am6b08374_si_005.avi (175.72 kB)
Poly(vinyl alcohol)–Tannic Acid Hydrogels with Excellent Mechanical Properties and Shape Memory Behaviors
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posted on 2016-09-20, 00:00 authored by Ya-Nan Chen, Lufang Peng, Tianqi Liu, Yaxin Wang, Shengjie Shi, Huiliang WangShape
memory hydrogels have promising applications in a wide variety of
fields. Here we report the facile fabrication of a novel type of shape
memory hydrogels physically cross-linked with both stronger and weaker
hydrogen bonding (H-bonding). Strong multiple H-bonding formed between
poly(vinyl alcohol) (PVA) and tannic acid (TA) leads to their coagulation
when they are physically mixed at an elevated temperature and easy
gelation at room temperature. The amorphous structure and strong H-bonding
endow the PVA–TA hydrogels with excellent mechanical properties,
as indicated by their high tensile strengths (up to 2.88 MPa) and
high elongations (up to 1100%). The stronger H-bonding between PVA
and TA functions as the “permanent” cross-link and the
weaker H-bonding between PVA chains as the “temporary”
cross-link. The reversible breakage and formation of the weaker H-bonding
imparts the PVA–TA hydrogels with excellent temperature-responsive
shape memory. Wet and dried hydrogel samples with a deformed or elongated
shape can recover to their original shapes when immersed in 60 °C
water in a few seconds or at 125 °C in about 2.5 min, respectively.