Reference

Glossary

Forty definitions covering the vocabulary of TDA Logic, the colloid science it rests on and the emulsifier-selection frameworks it is compared with.

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

This glossary fixes the meaning of the words used across the site. Framework terms follow the definitions in the primary reference; colloid and characterisation terms follow standard textbook usage, with a note where TDA Logic uses them in a particular way. Each entry has its own anchor, so a definition can be linked directly, for example /glossary#term-logd.

Claims about the framework carry one of four evidential labels: Specified Measured Modelled Not measured. Specified, measured and modelled are defined below; a property marked not measured has not been determined by experiment.

The framework and its vocabulary

TDA Logic#: Tri-Domain Architecture logic: a placement framework for leave-on cosmetics built on a fixed nanoscale architecture of three coexisting colloidal domains in a water phase. Each ingredient is routed to a destination by its logD at the formula’s pH, solubility and charge; the formula is then checked against loading budgets.
Placement rule#: A design rule that takes the colloidal structure as given and decides where each ingredient belongs within it. Its output is a destination per ingredient plus the resulting loading limits, not an emulsifier choice.
Selection rule#: A design rule whose output is a choice of emulsifier, or of conditions, that will build a colloidal structure. HLB, the Davies group-contribution method, PIT and HLD are selection rules in this sense: the surfactant system chosen determines droplet type and interfacial film.
Architecture (TDA sense)#: A colloidal structure built upstream and supplied complete, with its interfaces, particle populations and stabilisation already designed. Formulating on it means mixing ingredients into existing domains at room temperature, not rebuilding the carrier.
Destination#: Any of the four places to which TDA Logic assigns an ingredient: the nanocolloidal (oil-core) domain, the nanoliposomal (bilayer) domain, the nanomicellar domain or the water phase. An acceptable formula leaves no ingredient without a designed destination.
Domain#: In TDA Logic, a kinetically stabilised particle population that coexists with others in the continuous water phase, not a separate thermodynamic phase inside one droplet. The water phase is not counted as a domain.
Loading budget#: A capacity limit checked once every ingredient has a destination. TDA Logic names four: oil-core, bilayer, ionic-strength and free-polymer, with pH as a fifth, cross-cutting constraint. Budget values depend on the particular architecture and are modelled.
Anchoring site#: A position in a phospholipid bilayer able to accommodate the lipid tail of an amphiphilic ingredient. Because a bilayer offers a finite number of such positions, lipidated ingredients compete for them and are budgeted in moles rather than by weight.
Deposition (cosmetic sense)#: The amount of an ingredient that remains on the skin surface, in the outer stratum corneum or on the hair after application or rinsing. Deposition from a given product depends on its whole formula and needs that product’s own data.

Domains and destinations

Nanocolloidal (oil-core) domain#: The domain of nanoscale particles with a lipid core. It is the designed destination for high-logP ingredients such as emollient oils, oil-soluble vitamins and other lipophiles. Its capacity is set by the interfacial area available to carry added oil.
Nanoliposomal (bilayer) domain#: The domain of phospholipid vesicles. It is the designed destination for amphiphiles with a polar head and a lipid tail that seat in a bilayer, including palmitoyl- and myristoyl-lipidated peptides. Its capacity is a number of anchoring sites, counted in moles.
Nanomicellar domain#: The domain of micellar aggregates. It is the designed destination for surface-active ingredients and for ingredients carried in solubilised form, and its capacity is limited by how much the micelles can solubilise.
Water phase#: The continuous aqueous medium in which the three domains are dispersed, and the fourth destination. It receives humectants, glycols, water-soluble actives and extracts; its limits are the total water-soluble load and the ionic-strength budget for charged species.

Molecular properties used for placement

logP#: The base-10 logarithm of the partition coefficient of a compound’s neutral form between n-octanol and water. Higher values mean greater lipophilicity. It describes non-ionisable ingredients directly and the neutral species of ionisable ones.
logD#: The base-10 logarithm of the distribution coefficient: the octanol–water ratio of all forms of a compound, ionised and neutral, at a stated pH. For an ionisable ingredient, logD at the formula’s pH, not logP, governs placement under TDA Logic.
pKa#: The pH at which an ionisable group is half ionised. It links pH to charge and logD: a weak acid ionises progressively as pH rises above its pKa, so polarity and charge are judged at the finished pH.

