Introduction to Surfactants & Interfacial Phenomena
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계면활성제(surfactant)란 ?
◆ 계면활성제(Surfactant)
: Surface Active Agents 의 약어로서 한 분자내에 서로 성질이
다른 2개의 그룹(친수부, 소수부)으로 이루어진 물질
Hydrophobic Group : Water Hating
Hydrophilic Group : Water Loving
Lyophobic Group : Solvent Hating
Lyophilic Group : Solvent Loving
Lipophilic Group : Oil Loving
Lipophobic Group : Oil Hating
Tail Group
Polar Head Group
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계면활성제의 종류 - Hydrophilic Group
Hydrophilic Group의 종류에 따라 분류한다
◆ Carboxylates (RCOOM)
Anionic
◆ Sulfates (OSO3M), Sulfonates (SO3M)
◆ Phosphates (OPO3M), Phosphonates (PO3M)
◆ Polyethylenegylcol (-CH2CH2O-)
Nonionic
◆ Polyhydric alcohol (Glycerol, Sorbitol, etc)
◆ Sugar Base (Glucose, Sucrose, etc)
◆ Aminoalcohol (Ethanolamine, etc))
◆ Amine Salts, Quaternary ammonium Salts
Cationic
◆ Pyridinium Salts
◆ Sulfonium Salts, Phosphonium Salts
◆ Amino Acids
Amphoteric
◆ Carboxybetaines
◆ Sulfobetaines
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계면활성제의 종류 - Hydrophobic Groups
◆ Straight-chain, long alkyl groups : CH3(CH2)n◆ Branched-chain, long alkyl groups :
CH3(CH2)nCH(CH2)mR
◆ Aromatic(unsaturated) groups :
◆ Polypropylene oxide :
-(CHCH2O)mCH3
CH3
◆ Polysiloxane groups :
-(Si-O)nCH3
◆ Long-chain perfluoroalkyl groups : CF3(CF2)n-
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Effects of Hydrophobic Group
◆ Length of the Hydrophobic Group
- 물에 대한 용해도의 저하, 유기용매에 대한 용해도의 증가
- 계면에서의 계면활성제의 분자가 조밀하게 packing
- 계면에서의 흡착이나 micelle를 형성하는 경향 증가
- 계면활성제의 M.P. 증가
◆ Branching, Unsaturation
- 물과 유기 용매에 대한 용해도의 증가
- 계면에서의 계면활성제의 분자가 looser packing(특히 cis type)
- Liquid crystal형성의 저해
- Oxidation의 유발, 생분해성의 감소
◆ Aromatic Nucleus
- Polar surface에 대한 흡착성의 증가
- 계면에서의 계면활성제의 분자가 looser packing
- Liquid crystal형성의 저해
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Raw Materials
Fats & Oils
Crude Oil, Natural Gas
Glycerin
Fatty Acid
Fatty
Amine
Soaps
Cationic
Surfactants
Fatty Acid
Methyl Ester
Alkanol
Amides
Fatty
Alcohols
Ethylene
Oxide
n-Paraffins
α-Olefins
i-Olefins
Oxoalcohols
n-Alcohol
SulfoEster
Alkyl(ether) sulfates
Alkyl(ether) phosphates
Ethylene
secAlcohols
Olefin
sulfonate
Nonionic
Surfactants
Alkylaryls
Alkane
sulfonate
Alkyl sulfates
Alkyl phosphates
Alkylbenzene sulfontes
Alkylphenol ethoxylates
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Applications of Surfactants
Consumer Products
Industrial Applications
◆ Detergents(Cleaning agents)
◆ Personal-Care Products( Shampoo etc)
◆ Cosmetics
◆ Foods
◆ Pharmaceuticals
◆ Agriculture
◆ Textile and fibers
◆ Chemical and plastic industry
◆ Paints and lacquers
◆ Leather and furs
◆ Photo industry
◆ Metal processing
◆ Adhesives
◆ Construction
◆ Fire fighting
◆ Mining and flotation
◆ Oil recovery
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Interfacial Phenomena
◆ Adsorption
◆ Micelles & Micellization (Self-Assembly Structure)
◆ Solubility
◆ Solubilisation
◆ (Macro)Emulsion & Microemulsion
◆ Wetting or Wettability
◆ Foaming & Defoaming
◆ Dispersing/aggregation of Solids
◆ Surfactant Interaction
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Adsorption and CMC (Critical Micelle Concentration)
◆ Major Characteristic of Surfactant
A higher conc. at surface/interface than bulk phase
( thermodynamics due to asymmetric molecular structure)
“ADSORPTION”
Non-polar phase (Air or Oil)
( liq/sol, gas/sol, gas/liq, liq/liq)
Surface/Interface
Polar phase (Water)
A Change the physical properties of Surface/interface
(esp. Reduce Surface Energy/Tension = Stable Surface)
“Surface Active”
Non-polar Liquid
Polar Solid
Polar Liquid
Non-Polar Solid
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Adsorption and CMC (Critical Micelle Concentration)
◆ Adsorption
& CMC
- No orientation
- Flat on surface
- No enough room to lie flat
- Begin to orient
Low Conc.
