Lamellar Gel Network (LGN)
Based Formulations
Deckner Consulting Services
LLC
Why Are They Important?
• Most oil in water skin care emulsions sold globally are based on LGNs
stabilized with polymers
• Most hair conditioners sold globally are based on LGNs
• The peroxide phase of many two part hair dye formulations are LGN
based
• Many cream depilatories and hair relaxers are LGN based
Lamellar Gel Networks (LGN)
Advantages
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Low and high pH stable systems are possible
Can formulate PH, salt, and peroxide stable systems
Can suspend and stabilize powders or pigments
Have good moisturizing properties
Can prolong the release of oil-soluble actives
Can stabilize some types of actives
Very stable (if phase transition temperature is >50C)
Can make water proof/wash resistant products
Very low in skin irritation potential
Very cost effective
Disadvantages
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Systems can be very processing sensitive
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Need high levels of low HLB surfactant (typically 3-10%) which can negatively affect skin feel
What are LGNs?
Combinations of low and high HLB crystalline surfactants that can swell
and thicken water. The gel network is stabilized by lamellar bilayers of
surfactant which bind water. These systems have viscoelastic
properties and shear thin when applied to skin.
• A lamellar gel network can be defined as a network formed by bilayer sheets where the alkyl chains in the bi-layers are essentially in
a frozen non-melted state. This type of lamellar phase is also called
alpha phase or alpha gel
B
D
A
A
C
G. M. Eccelston, Multiple-phase oil-in-water emulsions, J.
Soc. Comet. Cbem., 41, 1-22 (January/February 1990)
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A-bound water phase
B-bulk water phase
C-oil phase
D-crystal hydrates
C
SEM of an LGN
Structure of a O/W emulsion with non-swollen co-emulsifier residues
b = gel network c, d = oil droplet
Model Fatty Alcohol/High HLB Surfactant LGN
D spacing
> 200Å
Low HLB Crystalline Surfactant
The purpose of the low HLB crystalline surfactant is to create structure and thicken
• Melting point typically should be >50C
• Fatty alcohols are the most efficient at thickening
• It is very difficult to swell fatty alcohols longer than C18-20 without using a low HLB
cosurfactant which is more polar than fatty alcohol or using high shear to reduce the
particle size
• Cetyl, Stearyl alcohols, Eicosanol, Behenyl alcohol, Glyceryl Stearate, and Sorbitan
Stearate are the most commonly used
• C16-22 saturated derivatives work the best
• Glyceryl Stearate and Sorbitan Monostearate are easier to swell than fatty alcohols
and can be used to reduce the amount of high HLB surfactant needed
High HLB Crystalline Surfactant
The purpose of the high HLB crystalline surfactant is to swell the low HLB
crystalline surfactant to promote lamellar bilayer formation
• Can be nonionic, anionic, or cationic
• Generally C16-22 derivatives work the best
• High HLB surfactant should be water soluble or dispersible
Importance of Surfactant Geometry
The ability to form a lamellar phase depends on the geometry of the high HLB and low HLB
surfactant used
Preferred
A High HLB Surfactant is
Needed to Form LGNs With Fatty Alcohol
FA
Fatty Alcohol Crystal
FA + H2O
Hydrated Fatty Alcohol Crystal
FA + High HLB surfactant+H2O
Lamellar Gel Network
LGN Formation
Phase transition temperature
(PTT)
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LGN
Surfactants penetrate into FA crystals and the repulsion between ionic polar head increases
the distance between lamellar bilayers, so more water can be introduced in between bilayers.
Lamellar phases spontaneously form in water
Tc = Hydrocarbon chain melting temperature = PTT (phase transition temperature)
α- Crystalline gel = Lamellar gel phases (gel network)
G. M. Eccelston, Multiple-phase oil-in-water emulsions, J. Soc. Comet. Cbem., 41, 1-22 (January/February 1990)
Viscosity of Gel Network is Impacted by High HLB Surfactant
Concentration
% High HLB surfactant /% of low HLB + % high HLB surfactant
β,γ
α-FA melting
endothermic
Fatty Alcohol Crystalline Hydrate phase and Gel Network Phase
Are Impacted by the Ratio of High HLB Surfactant Plus Low HLB
Surfactant
FA + H2O
α
CS + H2O
CS 10
CS 15
CS 20
CS25
CS 30
CS 35
CS 45
Gel Network melting
30
40
50
60 70
80
Temperature (ºC)
• Fatty alcohol crystalline hydrate endothermic peak disappears at CS > 25%
• Fatty alcohol crystalline hydrate melts at 14
~54ºC, while gel networks melt at ~72ºC
Surfactant Ratio Impacts The Amount of Hydrated Fatty Alcohol
Crystalline Phase and Gel Network Phase (Polarized Microscopy
Observation)
CS15
10
CS25
15
20
CS35
25
35
30
CS in mixed emulsifier (wt%)
CS45
40
45
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When surfactant ratio increases, fatty alcohol crystalline hydrates reduce in number, and
then disappear at CS> 25%.
