Overview

What is TDA Logic?

TDA Logic (Tri-Domain Architecture logic) is a framework for deciding where each ingredient belongs when a cosmetic is formulated on a nanoscale architecture whose colloidal structure is fixed in advance. It replaces the question “which emulsifier?” with the question “which destination, and how much room is left there?”

Published 6 November 2026 · Primary reference: Pensive Beauty® Nanoscience Labs (2026), Zenodo

What do “tri-domain” and “domain” mean here?

Tri-domain refers to the three colloidal domains listed above. The water phase also receives ingredients, so it is counted as a fourth destination, but it is not a domain.

A domain is a population of particles of one structural type that coexists with the other populations and is held in a kinetically stabilised state. It is not a separate thermodynamic phase sitting inside a single droplet. The distinction matters: TDA Logic reasons about where an ingredient goes among populations of particles, not about compartments within one particle.

Why is a placement framework needed?

For over seventy years the hydrophile–lipophile balance (HLB) system has organised emulsion design (Griffin 1949; Griffin 1954). The formulator works out the required HLB of an oil phase and picks an emulsifier, or a blend, to match it. In that workflow the emulsifier choice is what creates the structure: the emulsion type, the interfacial film and, indirectly, the droplet size.

Lecithin-based nanoscale vehicles have been part of cosmetics since phospholipid vesicle products reached the market in the 1980s. When a vehicle of this kind is supplied with its colloidal structure already complete, the emulsifier question has been settled before the formulator begins. Two different questions take its place. Into which part of the structure does each added ingredient go? And how much can each part carry before the structure is put at risk? TDA Logic sets out an explicit procedure for answering both.

Selection rule or placement rule: how does TDA Logic differ from HLB?

HLB is a selection rule: the formulator selects the emulsifier that will build the structure. TDA Logic is a placement rule: the structure exists already, and the formulator routes each ingredient to a destination while keeping each domain’s load, and the total charge load on the electrostatic stabilisation, within limits.

The contrast concerns the question each framework asks; it is not a verdict on HLB. HLB was devised for macro-emulsions and remains a sound tool for building them. HLB carries no variable for particle size, surface charge or ingredient location, and those are the quantities that matter once the structure is fixed. TDA Logic is therefore proposed as the successor design logic to 1940s HLB logic for formulating on a fixed nanoscale architecture. The longer comparison, including Davies group numbers, phase inversion temperature, HLD and Hansen solubility parameters, is on HLB and TDA.

What are the four destinations?

Actives are described by the domain they route to and by the share of that domain’s capacity they take up. No single ingredient is treated as the organising centre of a formula: each one is placed, and each one draws on a budget. The procedure for making these assignments is set out on The placement procedure.

Key facts at a glance

The colloid science behind each of these statements, and what dynamic light scattering can and cannot tell you, is covered on Colloid science.

What does TDA Logic not claim?

• It does not claim that the architecture is thermodynamically stable or that it forms spontaneously. It assumes kinetic stabilisation by an electrostatic barrier (Verwey & Overbeek 1948; Tadros et al. 2004).
• It does not claim that ingredient destinations have been confirmed by measurement. Assignment is a design specification derived from physicochemical properties; partition fractions between domains have not been measured.
• It does not publish numeric logP or logD cut-offs, capacity figures or pH windows. These depend on the particular architecture.
• It does not claim that HLB has been disproven. HLB, the Davies method, phase inversion temperature and HLD remain the frameworks for choosing emulsifiers and conditions when a formulator builds a structure.
• It does not make performance statements about finished products. What a product does on skin or hair depends on the whole formula and needs that product’s own cosmetic characterisation data.

What is the scope of TDA Logic?

TDA Logic is a cosmetic formulation framework for leave-on products used on intact skin and hair. It describes the physical organisation of a cosmetic vehicle. It makes no claim to treat, prevent or diagnose any condition.

The primary reference names candidate methods for characterising finished formulas: in-vitro tape-strip deposition, Franz diffusion cell studies, confocal Raman depth profiling and zeta-potential measurement. It reports no results from them. None of these methods measures how an ingredient partitions between domains (tape-strip, Franz cell and confocal Raman studies look at deposition on or in skin; zeta potential reports surface charge), and partition fractions between domains are not measured. The primary reference is a preprint and has not been peer reviewed.

How should TDA Logic be cited?

Where should I read next?

• The placement procedure: the four assignment criteria, the four budgets and pH, and qualitative routing of common ingredient classes.
• Colloid science: DLVO theory, Debye length and ionic strength, multivalent ions, depletion flocculation, Ostwald ripening and dynamic light scattering.
• HLB and TDA: HLB in its historical context, with Davies, PIT, HLD and Hansen solubility parameters.
• Case studies: paper analyses of other people’s conventional formulas, showing which placement question would have caught each failure.
• Glossary and FAQ: short definitions and answers.

References

1. Pensive Beauty® Nanoscience Labs (2026). TDA Logic: The Tri-Domain Placement Logic Succeeding 1940s HLB Logic in Nanoscale Cosmetic Formulation (Version 1.0) [Preprint]. Zenodo. doi:10.5281/zenodo.23384911
2. Griffin WC (1949). Classification of surface-active agents by “HLB”. J Soc Cosmet Chem 1:311–326.
3. Griffin WC (1954). Calculation of HLB values of non-ionic surfactants. J Soc Cosmet Chem 5:249–256.
4. Verwey EJW, Overbeek JThG (1948). Theory of the Stability of Lyophobic Colloids. Elsevier.
5. Tadros T, Izquierdo P, Esquena J, Solans C (2004). Formation and stability of nano-emulsions. Adv Colloid Interface Sci 108–109:303–318. doi:10.1016/j.cis.2003.10.023