Very Low Conc.
- No change in adsorption
at surface/interface
- Micelle formation
- Saturated mono layer
- CMC
- Surface active properties
are at optimum
Monolayer at CMC
above CMC
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Adsorption and CMC (Critical Micelle Concentration)
◆ Why
do surfactants have a CMC ?
2 Opposite Forces
- Force 1 : Repulsive Force between Polar Head Groups
More Repulsive : Less tendency to form Micelles
- Force 2 : Attracting Force between Hydrophobic Groups
More Attractive : More tendency to form Micelles
- Force 1 > Force 2
Not Aggregate
- Force 1 < Force 2
Aggregate, Form Micelles
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Adsorption and CMC (Critical Micelle Concentration)
◆ The
effect of the various factors on the CMC (1)
1. Effective size of the hydrophilic group
- Size larger
CMC increase (due to Force 1 increase)
- Nonion Surfactant
Very small CMC (due to low polar charge)
- Amphoteric Surfactant
2 Charges are further apart
Higher CMC (due to effective polar size increase)
2. Effect of Counter ions
- Reduce Charge Density
CMC decrease (due to Force 1 decrease)
CMC (Ca2+ Salt) < CMC (Na+ Salt)
3. Addition of Electrolyte to Ionic Surfactant
- Reduce Charge Density
CMC decrease (due to Force 1 decrease)
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Adsorption and CMC (Critical Micelle Concentration)
◆ The
effect of the various factors on the CMC (2)
4. Effect of pH on Ionic Surfactant
- Higher pH
CMC increase (due to Force 1 increase / ionization increase)
5. Effect of the Chain Length of the Hydrophobic Group
- Longer Chain Length
CMC decrease (due to Force 2 increase)
6. Effect of Temperature on Nonionic Surfactant
- Higher Temperature
H-Bond (between EO & Water) decrease
Reduce Effective Size of the polar group
CMC decrease (due to Force 1 decrease)
7. Effect of Temperature on Ionic Surfactant
- Not apparent
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Adsorption and CMC (Critical Micelle Concentration)
Changes of various properties at CMC
Critical Micelle Concentration
Detergency
Density
Property
Surface tension
Equivalent conductivity
Interfacial tension
Concentration of Sodium Dodecyl Sulfate
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Adsorption and CMC (Critical Micelle Concentration)
Adsorption at Air/Liquid Interface
◆ Gibbs’ Adsorption Isotherm
Γ= －
1
dΥ
RT d lnC
Γ= amount of adsorbed surfactant(mole/cm2)
Υ= surface tension of the solution (dyne/cm)
cmc
Υ
Γ
C sat = cmc
logC
Concentration
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Adsorption and CMC (Critical Micelle Concentration)
Adsorption at Liquid/Liquid Interface
◆ Υ= Interfacial tension of the solution (dyne/cm)
◆ Adsorption occurs in the oil/water interface because of the
attraction of hydrophobic and/or hydrophilic groups.
◆ Emulsification (HLB number)
Oil
60
Υ
40
20
Water
0
Concentration
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Adsorption and CMC (Critical Micelle Concentration)
Adsorption at Solid/Liquid Interface
◆ Hydrophilic group-oriented adsorption
Water repellent treatment of textile, antirusting, flotation
◆ Hydrophobic group-oriented adsorption
Carbon black, organic pigments, polymer latex in aqueous solutions
◆ Dispersing effect(wetting)
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Surface tension & Interfacial tension
What is Surface Tension?
