Fabrication of Piezoelectric Polymer and Metal–Organic Framework Composite Thin Films Using Solution Shearing

Polymer-metal–organic framework (polymer-MOF)
composites
have garnered significant interest as polymers can enhance the processability
and industrial applicability of MOFs. Thin films of these composites
are particularly attractive for applications in sensing, separations,
and flexible electronics. Solution shearing, a meniscus-guided coating
technique, has emerged as a scalable process for fabricating thin
films of MOFs, and can produce large-area films within minutes. In
this study, we utilized solution shearing to fabricate composite thin
films of a MOF UiO-66 and a piezoelectric polymer poly(vinylidene
fluoride-trifluoroethylene) (P(VDF-TrFE)), investigating how polymer
concentration during MOF synthesis and composite formation influences
thin film properties, including crystallinity, surface coverage, and
piezoelectric performance. Additionally, solid-state NMR spectroscopy
was utilized to probe the interactions between P(VDF-TrFE) and UiO-66
in the composite. Evidence from solid-state NMR indicated polymer-MOF
interactions, suggesting that the polymer strands are in close proximity
to the UiO-66 pores, supporting a mixed surface coating and pore infiltration
model. Furthermore, incorporating P(VDF-TrFE) enhanced the film’s
areal coverage from 70% to 100%. While the thermal conductivity remained
essentially unchanged, the composite film showed an improved piezoelectric
effect. The composite with 91 wt % P(VDF-TrFE) exhibited the highest
output voltage of 9.1 V and a sensitivity of 0.26 V/N under applied
pressure. This work demonstrates the potential of solution shearing
as a scalable technique for fabricating polymer-MOF composite thin
films.