application of the hydrophile lipophile difference microemulsion model
DESCRIPTION
presented to American Oil Chemist's Society May 2014. We investigate whether the HLD concepts can be applied to the formulation of ready to use hard surface cleaners. What are the complications?TRANSCRIPT
Application of the HLD Microemulsion Modelfor the Development of Phase Stable SOWType Hard Surface Cleaner Formulation
105th AOCS Annual Meeting and Expo
Division of Surfactants and Detergents, Session 4.1b
May 4-7, 2014, San Antonio, TX
E. Szekeres, M.M. Knock, R. Zhang, R. Khan, and D.R. Scheuing
Outline
• Background on ready to use (RTU) cleaner formulations
• Goal and Strategy
• HLD model use for formulation support
• Experimental testing of model predictions
• Conclusions
RTU Cleaners and HLD model
• Ready to use (RTU) cleaners: hard surface spray cleaners, wipe lotions, etc.
• Typical Composition:
Surfactants below 5% (lower is preferred)
Electrolytes (buffering/pH adjustment agents, etc.)
Fragrance below ~ 0.3%
Lots of water water to oil ratio is extreme!
• Extreme high water to oil ratio may influence applicability of HLD model
• These systems are single phase, unsaturated microemulsions; may influence applicability of HLD model
We like our RTU cleaners sparkling clear
Phase separation causes clouding, inhomogeneity
Phase separation is typically driven by fragrance• Fragrance oils have low water solubility
• Surfactant micelles must solubilize fragrance well
Fragrance type impacts surfactant choice• Surfactant and fragrance oil hydrophobicity must be
appropriately matched
• Must have enough surfactant to completely solubilize the fragrance
• Surfactant system design can be very time consuming rely on HLD model to speed up work
Goal and Strategy
Goal
• Determine how well HLD model works for RTU surfactant design
Strategy
• Use the HLD model to select surfactants for a two-surfactant system that solubilizes a model fragrance oil
• Test the surfactant selection in the lab under realistic RTU conditions
• Compare HLD predictions with lab findings
• Observe limitations
Model system
Composition
• 2% model oil ( EACN = 5.3) – represents the fragrance
• 0.5% NaCl – represent electrolytes
• No alcohol/cosolvent
• Two surfactants - Use the HLD model for surfactant selection
Design Criteria
• Single phase system
• Robust to temperature change
• Minimized surfactant concentration
HLD model predicts microstructure of the self- assembly
HLDModel
Electrolyte
Oil
Surfactant
Temperature
Cosolvent
HLD value
Input Output
HLD > 0w/o
HLD < 0o/w
HLD = 0bicontinuous
Look for negative HLD, but close to zero
Two-surfactant formulation
Use HLD model• Select one hydrophobic surfactant with HLD > 0
• Select one hydrophilic surfactant with HLD < 0
• Determine optimized surfactant mixing ratio to get to o/w microemulsion region
• Ignore potential non-linearity of surfactant mixing
Go to the lab• Do surfactant mixing ratio scan with WOR ~ 1 system to
test surfactant hydrophobicities and optimized surfactant mixing ratio predicted by HLD model
• Do ratio scan under RTU conditions to see if predictions still hold
The HLD model equations
For anionic surfactants: choose this as the hydrophobic surfactant
For nonionic surfactants: choose this as the hydrophilic surfactant
𝐻 LD=𝑙𝑛 (𝑆 )−𝐸𝐴𝐶𝑁 ∙𝑘+𝐶𝑐−𝑎𝑇 ∙ (𝑇 −25 )+ 𝑓 ( 𝐴 )
H
ElectrolyteType/conc.
Oil type Surfactantparameters
Temperaturecoefficient
Cosolvent function
Electrolyte coefficientdepends on surfactant
Sign of temperatureterm opposite of anionic
Select anionic and nonionic surfactant for a model oil (EACN = 5.3)
Salinity, NaCl wt% 0.5
T, Celsius 20
Oil EACN 5.3
k 0.16
αT, 1/Celsius 0.01
Optimum Cc at 20C 1.49
Anionic surfactants*(Sulfonates, sulfosuccinates)
Non-ionic surfactants**(Ethoxylates)
Salinity, NaCl wt% 0.5T, Celsius 20Oil EACN 5.3k 0.16αT, 1/Celsius 0.1b 0.13Optimum Cc at 20C 1.28
at 2C : Cc optimum = 1.31
at 49C: Cc optimum = 1.78
at 2C: Cc optimum = 3.08
at 49C: Cc optimum = -1.62
Choose AOT as the hydrophobic surfactant (Cc = 2.55*) because its Cc > 1.78
Choose Surfonic L12-8 as the hydrophilic surfactant (Cc = - 5.7**) because its Cc < - 1.62
* Formulating with the HLD-NAC; by Edgar J. Acosta, April 25-27, 2012. Pleasanton, California, USA**based on Colloids and Surfaces A: Physicochem. Eng. Aspects 320 (2008) 193–204
Phase Inversion Predictions
0 5 10 15 20 25 30 35 40 45 500
0.2
0.4
0.6
0.8
1
Phase inversion (HLD = 0) predictions of the model at 5% surfactant
