An official website of the United States government
Abstract Smart materials with coupled optical and mechanical responsiveness to external stimuli, as inspired by nature, are of interest for the biomimetic design of the next generation of soft machines and wearable electronics. A tough polymer that shows adaptable and switchable mechanical and fluorescent properties is designed using a fluorescent lanthanide, europium (Eu). The dynamic Eu‐iminodiacetate (IDA) coordination is incorporated to build up the physical cross‐linking network in the polymer film consisting of two interpenetrated networks. Reversible disruption and reformation of Eu‐IDA complexation endow high stiffness, toughness, and stretchability to the polymer elastomer through energy dissipation of dynamic coordination. Water that binds to Eu3+ions shows an interesting impact simultaneously on the mechanical strength and fluorescent emission of the Eu‐containing polymer elastomer. The mechanical states of the polymer, along with the visually optical response through the emission color change of the polymer film, are reversibly switchable with moisture as a stimulus. The coupled response in the mechanical strength and emissive color in one single material is potentially applicable for smart materials requiring an optical readout of their mechanical properties.
more »
« less
Dynamic Coordination of Eu–Iminodiacetate to Control Fluorochromic Response of Polymer Hydrogels to Multistimuli
Abstract New fluorochromic materials that reversibly change their emission properties in response to their environment are of interest for the development of sensors and light‐emitting materials. A new design of Eu‐containing polymer hydrogels showing fast self‐healing and tunable fluorochromic properties in response to five different stimuli, including pH, temperature, metal ions, sonication, and force, is reported. The polymer hydrogels are fabricated using Eu–iminodiacetate (IDA) coordination in a hydrophilic poly(N,N‐dimethylacrylamide) matrix. Dynamic metal–ligand coordination allows reversible formation and disruption of hydrogel networks under various stimuli which makes hydrogels self‐healable and injectable. Such hydrogels show interesting switchable ON/OFF luminescence along with the sol–gel transition through the reversible formation and dissociation of Eu–IDA complexes upon various stimuli. It is demonstrated that Eu‐containing hydrogels display fast and reversible mechanochromic response as well in hydrogels having interpenetrating polymer network. Those multistimuli responsive fluorochromic hydrogels illustrate a new pathway to make smart optical materials, particularly for biological sensors where multistimuli response is required.
more »
« less
- Award ID(s):
- 1705566
- PAR ID:
- 10049612
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 30
- Issue:
- 11
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Self-healing polymers often have a trade-off between healing efficiency and mechanical stiffness. Stiff polymers that sacrifice their chain mobility are slow to repair upon mechanical failure. We herein report adaptable polymer films with dynamically moisture-controlled mechanical and optical properties, therefore having tunable self-healing efficiency. The design of the polymer film is based on the coordination of europium (Eu) with dipicolylamine (DPA)-containing random copolymers of poly( n -butyl acrylate- co -2-hydroxy-3-dipicolylamino methacrylate) (P( n BA- co -GMADPA)). The Eu–DPA complexation results in the formation of mechanically robust polymer films. The coordination of Eu–DPA has proven to be moisture-switchable given the preferential coordination of lanthanide metals to O over N, using nuclear magnetic resonance and fluorescence spectroscopy. Water competing with DPA to bind Eu 3+ ions can weaken the cross-linking networks formed by Eu–DPA coordination, leading to the increase of chain mobility. The in situ dynamic mechanical analysis and ex situ rheological studies confirm that the viscofluid and the elastic solid states of Eu-polymers are switchable by moisture. Water speeds up the self-healing of the polymer film by roughly 100 times; while it can be removed after healing to recover the original mechanical stiffness of polymers.more » « less
-
null (Ed.)Adding metals into synthetic polymers is of broad interest to design multifunctional materials, particularly harnessing unique properties and functionalities not found in pure organic polymers. Other than simple emergence of the two, such hybridization often enables synergies to amplify the existing properties and/or create new properties not existing in either component. In this review, we highlight recent examples of metal/polymer hybrids based on either well-defined or ill-defined metal–ligand (M–L) coordination to design multifunctional materials. This review describes how in the hybridization of metal ions and polymers they complement each other synergistically in terms of their optical, mechanical and catalytic functionalities. Synthetic polymers once bound to metals enable stimuli-responsive properties of the metals and control over the luminescence of the metals in response to a change in the environment. As the second coordination sphere, synthetic polymers also enhance the reactivity of metal sites as a means to design bioinspired artificial enzymes. Additionally, the impact of the M–L coordination on the dynamic properties of polymers is summarized in the context of self-healable and tough materials built on the reversible network of interchangeable M–L coordination.more » « less
-
Abstract Smart hydrogels are a promising candidate for the development of next‐generation soft materials due to their stimuli‐responsiveness, deformability, and biocompatibility. However, it remains challenging to enable hydrogels to actively adapt to various environmental conditions like living organisms. In this work, supramolecular additives are introduced to the hydrogel matrix to confer environmental adaptiveness. Specifically, their microstructures, swelling behaviors, mechanical properties, and transparency can adapt to external environmental conditions. Moreover, the presence of hydrogen bonding provides the hydrogel with applicable rheological properties for 3D extrusion printing, thus allowing for the facile preparation of thickness‐dependent camouflage and multistimuli responsive complex. The environmentally adaptive hydrogel developed in this study offers new approaches for manipulating supramolecular interactions and broadens the capability of smart hydrogels in information security and multifunctional integrated actuation.more » « less
-
Abstract Ultralong afterglow emissions due to room‐temperature phosphorescence (RTP) are of paramount importance in the advancement of smart sensors, bioimaging and light‐emitting devices. We herein present an efficient approach to achieve rarely accessible phosphorescence of heavy atom‐free organoboranes via photochemical switching of sterically tunable fluorescent Lewis pairs (LPs). LPs are widely applied in and well‐known for their outstanding performance in catalysis and supramolecular soft materials but have not thus far been exploited to develop photo‐responsive RTP materials. The intramolecular LPM1BNMnot only shows a dynamic response to thermal treatment due to reversible N→B coordination but crystals ofM1BNMalso undergo rapid photochromic switching. As a result, unusual emission switching from short‐lived fluorescence to long‐lived phosphorescence (rad‐M1BNM,τRTP=232 ms) is observed. The reported discoveries in the field of Lewis pairs chemistry offer important insights into their structural dynamics, while also pointing to new opportunities for photoactive materials with implications for fast responsive detectors.more » « less
