Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil...
Transcript of Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil...
![Page 1: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/1.jpg)
B. Foam films – basic properties and methods for investigation.
A. Chemistry of foam stabilizers.
C. Antifoams.
Foam films:Properties and Stability
![Page 2: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/2.jpg)
A. Chemistry of foam stabilizers
CONTENTS
1. Nonionic, ionic, and amphoteric surfactants.
2. Polymeric surfactants.
3. Particles as foam stabilizers.
Aim of presentation
Relation between surfactant chemical structure and mode of foam stabilization
![Page 3: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/3.jpg)
Low-molecular mass surfactants1. Nonionic surfactantsAlkylpolyoxyethylenes
CnEOm
TweensSpans
![Page 4: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/4.jpg)
2. Ionic surfactants
n=12 ⇒ sodium dodecyl sulfate, SDS
(a) Anionic
Diffuse electric
layer
(b) Cationic
n=12 ⇒ dodecyl trimethyl ammonium chloride, DTAC
![Page 5: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/5.jpg)
3. Amphoteric surfactants
(b) Betaines
(a) Natural soaps (alkylcarboxylates), Lipids
![Page 6: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/6.jpg)
Comparisonof the low-molecular mass surfactants
Surfactant mixtures are usually used in applications(main surfactant + cosurfactants)
*Adsorption, surface tension, CMC, micelle size and shape, foaminess and foam stability
Sensitivity* Nonionic Ionic Amphoteric
Electrolytes NO YES Depends on pH
Temperature YES NO NO
pH NO NO YES
![Page 7: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/7.jpg)
Polymeric surfactants1. Synthetic polymers(a) Homopolymers
Polyvinyl alcohol, PVA
Modified polysacharides
(b) Block-copolymers
Synperonics, EOnPOmEOn
![Page 8: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/8.jpg)
2. Natural polymers (proteins)(b) Fibrilar
β-caseinκ-casein
(a) Globular
Bovine serum albumin, BSAβ-lactoglobulin, BLG
3. Solid particles(a) Mineral (b) Polymeric
SiO2Ore particles Latex particles
![Page 9: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/9.jpg)
Modes of foam stabilizationby polymeric surfactants
Usually: combination of steric + electrostatic stabilization
Synthetic polymers Natural polymers
Polymer-surfactant mixtures are often used!
![Page 10: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/10.jpg)
Foam film stabilization by solid particles
Relatively thick foam films.The foams could be very stable against coarsening!
Difficult to produce:Slow adsorption (D = kT/6πηR)No Marangoni effect (EG = -(dσ/dlnΓ) ≈ ΓkT = kT/A0)Strong capillary attraction between particles⇒ Creation of “weak” spots (free of particles) in the films!
Mixture of particles + surfactants(ice-cream, whipped cream, chocolate mousse, … )
![Page 11: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/11.jpg)
B. Foam films
CONTENTS
1. Properties of equilibrium foam films.
2. Rate of thinning of foam films.
3. Methods for studying foam films.
4. Illustrative examples
Aims of presentation:
Information gained by studying foam films.Illustration of differences between surfactants.
![Page 12: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/12.jpg)
1. Basic properties of equilibrium foam films.
1. Equilibrium film thickness
( )EQ A L Ch P P PΠ = − =Pressure balance
σ = σ θcos ;f ( ) ( )σ = σ + / 2f h f h
2. Contact angle film-meniscus Film tension
( ) ( )2 cos 1f h = σ θ −
Interaction energy
( ) ( )h
f h h dh∞
= Π∫
![Page 13: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/13.jpg)
Transition zone film-meniscusOpen questions from the thermodynamic approach:• Do we have a sharp kink in the shape?• What does compensate the vertical projection of σ?
( ) ( )−
⎛ ⎞Π + − = −σ +⎜ ⎟
⎝ ⎠14243 1 2
1 1
C
L A
P
h P PR R
Local stress balanceτ = σ θsin
Idealized profile Real profile
![Page 14: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/14.jpg)
Rate of thinning of foam films Driving force= − > 0C A LP P P
Limitations of Reynolds equation:
Tangentially immobile surfacesPlane-parallel filmsThe real films thin faster!
Reynolds equation for film thinning
( )− Π= − =
η
3
Re 2
23CP hdhV
dt R
rV
Vz
∂⎛ ⎞τ = −µ⎜ ⎟∂⎝ ⎠
S r∂σ⎛ ⎞τ = −⎜ ⎟∂⎝ ⎠
Role of Marangoni effect
![Page 15: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/15.jpg)
Rupture of foam films
“Barrier” mode of rupture “Under-barrier”
mode of rupture
![Page 16: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/16.jpg)
Methods for studying foam films
1. Large foam films suspended on a glass frame
White light – beautiful colors (light interference)
Monochromatic light – dark and bright stripes (film thickness)
![Page 17: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/17.jpg)
ExamplehD = k Ca2/3
Ca = (µV/σ)
Measuredh (time), h (position)arcsin
2MIN
MAX MIN
I Ih kn I I⎛ ⎞−λ
= π +⎜ ⎟⎜ ⎟π −⎝ ⎠
Film thickness
λ - light wavelengthn - refractive index of solutionk - order of interference
![Page 18: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/18.jpg)
2. Microscopic foam films in a capillary cell
Measuredh(t), hEQ
Contact angle, θ
Film thickness vs time
![Page 19: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/19.jpg)
3. Porous plate method
Measured:• Equilibrium thickness, hEQ(PC)• Disjoining pressure, Π(h)• Critical pressure for film rupture, ΠCR
Disjoining pressure isotherm
PC = (PA – PL) = Π(hEQ)
![Page 20: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/20.jpg)
Illustrative examples
Anionic surfactant, SDS
Speed: ×1
Polymeric surfactant, PVA
Speed: ×4
Protein,Na caseinate
Speed: ×8
hEQ ≈ 10 nmτDR ≈ 60 sec
hEQ ≈ 120 nmτDR ≈ 300 sec
hEQ ≈ 30 nmτDR ≈ 600 sec
![Page 21: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/21.jpg)
No surfactantSpeed: 1/4
Very rapid film thinningFilm rupture at large thickness
(no Marangoni effect)
![Page 22: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/22.jpg)
Why and where foam control is needed?
