Solvent dependent solute solubility governs retention in silicone based organic solvent nanofiltration

• Solvent properties affect solute concentration inside PDMS material as well.
• Swelling of PDMS depends not only on the solvent used but also on the solute.
• High solute concentration in PDMS correlates with negative retentions.
• Flory–Huggins approach falls short to predict amount sorbed in the swollen polymer.

The application of silicon-based polymers as membrane material for organic solvent nanofiltration has grown over the last decade. A comprehensive understanding of this polymer as membrane material and its interaction with different solvent and solute systems is necessary to evaluate the transport properties. The solution diffusion mechanism covers solvent and solute transport through PDMS membranes. However, little is known about the solution part of the model. This work investigates swelling behavior of solvent/solute systems in PDMS being a representative for silicon-based polymers used today in industrial membranes. A gravimetric method measures remaining solute inside the polymer after solvent evaporation when equilibrium is reached. Three different solvents are evaluated as pure solvent, binary solvent mixtures and solvent/solute mixtures. Moreover, three different solutes are investigated: linear alkanes, polyethylene glycol and carboxylic acids. Swelling and solute concentration inside the polymer strongly depend on the solvent properties. Earlier observed negative retentions correlate with high solute solubility in the PDMS. It proves the importance of solvent dependent solute solubility in the retention mechanism in polymer based organic solvent nanofiltration.