A Self‐Folding Polymer Film Based on Swelling Metal–Organic Frameworks

Abstract

Herein, we exploit the well-known swelling behaviour of metal-organic frameworks (MOFs) to create as elffolding polymer film. Namely,w es howt hat incorporating crystals of the flexible MOF MIL-88A into ap olyvinylidene difluoride (PVDF) matrix affords ap olymer composite film that undergoes reversible shape transformations upon exposure to polar solvents and vapours.S ince the self-folding properties of this film correlate directly with the swelling properties of the MIL-88A crystals,i ts electively bends to certain solvents and its degree of folding can be controlled by controlling the relative humidity.M oreover,i ts hows as hapememory effect at relative humidity values from 60 %t o9 0%. As proof of concept, we demonstrate that these composite films can lift cargo and can be used to assemble 3D structures from 2D patterns.O ur strategy is as traightforwardm ethod for designing autonomous soft materials with folding properties that can be tuned by judicious choice of the constituent flexible MOF.Among the most fascinating properties of certain metalorganic frameworks (MOFs) is their structural flexibility in response to external stimuli. Contrary to rigid crystalline porous materials (e.g.z eolites or aluminophosphates), the highly ordered networks of flexible MOFs,also known as soft porous crystals, [1] can undergo reversible dynamic structural transformations. [2] This flexibility arises from the reversible nature of the coordination bonds and weaker supramolecular interactions within MOFs,w hich allow for conformational changes of secondary building units and organic linkers.Over the past decade,this intriguing aspect of MOF chemistry has been investigated, leading to the discovery of numerous structural-transition phenomena, including thermal expansion, [3] linker rotation, [4] and subnetwork displacement. [5] Among the most interesting of flexible MOFs are swelling MOFs,w hich undergo expansion or contraction owing to adsorption or desorption, respectively. [6] Ap rime example is the isoreticular Fe III dicarboxylate MIL-88 family (MIL = Materials from Institute Lavoisier), in which the MOF unitcell volume exhibits reversible enlargement upon adsorption of polar solvent molecules owing to the formation of hydrogen bond interactions between guest molecules and the framework. [7] In these MOFs,t he swelling can be strongly influenced by the solvent and by the functional groups in the linkers. [8] Beyond molecular-level changes,aremarkable effect of such lattice swelling is the subsequent macroscopic deformation of the crystals. [8b] Our group considered that the aforementioned phenomenon had been overlooked in the development of functional materials,sowebegan to reflect on how such swelling might be exploited to develop novel soft materials capable of reversible shape transformations.I nt his regard, self-folding materials,which are able to translate external stimuli such as thermal, light, electrical, or chemical energy into useful and predictable shape transformations,are garnering attention for their po...

Guest-induced breathing mediated selective alcohol recovery from water by MIL-88A(Fe)

“…2e). This intermediate state was previously observed by Troyano et al 51 when MIL-88A(Fe) was exposed to different humidity atmospheric conditions. In this study, the sorption experiments were performed in aqueous media and thus, the as-synthesized MIL-88A(Fe) sample transits to the open form configuration (Fig.…”

Is Porosity at the MOF/Polymer Interface Necessarily an Obstacle to Optimal Gas-Separation Performances in Mixed Matrix Membranes?

“…In this context, there is a wealth of work covering the fabrication of MOF/polymer-based continuous films, with high MOF loading and homogeneous dispersion into the polymer matrices. ,,− Many other experimental studies have instead focused on testing MMMs’ performances for a range of gas mixture separations of utmost importance in the fields of natural gas upgrading and hydrocarbon recovery, regardless of their MOF contents and the MOF/polymer affinity (also called compatibility). ,− Meanwhile, the key microscopic parameters that control the onset of a good MOF/polymer compatibility have been identified thanks to the study of the interface structure of a series of MOF/polymer composites by computer simulations. , In contrast, the microscopic origin of the MMMs’ performances has not yet been unveiled, and in particular, the role of the MOF/polymer interface structure has not yet been determined.…”

Hierarchical porous metal–organic gels and derived materials: from fundamentals to potential applications

“…Recently, Troyano et al presented the synthesis of a hybrid film based on the flexible MOF MIL-88A(Fe) (Fe 3 O(OH)(H 2 O)(fumarate) 3 ) and polyvinylidene difluoride. 163 The synthesized film showed solvent and vapour assisted reversible shape conversion. Notably, the gel showed selective bending under impact of certain solvents, which can be controlled by varying relative humidity.…”