Highly oriented poly(vinylidene fluoride-co-trifluoroethylene) ultrathin films with improved ferroelectricity

Abstract

We fabricated poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-TrFE) 75/25 mol% Langmuir–Blodgett (LB) nanofilms by the assistance of amphiphilic poly(N-dodecylacrylamide) (pDDA) nanosheets. The nanosheet is formed based on a well-organized hydrogen bonding network among pDDA amide groups at the air–water interface. By the introduction of the pDDA nanosheet, the film stability of the P(VDF-TrFE) Langmuir film was greatly improved with a twofold increase in the collapse surface pressure to 57 mN m⁻¹ of pure P(VDF-TrFE). Then, the P(VDF-TrFE) Langmuir film was endowed a good transfer ability with a unity transfer ratio irrespective of its non-amphiphilicity. Absorbance of the amide group of pDDA in UV-vis spectra shows a good linear relation with the film thickness. The result indicates that the multilayered film takes a uniform layered structure. The β-crystal content in as-prepared LB nanofilms with no post-treatment is up to 80%, one of the highest values ever reported. The monolayer thickness was determined as 3.5 nm by AFM measurements. The good film properties make the as-prepared P(VDF-TrFE)/pDDA LB ultrathin films (18 nm) available for ferroelectricity measurement using macroscopic methods such as the typical Sawyer–Tower circuit, which is usually challenging for other ultrathin films. The measurements demonstrate improved ferroelectricity, with a high remanent polarization value of 5.0 μC cm⁻² at 10 Hz.