Case studies
Case studies: placement questions applied to real formula problems
Seven formula problems discussed in public, analysed on paper. Each compares what an HLB-based review checks with what the TDA Logic placement checklist asks, and ends with a practical fix.
What are these case studies for?
TDA Logic is a placement framework for formulating on a fixed nanoscale architecture [preprint]. Its checklist asks, for every ingredient, about polarity at the formula’s pH, solubility, charge and molecular size, and then checks the formula against budgets for oil load, bilayer sites, ionic strength, free polymer and pH. See the placement procedure.
Those questions are not specific to one architecture. Several of them, charge, ionic strength, location, pH and polymer size, are the same questions that explain many failures in conventional emulsions and gels. Each case below takes a formula problem that was discussed in public, sets out what an HLB-based review would check, and shows which placement question would have flagged the problem at the design stage. The aim is to show where HLB arithmetic has no term for the cause, not to suggest that any formula built with TDA Logic is immune to failure.
How is each case structured?
Every case follows the same sequence: the problem; what an HLB-based reading checks; what a placement (TDA Logic) reading asks; a practical fix for the conventional formula; a takeaway; and a link to the public discussion on the In the field page. Chemistry figures, such as molar concentrations and undissociated fractions, are calculated on the page so that readers can check them. Use levels in the fixes refer to the conventional formula under discussion, not to any architecture.
The seven cases
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Case study 1 · Charge
Calcium bridging: a preservative blend that curdled an anionic cream
Calcium in a preservative blend bridged an anionic emulsifier and curdled a facial cream at 40 °C.
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Case study 2 · Ionic strength
Electrolytes and a lamellar cream that separated after small changes
Humectant salts, a chelator and an oil swap loosened a lamellar cream until it separated.
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Case study 3 · Location
A carrier that holds the preservative: cyclodextrin in a water-based serum
A cyclodextrin carrier and the finished pH set how much preservative is free to act in a serum.
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Case study 4 · Charge at the finished pH
Charge state decides it: a quaternary ammonium meets carbomer
A quaternary ammonium clumped with neutralised carbomer; at low pH the two coexist.
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Case study 5 · pH
Urea pH drift: an unbuffered system and a slowly hydrolysing ingredient
An unbuffered urea formula rose 1.65 pH units in a week; hydrolysis, buffering and contamination explain it.
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Case study 6 · Location
Micelle or droplet: why a shampoo’s fragrance did not stay on hair
A shampoo fragrance held in micelles rinsed away, while droplets are captured on hair.
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Case study 7 · Charge
Cationic and anionic in the same cream: a curl-defining hair product
An anionic emulsifying wax met a cationic surfactant, and anionic gums met a cationic polymer.
What do the cases have in common?
In each case the oil phase and the emulsifier choice, where there is one, were not the cause. The cause was a property that a selection rule does not carry: a multivalent ion inside a supplier blend, the ionic strength of humectant salts, a carrier that holds a preservative, the charge state of a polymer at a given pH, an ingredient that changes as it hydrolyses, or the structure an ingredient sits in at the moment of use. These are the variables the placement checklist is built around.