The applications of hydrogels are severely limited by their weak mechanical properties. Despite recent significant progress in fabricating tough hydrogels, it is still a challenge to realize high stretchability, toughness, and recoverability at the same time in a hydrogel. Herein, we develop a novel class of dual physically cross-linked (DPC) hydrogels, which are triggered by clay nanosheets and iron ions (Fe 3+ ) as cross-linkers. First, clay nanosheets induce the formation of the first cross-linking points through the interaction of hydrogen bonds with poly(acrylamide-co-acrylic acid) (PAm-co-Ac) chains. Then the secondary cross-linking points are introduced by ionic coordinates between Fe 3+ and −COO− groups of PAm-co-Ac polymer chains. The mechanical properties of DPC hydrogels can be tuned readily by varying preparation parameters such as clay concentration, Fe 3+ concentration, and molar ratio of Ac/Am. More importantly, the optimal DPC hydrogels possess high tensile strength (ca. 3.5 MPa), large elongation (ca. 21 times), remarkable toughness (ca. 49 MJ m −3 ), and good self-recoverability (ca. 65% toughness recovery within 4 h without any external stimuli). Thus, this work provides a promising strategy for the fabrication of novel tough hydrogel containing a dual physical cross-linked network.
Tough and transparent polyurethane networks with self-healing capability at mild temperature conditions were successfully prepared in a 1-pot procedure. The self-healing ability of synthesized polyurethane comes from the covalent disulfide metathesis and non-covalent H-bonding.The mechanical testing indicates that disulfide metathesis reforms the covalent bonds on a longer time scale, while H-bonding gives rise to a healing efficiency of around 46% in the early healing processing. The compromise between mechanical performance and healing capability is reached by tailoring the concentration of disulfide. The tensile strength of the sample with 100% self-heal efficiency can get to 5.01 MPa, which can be explained by higher mobility of polymer chain under ambient temperature from creep testing. In order to increase the tensile strength of self-healing elastomer, the hydrogen bonding effect received attention. H-bonding is a kind of noncovalent self-healing trending force; the supermolecular selfhealing elastomer based on H-bonding interaction was firstly developed by Leibler and colleagues. 16,17 Other researchers also have similar reports. 18,19 Although the self-healing effect of H-bonding is limited, the contribution to the self-healing cannot be ignored.This work focuses on obtaining a material with good mechanical properties and self-healing in 1-pot method by adapting the disulfide concentration. The self-healing contribution of disulfide metathesis and H-bonding effect of this system were investigated. To the best of our knowledge, disulfide self-healing assisted H-bonding selfhealing materials have not been systematically studied.2 | EXPERIMENTAL
| MaterialsPolytetramethylene ether glycol (PTMEG) with a number average molecular weight of 2000 g·mol −1 was provided by Aladdin IndustrialCorporation and was degassed for more than 3 hours at 90°C.
Passivation of electronic defects
on the surface and at grain boundaries
(GBs) of perovskite films has become one of the most effective tactics
to suppress charge recombination in perovskite solar cells. It is
demonstrated that trap states can be effectively passivated by Lewis
acid or base functional groups. In this work, nicotinamide (NTM, commonly
known as vitamin B3 or vitamin PP) serving as a Lewis base additive
is introduced into the PbI2 and/or FAI: MABr: MACl precursor
solution to obtain NTM modified perovskite films. It has been found
that the NTM in the perovskite film can well passivate surface and
GBs defects, control the film morphology and enhance the crystallinity
via its interaction with a lone pair of electrons in nitrogen. In
the presence of the NTM additive, we obtained enlarged perovskite
crystal grain about 3.6 μm and a champion planar perovskite
solar cell with efficiency of 21.72% and negligible hysteresis. Our
findings provide an effective route for crystal growth and defect
passivation to bring further increases on both efficiency and stability
of perovskite solar cells.
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