Confinement Induced Preferential Orientation of Crystals and Enhancement of Properties in Ferroelectric Polymer Nanowires

Abstract

The physical properties of polymers strongly depend on the molecular or supermolecular order and orientation. Here we demonstrate the preferential orientation of lamellar crystals and the enhancement of ferro/piezoelectric properties in individual poly-(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) nanowires fabricated from anodic alumina oxide (AAO) templates. The crystallographic a axis of P(VDF-TrFE) was found to be aligned along the long axis of nanowires due to geometrical confinement and grapho-expitaxial crystals growth. The alignment of lamellar crystals in P(VDF-TrFE) nanowires and enhancement of crystallization translated into improved ferro/piezoelectric properties such as lower coercive field and higher piezoelectric coefficient, testified by piezoresponse force microscopy images and piezoresponse hysteresis loops.

Nanostructured polymer-based piezoelectric and triboelectric materials and devices for energy harvesting applications

“…To examine the crystallization of as-synthesized NWs, freed NWs (AAO template dissolved by aqueous phosphoric acid solution) were characterized by XRD with diffraction patterns reflecting only (2 0 0) and (1 1 0) planes of crystalline phase β, as compared with parent P(VDF-TrFE) powder samples showing peaks of all α, β, γ phases ( figure 7(b)). The stronger β phase character of the NWs was believed to be solely due to the confinement effect of the nanoporous template [19,20,26,62,66,67], which was beneficial to their subsequent implementation into NGs. Template-grown P(VDFTrFE) NWs still embedded within the template were then incorporated into an NG, by sputtering platinum electrodes on both sides of the nanowire-filled template, followed by encapsulation in poly(dimethylsiloxane) (PDMS) (figure 7(c)).…”

Observation of Confinement‐Induced Self‐Poling Effects in Ferroelectric Polymer Nanowires Grown by Template Wetting

“…Nanowires and other nanostructures of PVDF and P(VDF‐TrFE) are of particular interest as they have been reported to exhibit enhanced properties including higher ferroelectric crystallinity, higher piezoelectric coefficients, and lower coercive fields as well as being capable of being fabricated readily orientated with aligned dipoles without the requirement for further post‐fabrication poling processes . This “self‐poled” nature being intrinsic in the fabrication process is highly advantageous as the large electric fields (≈50 MV m −1 ) and high temperatures otherwise involved in poling may be difficult to achieve in practice.…”

“…Electrospinning, nanoimprinting, and template‐wetting fabrication methods have all been reported to produce readily orientated piezoelectric polymers in confined geometries. Template wetting, where the polymer wets and fills a nanoporous template either from the melt or solution, has benefits over the alternative fabrication methods due to its simplicity and the lack of the need of specialized equipment, large electric fields, and/or high temperatures.…”

“…Template wetting, where the polymer wets and fills a nanoporous template either from the melt or solution, has benefits over the alternative fabrication methods due to its simplicity and the lack of the need of specialized equipment, large electric fields, and/or high temperatures. Under suitable conditions, the confined geometry results in the polymer self‐assembling into an orientated material structure of stacked lamellae to give rise to “self‐poled” nanowires . This is in contrast with electrospinning where the inherent mechanical stretching and large electric fields involved are believed to be responsible for the resulting orientated material …”

Controllable Hierarchical Surface Patterns of Supramolecular Hydrogels: Harnessing Buckling Instability by Confinement

“…[11] This in turn translates into desirable properties such as stronger mechanical strengthi ns tructural polymers, [12] higherc arrier mobility in semiconducting polymers, [13] and lowerc oercivef ield strengthi nf erroelectric polymers. [14,15] The other strategyf or directly patterning functional polymers is to take advantage of surface instability of polymer thin films. Surface instabilities in polymer thin films on as ubstrate can spontaneously occur on the microscale or nanoscale exemplified by dewetting, [16] phase separation, [17] and wrinkles, [18] or can be inducedb ya pplying an externals timulus, such as an electric field, at hermalg radiento rb ubbleso nt he thin films.…”