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Processing can also have a big impact on the gel network structure
Always use Combinations of Fatty Alcohols (If using
Alone as A Low HLB Surfactant )
• 3 Crystal modifications of n-higher alcohol exist
• α-Form FA crystal is stable
16 FA crystal
• 40 wt% Stearyl alcohol in total alcohol has maximum α-form
Emulsion Made Using Cetrimonium Bromide and Cetyl Alcohol
Cetyl peak
LGN peak
G. M. Eccelston, Multiple-phase oil-in-water emulsions, J. Soc. Comet. Cbem., 41, 1-22 (January/February 1990)
LGN Characterization Methods
• Temperature at which the LGN gets noticeably thicker. This is similar to the
phase transition temperature from a liquid crystal to solid crystalline state.
• Electrical conductivity drops at the phase transition temperature
• Microscopy with and without polarizers
• Brookfield viscosity
• Rheometer in a constant shear mode with a temperature ramp from 10-60C
• Differential Scanning Calorimeter, can see fatty alcohol hydrate and gel phase
peaks
• Ultra centrifugation (75K cps overnight)
• X ray diffraction (can measure distance between bilayers)
Phase Transition From Lamellar Liquid Crystalline Phase to LGN Phase
Occurs as the Temperature is Reduced (conductivity measurement)
BO1 Conductivity Change During Making
500
phase
transition
lamellar liquid
crystalline phase
300
lamellar gel phase
200
lamellar gel phase
Conductivity (mS/m)
400
PTT =
72-67 ºC
100
0
85
80
75
70
65
60
Temperature (℃）
55
50
19
Ultra Centrifugation to Measure Bound Water
top layer
= hydrated fatty alcohol
middle layer = gel network
bottom layer = bulk water
Free Water for BTMAC Model System
Centrifuaged@75600g Overnight
The trend observed for “free water” is
consistent with the yield stress results.
Free Water (wt%)
60
50
40
30
20
10
0
0
10
20
30
BTMAC wt%
40
50
Factors Affecting LGN Viscosity
Concentrations of low and high HLB surfactant
Ratio of high to low plus high HLB surfactant
Amount of water and solvent in the formulation
Chain length of low and high HLB surfactants
The type and amount of electrolyte
High polarity oils
The type and amount of fragrance (especially those with a ClogP <2)
The amount and type of solvent preservatives (Benzyl alcohol, Phenoxyethanol, Ethylhexyl
Glycerin)
• Branched/unsaturated fatty acids, alcohols, mono/diglycerides
• Presence of polymers (soluble and swellable)
• Type of processing (high vs low shear), when shear is applied, cooling rate
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LGNs Formed Using Nonionic Ethoxylated High HLB Surfactants Are More
Processing Sensitive (Rapid Cooling)
Ethylene oxide chains progressively hydrate more on cooling
Impact of Perfume on LGN Viscosity
Model Formulation
Surfactant
1.5% (100% active)
Sorbitol
35.0 (70% active)
Cetyl alcohol
3.0%
Stearyl alcohol
3.0%
Water
92.0%
Fragrance
0-2%
% Perfume
0
.5
1.0
2.0
Viscosity (Brookfield [email protected] rpms)
34
20
15
11
Impact of Perfume on LGN Viscosity
Solvent preservatives like Benzyl alcohol, Phenoxyethanol, and Ethylhexyl Glycerin have a similar impact
Impact of Electrolyte on LGNs
• Electrolytes cause a loss in electrostatic repulsion when using charged surfactants
causing a reduction in bound water
• Electrolytes can cause a dehydration of the hydrophilic head-groups of ethoxylated
