Shape-transformative materials that
can autonomously adopt three-dimensional
(3D) shapes in response to environmental stimuli are of interest for
the development of sensors and soft robotics. We herein report a new
synthetic strategy to fabricate shape-transformable Eu3+-containing interpenetrating polymer films consisting of poly(vinyl
alcohol) (PVA) and poly(3-iminodiacetate-2-hydroxypropylmethacrylate-co-acrylic acid) (P(IDHPMA-co-AA)). Given
the dynamic nature of Eu3+-iminodiacetate (IDA) coordination,
ink patterning and water/Fe3+ diffusion are used to generate
the in-plane or z-directional heterogeneities of
Eu-IDA dynamic coordination in the polymer film, respectively. The
heterogeneities can be visualized by the distribution of fluorescence
emission of Eu3+. When subjected to high humidity, the
differences in the swelling ratio and modulus as a result of chemical
inhomogeneity further drive various 3D shape morphings, including
rolling, helixing, twisting, surface buckling, and folding. Shape
transformation is reversible upon the removal of moisture from the
polymer films. The ink concentration and environmental humidity are
demonstrated to impact the shape transformation kinetics and the final
3D shape along with other geometric parameters. Our work illustrates
a novel way to fabricate new-generation biomimetic actuators and sensors.
New self-powered hydrogels that reversibly change electrical signals in response to circumambient multistimuli are of interest for the development of the next-generation smart sensing devices. In this work, a new...
We report a new design concept that utilizes the Ag+/Fe3+-catalyzed fast gelation of acrylic acid (AA)
or
AA/comonomer aqueous solutions (e.g., 56 s for the
gelation of the 20 wt % AA solution) to achieve fast healing of covalently
cross-linked polymer hydrogels. The fast-generated poly(acrylic acid)
(PAA) or AA copolymer hydrogel with a covalent network is highly active
for the interfacially igniting gelation (IIG) of AA or the AA/comonomer
in water through a frontal polymerization process. Using the AA or
AA/comonomer aqueous solution as the “repairing liquid,”
the fast-generated hydrogels (polymer concentration of 20 wt %) are
repeatedly healed at room temperature through the IIG reaction without
extra energy input. This IIG reaction-mediated healing (IIG-healing)
has healing efficiencies higher than 90%. The healing time can be
shortened from ∼60 min to only ∼1 min by increasing
the solid concentration of the fast-generated hydrogel to 92 wt %.
The IIG reaction also enabled the coating of a hydrophobic polymer
layer on the hydrogel, resulting in higher tensile strength, toughness,
and much better water retention capacity. We expect that this Ag+/Fe3+-catalyzed fast gelation strategy will pave
a facile and energy-efficient pathway to fabricate versatile and multifunctional
healing polymers.
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