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