◆ Cohesive force works between molecules, attracting them each
other to form liquid and solid
◆ The larger cohesive force, higher surface tension
Atmosphere
Liquid
◆ Surface tension
Temp.(℃)
Υ(dynes/cm)
Water
25
72.0
Ag
900
1140
n-Octane
20
21.8
Benzene
25
28.22
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Surface tension & Interfacial tension
What is Interfacial Tension?
◆ Interfacial tension occurs because the molecules at the interface
have higher energy compared with the molecules within each phase.
◆ The larger cohesive force, higher interfacial tension
Liquid A
Liquid B
◆ ΥAB = ΥA + ΥB －2∑AB
where ∑AB is the attractive force between Liquid A and B
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Micellization
Structure and Shape
Israelachvili et al
(a) (normal)micelle
(b) reversed
Value of VH/lca0
Structure of Micelle
0 ∼1/3
Spherical in aqueous
1/3 ∼1/2
Cylindrical in aqueous
1/2 ∼1
＞1
(c) spherical
(d) cylindrical (rod-like)
Lamellar in aqueous
Reversed micelles
in nonpolar
VH : volume of hydrophobic group
in the micelle core
lc : the length of hydrophobic group
in the core
a0 : cross sectional area occupied
by the hydrophilic group
(e) hexagonal
(f) lamellar
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Micellization
Aggregation Numbers
◆ Aggregation number ( n=4/3(lc)3/VH) increase
- Length of hydrophobic group의 증가
- Hydrophilic group의 감소
- The binding of counter ions의 증가
Hydrophilic
Hydrophobic
Loosed, bulky
Long, thin
☞ Spherical
Small, Closed
Short, bulky
☞ Lamellar/Cylindrical
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Solubility
◆ Krafft Point (Ionic Surfactants)
◆ Cloud Point (Nononic Surfactants)
Concentration
- As temperature increase,
Crystalline
Solid
Micellar Solution
the surfactants become hydrophobic,
phase separation.
- Nonionic surfactants have ten times
the solubilizing ability of anionics.
Monomer Solution
Krafft
Point
Temperature
- Solubilization is remarkably large at
Cloud Point of nonionic surfactants
- Thermodynamically stable(cf;emulsion)
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Emulsion
What’s Emulsion?
A. Oil in Water (O/W)
Water : Continuous Phase
◆ Emulsion Factors
- Kind Emulsifiers
- Temperature
- Volume ratio of
both liquid phases
- The container wall
B. Water in Oil (W/O)
Oil : Continuous Phase
◆ Determination of the Type
of Emulsion
- Coloring Materials
- Electrical Conductivity
- Dilution
- Breaking of Emulsion
- Wetting of Container Wall
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Emulsion
Property of Emulsion
a) Size and distribution
- The type of emulsifier and emulsion method
- If the droplet is too small, coalescence occur(unstable)
b) Viscosity of Emulsion
- The fluidity of emulsion is important of stability.
- Affected by volume ratio of dispersed particle, type of emulsifier,
concentration,particle size.
c) Stability of Emulsion
- Stable emulsion : small size and narrow range distribution.
- Process of breaking : creaming, flocculation and coalescence
creaming
flocculation
flocculation
coalescence
oil phase
water phase
creaming
coalescence
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Emulsion
flocculation
coalescence
◆ In order to prevent creaming
- small size and narrow range distribution.
- density control(reduce difference)
◆ In order to prevent flocculation
- electrical repulsion(DLVO theory).
- steric hindrance
◆ In order to prevent coalescence
- strong absorbency is necessary.