non-ionic surfactants resulting in a loss of solubility
Influence of NaCl On Lamellar Spacing
Cetrimide/fatty alcohol
G. M. Eccelston, Multiple-phase oil-in-water emulsions, J. Soc. Comet. Cbem., 41, 1-22 (January/February 1990).
Impact of High HLB Surfactant Chain Length on Viscosity
A (C12)
B (C12/14)
C (C14)
D (C16/18)
Viscosity*
Phase Transition Temperature
19
24
25
29
63C
64C
66C
69C
*Brookfield viscosity ([email protected] rpms)
Impact of Shear Processing on LGN Viscosity
Low shear
High shear (Ultra Turrax)
Lamellar bound water
Lamellar bound water
31.2%
8.2%
H Junginer, The ratio of Interlamellarly fixed water to bulk water in O/W emulsions
Impact of Increasing Shear Processing on LGN Viscosity (RheometerConstant Shear, Increasing Temperature-Above PTT)
Batches made with
different shear
above PTT then
switched to prop
mixing
Recommended Low HLB Crystalline Surfactants
Fatty Alcohols
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Cetyl, Stearyl, Eicosanol, or Behenyl alcohols
Sorbitan Esters
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Sorbitan Stearate, Behenate
Glyceryl Mono Esters
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Glyceryl mono/Distearate (40-60% mono)
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Glyceryl monostearate, Palmitate, or Laurate (90% mono)
Glyceryl Stearyl ether
Polyglycerol Esters
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Triglycerol Distearate
Recommended Low HLB Crystalline Surfactants
Glucose Esters
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Methyl Glucose Sesquistearate
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Polyglycerol-3 Methyl Glucose Distearate
Sucrose Esters (high in di ester)
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Sucrose Dipalmitate, Distearate
Ethoxylated Fatty Alcohols
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Steareth-2
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Beheneth-5
Recommended High HLB Crystalline Surfactants
Anionic
• Sodium Cetearyl Sulfate
• Sodium Stearoyl Lactylate
• Sodium Stearoyl Sarcosinate
• Sodium Stearoyl Glutamide
• Sodium Methyl Stearyl Taurate
Cationic
• Distearyldimethyl ammonium chloride
• Dicetyldimethyl ammonium chloride
• Behenyltrimethyl ammonium chloride
• Steapyrium chloride
Recommended High HLB Nonionic Crystalline Surfactants
Ethoxylated fatty alcohols
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Steareth-20 , Steareth-21
Ethoxylated fatty acids
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PEG 40 Stearate
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PEG 100 Stearate
Polysorbates
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Polysorbate 60 (PEG 20 Sorbitan Monostearate)
Polyglyceryl esters
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Decaglyceryl Monostearate
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Triglycerol Stearate
Sucrose Esters
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Sucrose Cocoate, Palmitate, Stearate (>70% mono ester)
Glucosides
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Cetearyl Glucoside
Recommended Self Emulsifying LGN Systems
Gel network bases are mixtures of low and high HLB crystalline surfactants
(~80/20) that disperse in water when added hot and form LGNs when
cooled
• Cetearyl alcohol, Cetearyl Glucoside
• Behenyl Alcohol, Glyceryl Monostearate, Lecithin, Soybean Sterols
• Polyglyceryl-3 Methylglucose Distearate
• Cetearyl alcohol, Dicetyl Phosphate, Ceteareth 10 Phosphate (need to
neutralize the phosphate surfactants)
Formulation Guidelines
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Salt stable LGNs normally need a PTT >60C
Always add salts, fragrances, and solvent preservatives below the PTT during cool down
Low HLB surfactants like Behenyl alcohol require milling above the PTT to promote optimal swelling
Adding LGN surfactants to the water phase normally produces smaller particle emulsions
Use blends of Cetyl and Stearyl alcohol when they are the only low HLB swelling surfactant used
(40:60 to 60:40)
The best LGNs are normally the most efficient that generate high viscosity at the lowest surfactant
concentration (5%-50-100K cps)
Large viscosity increases over time usually are the result of more lamellar phase being formed due to
unoptimized processing or surfactant ratio (excessive fatty alcohol hydrates)
LGN graininess after freeze/thaw stability testing can be caused by the high HLB surfactant
precipitating or crystalizing from the LGN. LGNs formed using Behenyl alcohol can also cause this.
Low levels of hydrophobically modified polymers can dramatically increase LGN viscosity (.05-.15%)
Always try different ratios of high to high plus low HLB surfactant ratios (10-30%)
References
• G. M. Eccelston, Multiple-phase oil-in-water emulsions, J. Soc. Comet. Cbem., 41, 122 (January/February 1990).
• G. M. Eccleston, The influence of fatty alcohols on the structure and stability of
creams prepared with polyethylene glycol 1000 monostearate/fatty alcohols, Int. J.
Cosmet. Set., 4, 133- 142 (1982).
• H. E. Junginger, Colloidal structures of o/w creams, Pharmaceut. Weekblad, 6, 141149 (1984).
• S. Fukushima, M. Yamaguchi, and F. J. Harusawa, Effect of cetostearyl alcohol on
stabilization of oil-in-water emulsions, Colloid Int. Set., 59, 159-165 (1977).