Abstract
The presence of a solvent in a dense polymeric nanofiltration membrane layer can affect the macromolecular dynamics of the polymer material and the mobility of the solvent penetrant molecules. In addition, even the affinity of the swollen material for the solvent molecules can be distinct from that of the pure polymer material. These effects can substantially affect the membrane's performance. This paper provides sorption and swelling data of 9 thin polymer films that are commonly used for organic solvent nanofiltration (P84, Matrimid, PEI, PAN, PES, PSf, PEBAX, PTMSP, PDMS) swollen by 10 common solvents (hexane, toluene, dichloromethane, ethyl acetate, methyl ethyl ketone, acetone, isopropanol, ethanol, methanol, water). The paper describes the swelling dynamics during short-term solvent exposure (0–8 h), assesses the stability upon long-term solvent exposure (up to 2 months), and provides quantitative data on the solvent volume fractions inside the swollen layers. Among the surprising findings are the glubbery behavior of PTMSP and the completely different response of PES and PSf to toluene exposure. The results of this work demonstrate three crucial findings relevant to organic solvent nanofiltration membranes and other applications:
1.For many polymers, the swelling changes over long timescales of up to 2 months and longer. Results obtained on short timescales do however not always allow for direct extrapolation to longer time scales.2.Structural similarity of polymers does not guarantee similar swelling behavior.3.Swelling behavior of solvents cannot be solely explained by classifying solvents into aprotic, polar aprotic and polar protic solvents.
The results of this work can aid in constructing transport models and can help predicting polymer-solvent compatibility and membrane performance in OSN applications.
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•Many polymers do not reach equilibrium swelling after 2 months, not even for thin films.•Structural similarity of polymers does not guarantee similar swelling behavior.•Swelling behavior cannot be solely explained by classifying solvents into aprotic, polar aprotic and polar protic solvents.•PTMSP behaves like a ‘glubber’.