1197
10
cm
11
Surfaces & Films
14. 10 nm < h < 100 nm
Common Black Film, CBF
h < 10 nm
Newton Black Film, NBF
14
h H2O
electrostatic stabilisation
air
air
h
steric stabilisation
air
air
strength of repulsive interactions = film thickness (film stability)
– control via choice of surfactant and surfactant concentration –
Surfaces & Films Lecture I.2
15. Foam – Film – Surface – Surfactant
air
h
air
H2O
air
H2O
15
low surface tension,
high surface elasticity
strong repulsive surface interactions
Polyederschaum - „dry foam“
gas volume > 74%
5
air
Relation between
surfactant structure and
surface elasticity?
17. 17
Films & Foams
time
Foam Decay
drainage – gravitation
„Stabilisation“
highly viscous liquid
decreasing water content
coalescence – film rupture stable films
destruction of bubbles
Ostwald ripening – gas transport low gas solubility
disappearance of small bubbles
18. Films & Foams
18
p1
2 balloons at steel tube
p2
p1 < p2 as p ~ 1/radius
(Dp = 2g/r = Laplace pressure)
gas transport
2 gas bubbles in solution
gas transport
p1 p2
gas bubbles in foam
slowing-down of Ostwald ripening
• densely packed surfactant layer – permeability!
• low polydispersity of bubble size – millifluidics !
• low gas solubility (N2 << CO2) – beer foam !
20. Films & Foams
20
p1
2 balloons at steel tube
p2
p1 < p2 as p ~ 1/radius
(Dp = 2g/r = Laplace pressure)
gas transport
2 gas bubbles in solution
gas transport
p1 p2
preventing Ostwald ripening: adding traces of SF6
driving force: chemical potential
µ(SF6)droplet 1 = µ(SF6)droplet 2
21. Foam – Film – Surface – Surfactant
air
h
air
H2O
air
H2O
21
low surface tension,
high surface elasticity
strong repulsive surface interactions
slowing-down drainage, coalescence,
and Ostwald ripening
MANY open questions !!!
Control of Foam Stability
type and concentration of surfactant,
surfactant mixtures, additives....
Polyederschaum - „dry foam“
5
air
22. How long does it take to gene-
rate a fixed amount of foam?
22
How much foam can be gene-
rated within a given time?
FoamScan, TECLIS, France;
http://www.teclis.eu
How To Study Foams?
23. 0
Q / ml min
-1
23
t = Vfoam Q-1
drainage
long time
short time
Generation of fixed amount of foam!
Q / ml min
-1
t
s
generation of fixed
amount of foam
How To Study Foams?
24. 24
time
Foam Decay
drainage – gravitation
„Stabilisation“
highly viscous liquid
decreasing water content
coalescence – film rupture stable films
destruction of bubbles
coarsening – gas transport low gas solubility
disappearance of small bubbles
How To Study Foams?
27. 27
Foam Properties depend on Foam Structure…..
• initial liquid fraction
• average bubble size
• bubble size distribution
Protocol for Studying
Aqueous Foams Stabilized
by Surfactant Mixtures*
* Paper Award of the American Cleaning Institute 2013
J. Boos, W. Drenckhan, C. Stubenrauch, J. Surf. Det., 2013, 16, 1-12
Foam Properties depend on Formulation…..
• amount of surfactant
• type of surfactant
• additives (salt, co-surfactant, thickener….)
How To Study Foams?
Lecture I.4
Lecture I.4
29. 29
Foam Films and Foams in Art
Amor with Soap Bubble, Rembrandt 1634
30. 30
Soap Opera, Tim Durham - http://timdurham.ie/1%20Projects/25
Foam Films and Foams in Art
31. Name
Beijing National
Aquatics Center
Capacity 17,000 people
Built 2004–2007
Opened 2008
built for swimming competition at the Olympic Games 2008 in Beijing
optimum foam structure based on
computer simulations of Weaire
and Phelan, 1993, Trinity
College, Ireland
31
http://en.wikipedia.org/wiki/Beijing_National_Aquatics_Centre
Foam Films and Foams in Art
32.
33. 33
References
• D. Weaire, S. Hutzler, The Physics of Foams, Clarendon Press,
Oxford, 1999
• C. Isenberg, The Science of Soap Films and Soap Bubbles, Dover
Publications, New York, 1992
• Emulsions, Foams, and Suspensions - Fundamentals and
Applications, L.L. Schramm, Wiley-VCH, Weinheim, 2005
