In the area of artificial hydrogels, simultaneous engineering of the volume transition characteristics and
mechanical properties of stimuli-responsive hydrogels is an important subject. By unrestricted architecting
of hierarchical structures, natural hydrogels are able to provide a wide range of swelling and
mechanical properties, beyond the limits of artificial hydrogels. Herein, a combination of nanostructures
and microstructures was developed to construct superporous hydrogels. Fibers of microfibrillated cellulose
(MFC), an eco-friendly reinforcing material, were used as nanostructures, aligned micropores were
used as microstructures, and in situ photopolymerization was used to immobilize the two structures
together within the gel networks of poly(N-isopropyl acrylamide) (PNIPAm). The introduction of MFC
distinctly enhanced volume transition, mainly by decreasing the swelling ratios above the transition. The
introduction of directional micropores increased the swelling ratio below the transition and decreased
the swelling ratio above the transition, thereby also enhancing the volume transition. Additionally, the
formation of aligned micropores achieved fast water infiltration, which is beneficial for superabsorbent
applications. The introduction of aligned micropores reduced the elastic modulus, but this could partially
be compensated for by reinforcement with MFC. This combination of crystalline nanofibers and
aligned micropores has great potential for the development of stimuli-responsive superporous hydrogels
outperforming current artificial hydrogels.
In the area of artificial hydrogels, simultaneous engineering of the volume transition characteristics andmechanical properties of stimuli-responsive hydrogels is an important subject. By unrestricted architectingof hierarchical structures, natural hydrogels are able to provide a wide range of swelling andmechanical properties, beyond the limits of artificial hydrogels. Herein, a combination of nanostructuresand microstructures was developed to construct superporous hydrogels. Fibers of microfibrillated cellulose(MFC), an eco-friendly reinforcing material, were used as nanostructures, aligned micropores wereused as microstructures, and in situ photopolymerization was used to immobilize the two structurestogether within the gel networks of poly(N-isopropyl acrylamide) (PNIPAm). The introduction of MFCdistinctly enhanced volume transition, mainly by decreasing the swelling ratios above the transition. Theintroduction of directional micropores increased the swelling ratio below the transition and decreasedthe swelling ratio above the transition, thereby also enhancing the volume transition. Additionally, theformation of aligned micropores achieved fast water infiltration, which is beneficial for superabsorbentapplications. The introduction of aligned micropores reduced the elastic modulus, but this could partiallybe compensated for by reinforcement with MFC. This combination of crystalline nanofibers andaligned micropores has great potential for the development of stimuli-responsive superporous hydrogels
outperforming current artificial hydrogels.
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