- the adsorbed emulsifier molecules must have enough affinity to both liquid
- viscoelasticity(surface elasticity)
- use nonionic higher polymer emulsifier
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Emulsion
Selection of Emulsifiers
Most important to select the most stable emulsifiers for emulsion
◆ HLB(hydrophilic Lipophilic Balance)
- HLB number : Griffin
- the function of weight percent of the hydrophilic group of nonionic surfactants
- Low number : more lipophilic emulsifier
- High number : more hydrophilic emulsifier
◆ PIT(phase inversion temperature)
- W/O change to O/W or O/W change to W/O
◆ Required HLB
- When a specific oil is emulsified, the HLB number of the emulsifier which
makes the most stable emulsion
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Wetting
◆ Wetting : Solid/Gas Interface
θ
Water
Liquid/Solid Interface
A = σℓcos θ
σℓ = surface tension of liquid
θ is smaller, A is lager for the wettable
◆ Spreading Wetting(Ws)
θ
Mercury
◆ Immersional Wetting(Wi)
A = σs - σ I
A = wetting tension
σs = gas/solid interfacial tension
σi = liquid/solid interfacial tension
θ = contact angle
◆ Adhesional Wetting(Wa)
A＞0, therefore spreading at σs ＞ σ i
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Wetting
◆ Various Examples of Wetting
Spreading Wetting
Paint and Painting
Coating of plastics
Antifogging of glass
Draining
Rapid drying
Lubrication
Antistatics
Dust proofing
Soldering
Immersional Wetting
Adhesional Wetting
Dispersion and
coagulation
Adhesives
Chromatography
Migration of inks
Degradation of tablet
Demolding
Adsorption of
moisture by powder
Adhesion of bubbles
Wetting of textiles
in dyeing
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Wetting
◆ Surfactants : Unwettable Surface
Contact Angle θ 〉90o
Wettable Surface
θ〈 90o
- The hydrophobic groups of surfactants are absorbed on the surface
and their hydrophilic groups face the water
- The surfactants having the hydrophilic groups with the electric charge
opposite that of the surface are used and they adsorbed electrically on
the surface with their hydrophilic groups.
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Foaming and defoaming
Foaming
◆ Deinking agents(recycling paper), floatation of minerals, concrete, urethane etc.
◆ Alkyl chain of 12 to 14 carbon atoms is high foaming.
◆ Foam property depends on the chemical structure.
◆ Generally , better cleaning higher foaming.
◆ Nonionics is lower foaming but better cleaning.
- When ethyleneoxide unit is around 10, foaming is increased rapidly.
- When temperature is slightly higher than cp, most foam.
◆ The highest foaming occurs at above cmc.
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Foaming and defoaming
defoaming
Foam breaker
Foam lamellae
Foam Breakers
◆ Dropped or sprayed
◆ Low viscous and water-insoluble
- Higher fatty alcohol
- Fatty acid ester
- Phosphate ester
- Silicone oil
Foam Inhibitor
◆ Prevent foaming
◆ water-insoluble liquid and solid
- Metallic soap
- Fatty acid amide
- Higher fatty alcohol
- Propyleneoxide
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Foaming and Antifoaming(Defoaming)
1. Foaming
◆ Foam consist of thin liquid films with approximately plane parallel sides.
◆ Absolutely pure liquids do not produce foam.
◆ Foam is also not pronounced in mixtures of similar types of materials.
2. Foam 관련 용어
◆ Liquid/ Gas interface adsorbed films의 생성 여부
Foaming
Nonfoaming.
◆ Film elasticity
Persistent(metastable ) foams
Transient(unstable) foams
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Foaming and Antifoaming(Defoaming)
3. The Factors Promoting Foaming
◆ Low equilibrium surface tension
◆ Moderate rate of attaining equilibrium surface tension.
◆ Large surface concentration of surfactants
◆ High bulk viscosity
◆ Moderate surface viscosity.
◆ Electrical repulsion between the two sides of foam
4. The Factors of Foam
◆ Concentration
◆ Temp.
◆ Hardness of water
◆ Electrolytes
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Foaming and Antifoaming(Defoaming)
5. Efficiency As a Foaming Agents
◆ CMC 이하의 농도에서 foam height는 농도가 증가함에 따라 증가.
◆ CMC 부근 또는 약간 높은 농도에서 maximum foaming height
◆ Lower CMC를 갖는 surfactants 가 good foaming agents
◆ Neutral electrolytes increase foaming.
6. Effectiveness of foaming agent
◆ Low CMC, low surface tension ⇒ good foaming
◆ Branched chain surfactants ⇒ higher initial foam, less foam stability
◆ Increase of alkyl chain ⇒ chain cohesion 증가
Too short chain ⇒ insufficient cohesiveness
Too long chain ⇒ too much rigidity
◆ Highly branched chain ⇒ lower foam height
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Foaming and Antifoaming(Defoaming)
7. Low Foaming Surfactants
◆ Rapidly diffusing, reducing elasticity of surface film.