Colloid stability

Ionic strength#: A measure of dissolved ions weighted by the square of their charge, I = ½ Σ cᵢzᵢ². A divalent ion therefore counts four times as much as a monovalent ion at the same concentration. Ionic strength sets the Debye length.
Debye length#: The distance, written κ⁻¹, over which electrostatic potential decays in an electrolyte. It shortens as ionic strength rises; for a 1:1 electrolyte in water at 25 °C, κ⁻¹ ≈ 0.304/√I nm, with I in mol/L.
Electrical double layer#: A charged particle surface together with the diffuse cloud of counter-ions that screens it in solution. When two particles approach, overlap of their double layers produces the repulsion on which electrostatic stabilisation relies.
DLVO theory#: The theory of colloid stability developed by Derjaguin and Landau and by Verwey and Overbeek, which adds van der Waals attraction to double-layer repulsion to give an energy barrier against aggregation. TDA Logic specifies kinetic stabilisation of its domains by such an electrostatic barrier.
Zeta potential#: The electrical potential at the slipping plane of a moving particle, usually estimated from electrophoretic mobility, and a practical indicator of surface charge. It is listed as a candidate method for characterising finished formulas; the preprint reports no zeta-potential values.
Schulze–Hardy rule#: The empirical finding that the counter-ion concentration needed to coagulate a charged colloid falls steeply as counter-ion valence rises. It explains why multivalent cations such as Ca²⁺ call for far more caution than Na⁺ near an anionic surface.
Bridging flocculation#: Aggregation in which one species links two particles: a multivalent ion binding anionic head groups on neighbouring surfaces, or a polymer chain adsorbed to two particles at once. Screening every ingredient for charge at the design stage is meant to catch it.
Depletion flocculation#: Aggregation caused by non-adsorbing free polymer or micelles that are excluded from the narrow gap between close particles, so that osmotic pressure pushes the particles together (Asakura and Oosawa 1954). Risk grows with molecular weight and concentration, hence the free-polymer budget.
Ostwald ripening#: Growth of larger particles at the expense of smaller ones as dispersed material diffuses through the continuous phase, driven by the higher solubility of material in small, strongly curved particles, as described by Lifshitz–Slyozov–Wagner theory. Oils with slight water solubility are especially prone to it.
Ripening inhibitor#: A component with very low solubility in the continuous phase, added to the dispersed phase so that loss of the more soluble component sets up an opposing composition gradient and slows Ostwald ripening (Kabalnov and Shchukin 1992).
Kinetic versus thermodynamic stability#: A thermodynamically stable system, such as a microemulsion, sits at equilibrium and can form spontaneously. A kinetically stable system is not at equilibrium but changes slowly because a barrier hinders aggregation. TDA Logic assumes kinetic stabilisation, not thermodynamic stability or spontaneous formation.

Characterisation and evidential labels

Dynamic light scattering (DLS)#: A technique that infers particle size from fluctuations in scattered light caused by Brownian motion, through the Stokes–Einstein relation. It reports an intensity-weighted hydrodynamic size and is the method used for batch measurements of the architecture.
Z-average#: The intensity-weighted harmonic mean hydrodynamic diameter given by cumulants analysis of DLS data. The primary reference specifies a particle-size design target of about 185 nm; the Z-average of each batch of the architecture is measured in-house.
Polydispersity index (PDI)#: A dimensionless width parameter from the same cumulants analysis; larger values indicate a broader size distribution. Because three particle populations are designed to coexist, a tri-domain system is expected to read broader than a single-population carrier.
Specified#: Evidential label for a property set by design rather than observed. In TDA Logic the particle-size target, the anionic surface charge, the DLVO stabilisation and the domain assignment of each ingredient are specified.
Measured#: Evidential label for a quantity obtained by experiment. Z-average and PDI of the architecture are measured in-house by DLS on every batch. The fractions of each ingredient present in each domain are not measured.
Modelled#: Evidential label for a value derived by calculation from a model rather than by observation. The loading limits of a tri-domain architecture are modelled.

Emulsifier-selection frameworks and conventional structures

HLB (hydrophile–lipophile balance)#: The scale introduced by Griffin (1949), usually running from 0 to 20, rating a surfactant by the balance of its water-loving and oil-loving parts, used to select emulsifiers for conventional emulsions. It has no term for particle size, surface charge or ingredient location.
Required HLB#: The emulsifier HLB that gives the most stable emulsion for a particular oil phase; a blend’s HLB is the weight average of its components. TDA Logic computes no required HLB, because no emulsifier is chosen.
Phase inversion temperature (PIT)#: The temperature at which an emulsion stabilised by nonionic surfactant inverts between oil-in-water and water-in-oil (Shinoda and Arai 1964). It is used to characterise nonionic systems and in low-energy emulsification.
HLD (hydrophilic–lipophilic deviation)#: An expression combining surfactant, oil, salinity and temperature terms that locates optimum formulation at HLD = 0 (Salager and colleagues 1979). It generalises HLB and PIT and, like them, is a framework for choosing emulsifiers and conditions.
Hansen solubility parameters (HSP)#: A split of cohesive energy into dispersion, polar and hydrogen-bonding components, placing materials in a three-dimensional space in which near neighbours tend to be compatible. HSP specifies no colloidal structure, but it can serve as an input to a TDA placement.
Lamellar gel network#: A structure formed by fatty alcohols and surfactant in water, in which swollen crystalline bilayers hold water and thicken a cream (Eccleston 1997). Electrolytes, changes to the oil phase and cooling history can all weaken it.
Coacervate#: A polymer-rich phase that separates when oppositely charged species associate, for example a cationic polymer with an anionic surfactant, typically on dilution in rinse-off products. Coacervates capture oil droplets rather than micelles, which bears on deposition from wash-off formulas.