MODELING CHARGE RELAXATION ON SURFACES OF PARTICLES SUSPENDED IN LIQUID

A general theory on charges relaxation process in particle-fluid systems is introduced in this article. The method to derive analytical solutions for the charge relaxation equation is illustrated, and some respects for this theory are discussed in detail.

Equilibrium charge and triboelectric coefficient of spheres in a rotating container

Contact electrification occurs in many granular material systems due to particle-particle and particle-wall contacts.In this paper,we used a simple device to characterize the electrification of different spheres in a rotating spherical container.The charge of the spheres was quantified by a Faraday cup after rotating for various time and the disperse behaviors of charged spheres were recorded by a camera.The effects of the rotational time,sphere size,rotational speed,sphere material,and relative humidity on the equilibrium charge and triboelectric coefficient were analyzed.The results show that the equilibrium surface charge density is independent of the sphere size and the rotating speed,whereas the larger rotating speed enhances the triboelectric coefficient.It is also shown that charge relaxation constants are two orders of magnitude lower than the charge generation constants for all spheres at a low relative humidity.The increase of water molecules in the air was found to result in the decline of charge generation constant and the rise of charge relaxation constant,which together cause the decrease of the equilibrium surface charge density.

Large-area atomic-smooth polyvinylidene fluoride Langmuir-Blodgett film exhibiting significantly improved ferroelectric and piezoelectric responses

Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett(LB)film results in severe space scatter in electrical,ferroelectric and piezoelectric characteristics,thus limiting the nanoscale research and reliability of nano-devices.However,no effective method aiming at large-area uniform organic ferroelectric LB film has ever been reported to date.Herein,we present a facile hot-pressing strategy to prepare relatively large-area poly(vinylidene fluoride)(PVDF)LB film with ultra-smooth surface root mean square(RMS)roughness is 0.3 nm in a 30μm×30μm area comparable to that of metal substrate,which maximized the potential of LB technique to control thickness distribution.More importantly,compared with traditionally annealed LB film,the hot-pressed LB film manifests significantly improved structure uniformity,less fluctuation in ferroelectric characteristics and higher dielectric and piezoelectric responses,owing to the uniform dipole orientation and higher crystalline quality.Besides,different surface charge relaxation behaviors are investigated and the underlying mechanisms are explained in the light of the interplay of surface charge and polarization charge in the case of nanoscale non-uniform switching.We believe that our work not only presents a novel strategy to endow PVDF LB film with unprecedented reliability and improved performance as a competitive candidate for future ferroelectric tunnel junctions(FTJs)and nano electro mechanical systems(NEMS),but also reveals an attracting coupling effect between the surface potential distribution and nanoscale non-uniform switching behavior,which is crucial for the understanding of local transport characterization modulated by band structure,bit signal stability for data-storage application and the related surface charge research,such as charge gradient microscopy(CGM)based on the collection of surface charge on the biased ferroelectric domains.