◆ Large, straight-chain ⇒ isomeric branched-chain.
◆ Terminal positioning ⇒ positioning the hydrophilic group in a central.
◆ Highly branched chain or second hydrophilic group ⇒ looser packed noncoherent film
◆ Highly branched or relatively short chain, second hydrophobic group.
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Foaming and Antifoaming(Defoaming)
8. Antifoaming
◆ By removing surface active materials from the bubble surface
⇒ Υ air/surf 》 Υ sol/surf
예) fine silica particles in silicone oil
◆ By replacing the foam film with an entirely different type of film.
1) Swamping with rapid diffusing noncohesive molecules of limited solubility.
예) Ethyl ether(17 dyne/cm), isoamyl alcohol(23 dyne/cm)
2) Replacing elastic surface with a brittle, close packed surface film.
예) Calcium salts of fatty acid
◆ By promoting drainage in the foam lamellae.
예) tributyl phosphate
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Dispersion
Emulsion And Dispersion
◆ Emulsion : the polarity of two phases is quite different in water and oil.
Dispersion : the polarity of two phases can be similar in medium and particles
◆ Emulsion : spherical shape
Dispersion : various shape
◆ Emulsion : creaming, flocculation and coalescence
Dispersion : settling, separation and slight flocculation
Free settling
Flocculent settling
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15. Detergency
15-1 Wetting Process
◆ Surfactants adsorbed on the surface(solid or oil)
15-2 Soil-Removing Process
◆ Removal of liquid and solid soil
- Liquid soil : Rolling-up model
- Solid soil : Electrostatic interaction
- Anionic surfactants increase the negative charge : good soil removal.
- High alkaline increase cleaning effect(negative zeta-potential )
- Maximum cleaning power is obtained at optimum concentration of salts.
- Nonionic surfactants is excellent cleaning agent oil soil.
◆ Soil redeposition
- The method to prevent redeposition is same as stabilization of dispersion
and emulsion.
- Polymer(CMC, PEG etc)
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17. Synergistic Effects
◆ When formulating emulsion and dispersion etc, desired effect can be achieved to
employing combinations of surfactants.
◆ Homo-synergism : similar structure and same ionic surfactants.
Hetero-synergism : combination of surfactants having different properties.
◆ β parameter
If β is negative, attractive force
If β is positive, repulsive force
S
1
synergism
antagonism(negative synergism)
2
A
Υ
Log C
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17. Synergistic Effects
◆ Factors on Synergism
- Chemical structure
- Ionic character
- Mixing ratio(mole fraction)
◆ Synergistic effects
- Formation complex : anionic and amphoteric, anionic and cationic,
cationic and amphoteric, ionic salts.
- Week interaction : by mixing more than two kinds of nonionic in emulsification.
Mixing anionic with fatty alcohol.
Stable emulsion
Stable dispersion
Stable forming
Good detergency etc
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Future trends of Surfactants
◆ Raw materials
Renewable Resources
- Sugar base(APG, Glucamide)
- Amino acid base
Petrochemicals Materials
- LAS, Nonylphenol
- Biodegradability
- Toxicity
- Eco-Hormone
- Resources
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Future trends of Surfactants
◆ High Performance
- 고효능화
- Compact 화
- 자원의 절약
◆ Multi- Function화
기능A
Surfactants
기능B
Chelating
Polymer
Multi-Function화
Chelating Surfactants
Polymerizable Surfactants
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Cutting Oil
-
◆ Soluble Cutting Oil
Oil
- Lubrication
- Wetting
- Emulsifier
Surfactants
-
Water
- Cooling
- Anionic type : Sufonates, Carboxylates(Soap)
◆ Surfactants
- Nonionic type : Alkylglycolethers, Specials
- Counter : Na, NH3, Alkanolamines
- Solubilizers : PEG, Butyl alcohol etc.
◆ Additives
- Anti-forming agents
- Anti-rusting agents
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Cutting Oil
Performance
◆ Requirements
Environment
- Efficient Lubrication
- Odor
- Cooling Efficiency
- Irritation
- Fire-Resistance
- Biodegradability
Soluble
- Cutting Oil
(Emulsion type)
- Lubrication
- Cooling
- Non-aqueous
Cutting Oil
- Lubrication
◆ Classification
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