Toughening a Self-Healable Supramolecular Polymer by Ionic Cluster-Enhanced Iron-Carboxylate Complexes

Supramolecular polymers that can heal themselves automatically usually exhibit weakness in mechanical toughness and stretchability. Here we exploit a toughening strategy for a dynamic dry supramolecular network by introducing ionic cluster-enhanced iron-carboxylate complexes. The resulting dry supramolecular network simultaneous exhibits tough mechanical strength, high stretchability, self-healing ability, and processability at room temperature. The excellent performance of these distinct supramolecular polymers is attributed to the hierarchical existence of four types of dynamic combinations in the high-density dry network, including dynamic covalent disulfide bonds, noncovalent H-bonds, iron-carboxylate complexes and ionic clustering interactions. The extremely facile preparation method of this self-healing polymer offers prospects for high-performance low-cost material among others for coatings and wearable devices.     

High‐Power Actuation from Molecular Photoswitches in Enantiomerically Paired Soft Springs

Motion in plants often relies on dynamic helical systems as seen in coiling tendrils, spasmoneme springs, and the opening of chiral seedpods. Developing nanotechnology that would allow molecular‐level phenomena to drive such movements in artificial systems remains a scientific challenge. Herein, we describe a soft device that uses nanoscale information to mimic seedpod opening. The system exploits a fundamental mechanism of stimuli‐responsive deformation in plants, namely that inflexible elements with specific orientations are integrated into a stimuli‐responsive matrix. The device is operated by isomerization of a light‐responsive molecular switch that drives the twisting of strips of liquid‐crystal elastomers. The strips twist in opposite directions and work against each other until the pod pops open from stress. This mechanism allows the photoisomerization of molecular switches to stimulate rapid shape changes at the macroscale and thus to maximize actuation power.     

Die Volumenaufweitung beim uniaxialen Dehnen gefüllter Netzwerke

Zusammenfassung Es wird ein Modell vorgestellt, das es gestattet, die Volumenaufweitung zu berechnen, die beim unaxialen Dehnen einer Matrix mit kugelförmigen Füllstoffpartikeln auftritt. Es wird ein einfacher Zusammenhang zwischen Volumenaufweitung und Dehnung gefunden. Das relative Volumen nimmt mit der Dehnung zu, wobei der Füllstoffgehalt als einziger Parameter eingeht. Messungen an einer Modellsubstanz bestätigen die Richtigkeit der Rechnung.Bei der Untersuchung von rußgefülltem Gummi ergibt sich dagegen, daß der Füllstoff keine zusätzliche Volumenaufweitung gegenüber dem ungefüllten Gummi bewirkt. Wohl aber setzt bei rußgefülltem Kautschuk die dehnungsinduzierte Kristallisation früher ein als im ungefüllten System. Dies läßt sich mit Hilfe des Dehnungsdilatometers gut beobachten.

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A model is presented which allows one to calculate the increase in volume during uniaxial extension of a matrix containing a spherical filler. A simple relationship between volume increase and strain is found, where the filler concentration enters as the only parameter. Measurements on a model substance confirm this calculation.On the other hand, investigations of a carbon-black filled rubber show that the filler causes no additional volume increase over and above that for unfilled rubber. In the case of carbon-black filled rubber, however, straininduced crystallization sets in at lower degrees of elongation. This effect can be clearly observed by means of strain dilatometry.