Connected, but for how long? A residual-lifetime criterion for the hydraulic–diffusive boundary in polyamide reverse-osmosis membranes
- 1V. I. Vernadskii Institute of General and Inorganic Chemistry, National Academy of Sciences of Ukraine
Abstract
The mechanism of water transport through the polyamide active layer of reverse-osmosis membranes is again contested: a 2023 claim that transport is governed by pore flow rather than solution-diffusion reopened a debate many considered settled, and a two-phase treatment has since shown the two descriptions are not mutually exclusive once their coefficients are matched. That reconciliation, however, answers a phenomenological question, not a structural one: whether a genuine, pressure-bearing continuous water phase exists is a separate, testable claim about the material. This Perspective argues that settling it requires two conditions prior work has largely treated as one — an instantaneous through-connected topology, and its survival over the transport timescale — and that the second condition has so far been estimated the wrong way: from the total lifetime of a connectivity interval rather than the residual lifetime seen by a water molecule arriving at a random instant, the same statistical root as the inspection paradox. A dynamic accessibility measure, Adyn = θ·SR(τtr), is proposed to close this gap, built on an intensive areal connectivity measure θ and a residual-lifetime survival function SR rather than an assumed exponential decay. A minimal structural surrogate places the connectivity transition at a model water-accessible volume fraction of 0.14–0.17, close to atomistic estimates for real polyamide, and a comparison of accessible simulation timescales with the residence time implied by realistic operating conditions shows why molecular dynamics alone cannot currently resolve the question. A concrete, falsifiable test agenda is proposed.
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BibTeX
@misc{kolomiiets2026connected,
title = {{Connected, but for how long? A residual-lifetime criterion for the hydraulic–diffusive boundary in polyamide reverse-osmosis membranes}},
author = {Ye. O. Kolomiiets and Yevhen Kolomiiets},
howpublished = {ChemRxiv},
year = {2026},
month = sep,
doi = {10.26434/chemrxiv.15008523/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008523/v1},
note = {CC BY},
}
RIS
TY - UNPB
TI - Connected, but for how long? A residual-lifetime criterion for the hydraulic–diffusive boundary in polyamide reverse-osmosis membranes
AU - Ye. O. Kolomiiets
AU - Yevhen Kolomiiets
PY - 2026
DA - 2026/09/08
PB - ChemRxiv
DO - 10.26434/chemrxiv.15008523/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15008523/v1
AB - The mechanism of water transport through the polyamide active layer of reverse-osmosis membranes is again contested: a 2023 claim that transport is governed by pore flow rather than solution-diffusion reopened a debate many considered settled, and a two-phase treatment has since shown the two descriptions are not mutually exclusive once their coefficients are matched. That reconciliation, however, answers a phenomenological question, not a structural one: whether a genuine, pressure-bearing continuous water phase exists is a separate, testable claim about the material. This Perspective argues that settling it requires two conditions prior work has largely treated as one — an instantaneous through-connected topology, and its survival over the transport timescale — and that the second condition has so far been estimated the wrong way: from the total lifetime of a connectivity interval rather than the residual lifetime seen by a water molecule arriving at a random instant, the same statistical root as the inspection paradox. A dynamic accessibility measure, Adyn = θ·SR(τtr), is proposed to close this gap, built on an intensive areal connectivity measure θ and a residual-lifetime survival function SR rather than an assumed exponential decay. A minimal structural surrogate places the connectivity transition at a model water-accessible volume fraction of 0.14–0.17, close to atomistic estimates for real polyamide, and a comparison of accessible simulation timescales with the residence time implied by realistic operating conditions shows why molecular dynamics alone cannot currently resolve the question. A concrete, falsifiable test agenda is proposed.
ER -