Abstract
Localized electric fields have become, in recent years, a source of inspiration to researchers and laboratories thanks to a huge amount of applications derived from it, including positioning of microparticles as building blocks for electrical, optical, and magnetic devices. The possibility of producing polymeric materials with surface charge thus opens new perspectives for applications where process simplicity and cost-effectiveness of flexible electronics are of fundamental importance. In particular, the influence of surface charges is widely studied and is a critical issue especially when new materials and functional technologies are introduced. Here, we report a voltage-free pyro-electrification (PE) process able to induce a permanent dipole orientation into polymer sheets under both mono- and bipolar distribution. The technique makes use of the pyroelectric effect for generating electric potentials on the order of kilovolts by an easy-to-accomplish thermal treatment of ferroelectric lithium niobate (LN) crystals. The PE allows us to avoid the expensive and time-consuming fabrication of high-power electrical circuits, as occurs in traditional generator-based techniques. Since the technique is fully compatible with spin-coating-based procedures, the pyro-electrified polymer sheets are easily peeled off the surface of the LN crystal after PE completion, thus providing highly stable and freestanding charged sheets. We show the reliability of the technique for different polymers and for different applications ranging from live cell patterning to biofilm formation tests for bacteria linked to food-processing environments.
Highlights
The possibility of tailoring the material surface properties has allowed an increasingly active field for a wide variety of researches and applications ranging from materials science, nanotechnology, and electronics to biological and medical systems (Stuart et al, 2010)
We propose a simple and voltage-free process based on pyro-electrification (PE), capable of producing polar orientation and 2D polar patterning in freestanding polymer sheets
An electrostatic state appears and generates a high-intensity electric field at the crystal surface (Bhowmick et al, 2017) with mono- or bipolar properties depending on the nature of the lithium niobate (LN) crystal, mono-domain in the first case and periodically poled (PPLN) in the second one
Summary
The possibility of tailoring the material surface properties has allowed an increasingly active field for a wide variety of researches and applications ranging from materials science, nanotechnology, and electronics to biological and medical systems (Stuart et al, 2010). The most common approaches require an external voltage source as in the case of contact poling (Hill et al, 1994) or corona poling (Rychkov et al, 2011). In the case of contact poling, a large charge injection could produce a detrimental dielectric breakdown of the films (Hill et al, 1994; DeRose et al, 2006), while in the case of corona poling, the good homogeneity of the polarization is not guaranteed due to the difficult control of the high field intensity required. The poled films present often several surface damages due to various reactive and energy species, such as ozone or nitrogen oxides, that are produced by the corona discharge (Sprave et al, 1996)
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