posted on 2021-02-03, 21:09authored byKhaled Belal, François Stoffelbach, Dominique Hourdet, Alba Marcellan, Joel Lyskawa, Lieselot de Smet, Aurélien Vebr, Jonathan Potier, Graeme Cooke, Richard Hoogenboom, Patrice Woisel
Controlling
the swelling properties of hydrogels is of primary
importance for many applications ranging from actuators and valves
to tissue engineering and drug delivery. Herein, we report the use
of cyclobis(paraquat-p-phenylene) (CBPQT4+,4X–) as a versatile host to fine-tune the swelling
behavior of 1,5-dialkyloxynaphthalene guest containing poly(N,N-dimethylacrylamide) hydrogels (NaphtGelz) through
supramolecular host–guest complexation. While the equilibrium
swelling of NaphtGelz in water decreases with increasing amount of hydrophobic naphthalene
groups, the opposite behavior is observed with superabsorbing behavior
(up to 180 times their initial dry mass) upon immersion in aqueous
solutions containing the macrocyclic CBPQT4+,4X– due to formation of tetracationic host–guest complexes. In
this case, the swelling amplitude could be conveniently programmed
either by variation of the naphthalene content of the hydrogels or
by controlling the stoichiometry of the host–guest binding
events. Furthermore, by modifying the nature of the counterions (X
= Cl–, Br–, and I–) of the tetracationic CBPQT4+ macrocyclic host, the swelling
of the hydrogels could be tuned in line with Pearson’s absolute
hardness scale of X–. The swelling behavior of these
supramolecular hydrogels could be successfully described by a theoretical
model, taking into account the hydrophobic association of the naphthalene
groups and their screening by host–guest complexation. Finally,
addition of sodium dodecyl sulfate as a surfactant to the supramolecularly
swollen hydrogels led to a large decrease in hydrogel size due to
dissociation of the host–guest complexes and the formation
of CBPQT4+,4DS– within the hydrogel.