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 a self-folding polymer film. Namely, we show that incorporating crystals of the flexible MOF MIL-88A into a polyvinylidene difluoride (PVDF) matrix affords a polymer composite film that undergoes reversible shape transformations upon exposure to polar solvents and vapours. Since the self-folding properties of this film correlate directly with the swelling properties of the MIL-88A crystals, it selectively bends to certain solvents and its degree of folding can be controlled by controlling the relative humidity. Moreover, it shows a shape-memory effect at relative humidity values from 60 % to 90 %. As proof of concept, we demonstrate that these composite films can lift cargo and can be used to assemble 3D structures from 2D patterns. Our strategy is a straightforward method for designing autonomous soft materials with folding properties that can be tuned by judicious choice of the constituent flexible MOF.

Programmable Self‐Assembling 3D Architectures Generated by Patterning of Swellable MOF‐Based Composite Films

“…Prior to the sorption experiments, samples were degassed inside the chamber under vacuum at 120 °C for 6 h. Folding angles were calculated as previously described. [16] A Bluepoint 4 ECOcure (Hönle UV Technology) UV-Vis highintensity spot lamp without a filter (300 nm to 650 nm), and a PI 450 (Optris) infrared camera (operating temperature range: 0 ºC to 250 °C), were used. Data were obtained using PI Connect software.…”

“…These submicrometer-sized MIL-88A crystals (length: 510 ± 125 nm; width: 266 ± 57 nm) were then used to fabricate MIL-88A@PVDF films with a MOF content of 50 wt%, according to a previously reported method ( Figure S5, Supporting Information). [16] FESEM analysis revealed formation of a uniform film (thickness: 81 ± 5 μm) with an isotropic distribution of the MIL-88A crystals over the entire film ( Figure S6, Supporting Information). Note here that, although embedded MIL-88A crystals retain their reversible swelling behavior ( Figure S7 and S8, Supporting Information), their isotropic distribution induces an isotropic strain over the film, due to their expansion/contraction upon solvent adsorption/desorption, which provokes a negligible folding response ( Figure S5c, Supporting Information).…”

“…[14] Following this approach, we recently demonstrated that third-generation swellable metal-organic frameworks (MOFs) [15] _ENREF_36 can also be exploited to create humidity-driven self-folding polymer films (Figure 1a and Scheme S1, Supporting Information). [16] In these composite films (also known as mixed matrix membranes) [17] , the swelling response upon adsorption of heterogeneously distributed MIL-88A (MIL = Materials from Institut Lavoisier) crystals into a PVDF (polyvinylidene difluoride) polymer matrix generates an anisotropic strain over the composite film, causing the composite to fold. However, this approach is restricted to creation of a vertical gradient over the entire film, which limits the film actuation to simple uniaxial bending (Scheme S1, Supporting Information).…”

Phase-Selective Microwave Assisted Synthesis of Iron(III) Aminoterephthalate MOFs

“…Compared to other organic solvents, with tendency to the crystallization of MIL-88B-NH 2 . In this work, it has been presented an outstanding STY of 16000 kg•m −3 •d −1 at soft reaction conditions (T = 100 • C, t = 5 min), which exposes the beneficial use of MW-solvothermal assisted reaction for the industrial production of MIL-88B-NH 2 , which has demonstrated efficiency in applications such as photocatalysis, drug delivery and nanomotors [34][35][36][37]. In contrast, MIL-88B-NH 2 particles with better crystallinity were produced in DMF, and should not be discarded as reaction medium only due to its known toxicity and cost compared with the previously mentioned solvents.…”

Geometry Mismatch and Reticular Chemistry: Strategies To Assemble Metal–Organic Frameworks with Non-default Topologies

“…Numerous design approaches such as use of molecular building blocks (MBBs) or secondary building units (SBUs) [4][5][6][7][8][9][10] have been combined with the mathematic discipline of topology [11][12][13] to synthesize myriad novel porous structures, 14 including MOFs that exhibit high performance in crucial environmental and industrial applications such as energy/gas storage separation, [15][16][17][18] waste/valuables removal, 19,20 water harvesting [21][22][23][24][25] and smart materials. [26][27][28] Concerted efforts by chemists and materials scientists have given rise to a new subfield of chemistry: reticular chemistry. The dedicated Reticular Chemistry Structure Resource (RCSR) database created in 2008 by O'Keeffe and coworkers now contains roughly 3,000 three-periodic nets (topologies).…”