TECHNOLOGY
• Pulp and paper production
• Oil industry (non-aqueous foams)
• Fermentation
• Textile dying
• Powders for washing machines
• Paints
• Drugs
CONSUMER PRODUCTS
C. Antifoamsantifoam effect of hydrophobic particles and oils
What is “antifoam effect”?
![Page 23: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/23.jpg)
CONTENTS
1. Composition of typical antifoams.
2. Mechanisms of foam destruction.
3. Examples of antifoam actions.
Aims of presentation:
Mechanisms of foam destruction by antifoams.Illustrative examples.
![Page 24: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/24.jpg)
Composition of Typical Antifoams
2. Oil
Silicone oils (PDMS)Hydrocarbons (mineral oil, aliphatic oils)
Silica particles Emulsified oil
100 nm 30 µm
Silica (SiO2)Polymeric particles
3. CompoundOil + particles
Compoundglobule
30 µm
1. Hydrophobic solid particles
![Page 25: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/25.jpg)
Time, min0 1 2 3 4 5
Foam
vol
ume,
VF,
mL
0
50
100
150
200No antifoam
Silicone oil
Silicone oil+ silica
10 mM AOT
Fast Antifoams• Foam lifetime ~ seconds• Foam completely destroyed
Slow Antifoams• Foam halftime ~ minutes• Residual foam
Mechanisms of antifoam action:Fast and Slow antifoams
![Page 26: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/26.jpg)
Characteristic size- and time-scales in foam
Size scales:• Foam films
eq. thickness ∼ 15 nm• Plateau borders (PB)
section ∼ 100 to 1 µm• Nodes
section ∼ 100 to 1 µm
2RF
h
Foam film
RB
cross-sectionof PB
Plateau bordernode
RPB
Time scales:Foam filmsto 1 µm for several secondsPlateau Borders at RB = 1 mm τDR ≈ 80 s at RB = 300 µm τDR ≈ 800 s
![Page 27: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/27.jpg)
Film rupture by solid particles:bridging-dewetting mechanism
Key factors:(1) Contact angle(2) Particle size and shape
90> oθ 45θ > o
![Page 28: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/28.jpg)
Bridging
StretchingDrop entry
Air
Water
Air
Key factors: (1) Interfacial tensions(2) Oil rheology
Foam film rupture
Film rupture by oil-solid compounds:bridging-stretching mechanism
![Page 29: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/29.jpg)
Film rupture after oil spreading
Key factors: (1) Rate of oil spreading(2) Thickness and structure of spread layer
Spreading coefficient
(b) Rupture of thin foam films(surfactant displacement by oil)
AW OW OAS = σ − σ − σ
(a) Rupture of thick foam films(suppressed Marangoni effect)
Modes of film ruptureby spread oil
![Page 30: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/30.jpg)
The fast antifoams rupture the films almost immediately after film formation at thickness ~ 1 µm
Microscopic film -initial stage of film rupture
100µm
Large foam film suspended on glass frame - expanding hole
(high speed camera, 500 fps)
2 cm
Optical observation of film rupture(fast antifoams)
![Page 31: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/31.jpg)
Optical observation of film rupture(fast antifoams)
Large foam filmsuspended on glass frame(high speed camera, 500 fps)
![Page 32: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/32.jpg)
Slow antifoams: Oils drops trapped in Plateau channels
Slow Antifoams – the oil drops:• Escape from the foam films without rupturing them• Accumulate in the Plateau channels of the foam• Break the foam films after entry in the Plateau channel
Oil drops
![Page 33: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/33.jpg)
Slow antifoams -Entry in the Plateau borders
Key factors: (1) Critical pressure for drop entry (entry barrier) (2) Drop size
![Page 34: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/34.jpg)
Foam film rupture by slow antifoam (silicone oil)
The spread oil ruptures the thin foam filmsprobably by surfactant displacement
![Page 35: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/35.jpg)
Enhanced foam stability by using Cosurfactants
Time, min0 20 40 60 80 100
Foam
hei
ght,
cm
0
5
10
15
20
25
Betaine
Betaine+SDP3S
SDP3S
0.1 wt % silicone oil
![Page 36: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/36.jpg)
Classification:Types of antifoam
and mechanisms of antifoam action
Antifoam composition
Type of action
Mode of foam destruction
Schematic presentation
Solid particles Slow (fast) Bridging-dewetting
Oils Slow Spreading
Oil-solid Fast Bridging-stretching
Bridging-dewetting
![Page 37: Foam films: Properties and Stabilityfoams/PRESENTATIONS/Thursday12/Thu… · Film rupture after oil spreading Key factors: (1) Rate of oil spreading (2) Thickness and structure of](https://reader034.fdocuments.in/reader034/viewer/2022042213/5eb7546ab73e2b700348cd72/html5/thumbnails/37.jpg)
SINCERE THANKS
Dr. S. TcholakovaHelp in preparation of the presentation.
Miss M. ParaskovaPreparation of some of the figures.
Other colleaguesThe Laboratory of Chemical Physics & EngineeringFaculty of Chemistry, University of Sofia, Sofia, Bulgaria