Soft Actuators based on MIL-88B(Fe) flexible MOF with Fast Response to Various Organic Solvent Vapor

Solvent vapor-driven soft actuators have been seen as promising devices for human-environment interaction and gained considerable attention in recent years. Considering the limited types of response solvent and the lack of quantification, MOF/polymer intelligent soft actuators may be a potential candidate of the fabrication of the bio solvent-driven actuators. Thus, this paper present a multiple solvent-driven soft actuator based on MIL-88B/PVDF asymmetric film, and also the comparison to the analogs based on other MIL-88(Fe) series flexible MOFs (including MIL-88A, 88C and 88D) was made for the deformation-structure relationship and the solvent-driven mechanism investigation. The deformation behavior to various organic solvent (including methanol, toluene and chloroform) of the MIL-88(Fe)/PVDF composite films have been investigated, and the structure and composition of the MIL88(Fe) fillers and the composite films were also characterized by SEM, FT-IR, and XRD. Based on the above results, the MIL-88B/PVDF composite which shows the diversity of response objects and the fast deformation response to most of the organic solvents through the solvent swelling/adsorption of the MOF skeleton, was used to fabricate a monolayer soft film composed by MIL-88B, carbon black (CB) and PVDF, namely MIL-88B/CB/PVDF. The MIL-88B/CB/PVDF film not only realizes the excellent deformation-discolor dual-responsive to methanol atmosphere with the visible deformation which could being quickly achieved within 1s under 10 vol % methanol atmosphere and the maximum crimp angle being up to 558o within about 50 s, and also a wide color change range including six view angle-dependent high saturation color (red, orange, yellow, green, blue and purple), but also shows an approximate linear relationship to three of the organic solvents (methanol, toluene and chloroform) between the maximum curl angle and the solvent concentration. Furthermore, several smart devices have also been fabricated, including the methanol-driven bionic petals, worm robot, alertor and LIG sensor. Therefore, such soft composites of flexible MOF and polymer have great potential in bio-robot and this work may provide new design strategy for the MOFs/polymer smart materials.