  Hydrogels which are hydrophilic and porous materials have recently emerged as
promising systems for filtration applications. In our study, we prepare
hydrogel membranes by the photopolymerization of a mixture of poly (ethylene
glycol) diacrylate (PEGDA) and large poly(ethylene glycol) (PEG) chains of 300
000 g.mol-1 in the presence of a photoinitiator. We find that this addition of
free PEG chains induces a large and non-linear increase of the water
permeability. Indeed, by changing the content of PEG chains added, we obtain
variations of the hydrogel water permeability over two orders of magnitude. The
highest water permeability values are obtained for the membranes when the PEG
concentration is equal to its critical overlap concentration C*. Moreover, we
find that the flow rate of water through the membranes varies non-linearly with
the pressure. We relate this result to the deformability of the membranes as
the applied pressure leads to a compression of the pores. This study provides
new perspectives for the design of flexible hydrogel membranes with controlled
permeability and their application in water treatment and bioseparation.