Temperature, C
AO
T w
eig
ht
rati
o w/o
o/w
• Formulation must remain o/w type across temperature range• Blue line shows phase inversion between 0.7 – 0.9 AOT
weight fraction• Model predicts only slight mixing ratio drift with temperature
WOR ~ 1 systems: Test tubes in line with HLD predictions
“Fish”-like conditions (WOR=1.94, 3% surfactant) at 20C
Surfonic L12-8 is hydrophilic as predicted
AOT is hydrophobic as predicted
Liquid crystals form near phase inversion
Model predicts phase inversion at AOT/Surfonic = 0.8Test tubes suggest phase inversion between AOT/Surfonic = 0.73 and 0.82
Ignoring synergy is not detrimental
AOT rich side
Surfonic rich side
w/o o/wInversionLC zone
3 phase system
RTU conditions: Test tubes in line with predictions
RTU cleaner-like conditions (WOR=40, 3% surfactant, 2% oil) at 20C
Surfactants keep their hydrophobicity/hydrophilicity
Liquid crystal impacted region expands
“formulation” to be shifted in the hydrophilic direction to avoid LC region
Liquid crystals obscure phase inversionPhase inversion remains around AOT/Surfonic = 0.73 and 0.82
Liquid crystals must be tracked for formula optimization
AOT side
w/o
o/w
o/w
Inversion/LC zone
Inversion/LC zoneSingle phase tube
Excess oil
AOT rich side
Surfonic rich side
RTU systems: optimizing robustness requires lab work
1.5 2 3 4 5 6 71 inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC
0.91 inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC0.82 inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC0.73 inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC inv/LC0.64 X O inv/LC inv/LC inv/LC inv/LC inv/LC0.55 X X O O inv/LC inv/LC inv/LC0.45 X X X O O O O0.36 X X X X O O O0.27 X X X X X O O0.18 X X X X X X O0.09 X X X X X X X
0 X X X X X X X
Total surfactant concentration, wt%
AO
T w
eigh
t ra
tio
HLD model outages: • Ignores liquid crystals – surfactant mixing ratio deviation between
model and experiment increases at higher surfactant concentrations• Doesn’t predict total surfactant concentrations (NAC model needed)
Phase behavior map of AOT, Surfonic L12-8, 2% model oil, 0.5% NaCl at T=20C
Testing the effect of temperature in lab
T=2C T=20C T=49C
1 inv/LC inv/LC inv/LC0.91 inv/LC inv/LC inv/LC0.82 inv/LC inv/LC inv/LC0.73 inv/LC inv/LC inv/LC0.64 inv/LC inv/LC inv/LC0.55 O O O0.45 X X O0.36 X X O0.27 X X X0.18 X X X0.09 X X X
0 X X X
• Model prediction of phase boundaries reflect realistic temperature effect trends
• Liquid crystals cause deviation between model and experimental data
3% surfactant
AO
T w
eigh
t ra
tio
Conclusions
• HLD model predictions quite worked well for WOR~1 systems
• For RTU type systems the HLD model gave Appropriate surfactant selection guidance,
Approximate surfactant mixing ratio range for optimization
Realistic temperature effect trends
• Liquid crystalline phases cause deviation; lab work necessary to stay away from LC regions
• Model gives good starting point for surfactant selection, and can help save time for product development
We could choose the surfactant(s) appropriatelyFor the oil to be solubilized
We could check the effect of temperature, salt, etc.To engineer sufficiently robust formulation
We would be able to select appropriate surfactants quickly
But we would have to still keep our lab coats!
So, if we knew the parameters……
Acknowledgments
Clorox
S&D Division, AOCS
Edgar Acosta for helpful discussions –
And You, The Audience and Consumer !
Appendix – Calculation of the optimum Cc parameters
0=𝑙𝑛 (𝑆 )−𝐸𝐴𝐶𝑁 ∙𝑘1+𝐶𝑐 1−𝑎𝑇 1 ∙ (𝑇 −25 )
Calculation of the optimum Cc parameters
0=𝑏 ∙𝑆−𝐸𝐴𝐶𝑁 ∙𝑘2+𝐶𝑐 2+𝑎𝑇 2 ∙ (𝑇 −25 )
For the anionic surfactant in the absence of alcohols the HLD equation becomes
At optimum 𝐻𝐿𝐷=0
𝐶𝑐 1=𝐸𝐴𝐶𝑁 ∙𝑘1− ln (𝑆 )+𝑎𝑇 1∙ (𝑇 −25 )Rearranging
For the non-ionic surfactant the HLD equation becomes
𝐶𝑐 2=𝐸𝐴𝐶𝑁 ∙𝑘2−𝑏 ∙𝑆−𝑎𝑇 2 ∙ (𝑇 −25 )
Rearranging
Appendix Predicting the optimum surfactant mixing ratio
𝐻𝐿𝐷1=𝑙𝑛 (𝑆 )−𝐸𝐴𝐶𝑁 ∙𝑘1+𝐶𝑐 1−𝑎𝑇 1 ∙ (𝑇 −25 )
Using linear mixing rule
𝐻𝐿𝐷2=𝑏∙𝑆−𝐸𝐴𝐶𝑁 ∙𝑘2+𝐶𝑐 2+𝑎𝑇 2 ∙ (𝑇 −25 )
=
where x = mole fraction of surfactant 1 (the anionic surfactant) in the anionic/non-ionic surfactant mixture
Term f(A) drops out of the HLD equations in the absence of alcohol
Subscript 1 refers to the anionic surfactantSubscript 2 refers to the non-ionic surfactant
At the phase inversion (optimum) point 𝐻𝐿𝐷𝑚𝑖𝑥=0
The surfactant mixing ratio that brings about the phase inversion (optimum)
𝑥∗=𝐻𝐿𝐷2
𝐻𝐿𝐷2−𝐻𝐿𝐷1