# Evidence: Δχ effect

Parent: solvent-induced phase separation · class: phase behaviour · names merged here: delta chi effect; Δχ effect

3 papers measured or used it, 1 only mentioned it (of 207 kept papers). Papers in year order; each section heading ends with the paper's category / subcategory. Generated by tools/build_evidence.py from registry/concepts.csv and the cards; do not edit.

## 2010 Marsac — Effect of Temperature and Moisture on the Miscibility of Amorphous Dispersions of Felodipine and Poly(vinyl pyrrolidone) · Solid state stability / Physical stability

[2010-marsac-temperature-moisture-miscibility-felodipine-pvp-asd](../../../cards/2010-marsac-temperature-moisture-miscibility-felodipine-pvp-asd/paper.html) · Solid state stability / Physical stability · used · as: Δχ effect

| id | kind | content | locator |
|---|---|---|---|
| E1 | equation | Δχ effect (solvent-interaction asymmetry): abs(Δχ) = abs(χ12 − χ13) (printed with absolute-value bars) | p.182 |
| C36 | claim, prior hypothesis, authors: asserted; "may" | Solvent-induced phase separation (the Δχ effect, refs 39, 40) has a thermodynamic origin: when the interaction parameters of a solvent with two miscible components differ greatly, the solvent induces immiscibility; moisture may also promote phase separation in amorphous pharmaceutical systems (refs 31, 42) [rests on: cited: refs 31, 36-42; R25] | p.181 |
| C43 | claim, mechanism, authors: "well supported"; "There is clearly a large Δχ" | The thermodynamic origin is supported by polymer studies in which phase separation follows asymmetric interactions of two components with a solvent, as here: χ12 (water–felodipine) ≈3.3 against χ13 (water–PVP) ≈0.5 gives a large Δχ (E1), reflecting extremely unfavourable felodipine–water and more favourable PVP–water interactions, and mixing indeed decreases on moisture exposure or with water in the casting solvent [rests on: R22, R11, R13; cited: refs 39, 40, 44, 45] | p.182 |

## 2017 Purohit — Phase Behavior of Ritonavir Amorphous Solid Dispersions during Hydration and Dissolution · Dissolution / A. Release mechanism and LoC

[2017-purohit-ritonavir-asd-hydration-dissolution-phase-behavior](../../../cards/2017-purohit-ritonavir-asd-hydration-dissolution-phase-behavior/paper.html) · Dissolution / A. Release mechanism and LoC · used · as: Δχ effect

| id | kind | content | locator |
|---|---|---|---|
| E4 | equation | Δχ effect: Δχ = abs(χ_WD − χ_WP), stated in words as the magnitude of the difference between χ_WD and χ_WP; the larger Δχ, the higher the tendency for phase separation | pdf p.15 |
| C43 | claim, prior hypothesis, authors: asserted ("It has been found") | In the Flory-Huggins description (E2) water lowers the free energy entropically; a large positive χ means unfavourable interaction; χDP is negative or small for a molecular dispersion; χWD of a hydrophobic drug is large and positive while χWP is smaller (hydrogen bonding with water); a large Δχ (E4) gives a tendency to phase separate (Δχ effect, ref 31), here AAPS [rests on: cited: refs 30, 31; E2, E4] | pdf p.15 |
| C46 | claim, mechanism, authors: "can be expected"; "are expected" | PVP and PVPVA have hydrogen-bond acceptors but no donors, HPMCAS has both; RTV-HPMCAS interactions can be expected to be more numerous and diverse; with water, these interactions and the higher hydrophilicity of PVP and PVPVA are expected to give a higher Δχ for RTV-PVP and RTV-PVPVA [rests on: argument only; E4] | pdf p.15 |

## 2017 Saboo — Water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) amorphous solid dispersions: Insights with confocal fluorescence microscopy · Solid state stability / Physical stability

[2017-saboo-water-induced-miconazole-pvpva-asd-phase-separation](../../../cards/2017-saboo-water-induced-miconazole-pvpva-asd-phase-separation/paper.html) · Solid state stability / Physical stability · used · as: delta chi effect

| id | kind | content | locator |
|---|---|---|---|
| C43 | claim, mechanism, authors: "is likely"; "evidence is provided" | Water acts by altering the thermodynamics of the ASD on uptake (the delta chi effect) rather than only by raising mobility in a system already thermodynamically unstable: during film formation by solvent evaporation mobility is likely high at both low and high RH, which provides evidence for a thermodynamic role of water [rests on: R5, R6; cited: refs 10, 31, 36] | pdf p.20 |

## Mentioned only

- 2021 Saboo — [2021-saboo-tpgs-felodipine-pvpva-asd-release-high-loading](../../../cards/2021-saboo-tpgs-felodipine-pvpva-asd-release-high-loading/paper.html) · Dissolution / A. Release mechanism and LoC (ref 38)