Polyfluorure de vinylidène | EPFL Graph Search

Le poly(fluorure de vinylidène) est un polymère du fluorure de vinylidène. Son nom anglais est « PolyVinyliDene Fluoride », ce qui explique son code ISO : PVDF. Il est commercialisé sous les noms Dyflor (Evonik), Foraflon, Kynar (Arkema) et Solef (Solvay). Le PVDF est un fluoropolymère thermoplastique semi-cristallin (taux de cristallinité voisin de 50 %) très résistant. À l'instar des autres fluoropolymères, il supporte les rayons ultraviolets, a une bonne résistance au feu et aux agents chimiques les plus corrosifs, et a d'ailleurs été utilisé en premier lieu pour l'isolation électrique. En 1969, le Kawaï découvre les propriétés piézolélectriques de ce polymère, ouvrant ainsi le champ à de nouvelles applications (transducteurs, batteries). Applications Les applications du PVDF sont multiples, mais limitées par son coût de fabrication. On l'utilise pour la tuyauterie, les accessoires et les cuves dans l'industrie chimique, l'isolation électrique de fils et d'éléments p

Adsorptive Removal of Pb(II) and As(V) from Aqueous Solution by PVDF/HMO Ultrafiltration Mixed Matrix Membrane

Younes Lucas Seghrouchni

Lead and arsenic are among the designated chemicals of major concern by the World Health Organization, they affect millions of people worldwide with both acute and chronic effects on human health. In the current study, mixed matrix membranes (MMMs) were fabricated using polyvinylidene fluoride (PVDF) for the matrix and hydrous manganese dioxide nanoparticles to remove lead, Pb(II), and arsenic, As(V), form water. The objectives of the study were to fabricate membrane with HMO:PVDF ratios from 0 to 1 and to characterize their adsorption properties on the two metals and their filtration performances. The HMO nanoparticles were synthesized using manganese sulfate monohydrate and potassium permanganate. The membranes were fabricated using phase inversion, a dope solution was prepared with HMO:PVDF ratios between 0 and 1, NMP as a solvent at an NMP:PVDF ratio of 5.57 and PVP at a PVP:PVDF ratio of 0.1 to increase the permeance of the membranes. The dope solution was casted and then soaked in a water coagulation bath for phase inversion. The structure of the nanoparticles was observed using TEM, and the structure of the membranes was described using SEM. The adsorption tests assessed the adsorption capacity, the adsorption kinetic and the effect of the pH on the adsorption capacity for the two metals. The concentration in the samples was measured with ICP-OES. A FTIR analysis was performed as a proof of adsorption. The tests that were run to assess the filtration performance of the membranes were the following ones: pure water permeance test, hydrophilicity test, surface analysis using XPS, pore size with AFM and finally filtration capacity on lead and arsenic. The HMO particles that were produced had sizes in the nanometer range and were elongated, which provided them a large surface-to-volume ratio. The membranes had asymmetric structures and the membrane with large HMO ratios had the surface of their pores covered uniformly with HMO particles. The adsorption capacities of pure HMO particles were 36 [mg/g] for arsenic and 283 [mg/g] for lead. The adsorption capacity of the membranes with an HMO:PVDF ratio of 1 was 11 [mg/g] for arsenic and 146 [mg/g] for lead. The Freundlich isotherm was used to describe the adsorption capacity of the membranes for both lead and arsenic. The adsorption kinetic was described by a pseudo-second order kinetic model for arsenic and the results were not significant enough the assess the adsorption kinetic model for lead. The equilibrium was almost reached in 30 minutes for the adsorption of the two metals on pure HMO. The adsorption capacity was enhanced with increasing pH for lead adsorption and it was the opposite for arsenic adsorption. The sensitivity to the pH was higher for lead compared to arsenic and this sensitivity to the pH could be used to regenerate the membrane in case of lead adsorption. The average permeance of the membranes was around 1500 [L/m2h bar], the pore sizes were in the ultrafiltration range, between 41 [nm] and 70 [nm] and the membranes were in the hydrophilic range, with an average contact angle of 69 [°]. The HMO ratio in the membranes had a limited impact on these three parameters. The filtration capacity on arsenic was too low to remove arsenic at ppb concentrations and the results of this test on lead were not significant enough to be interpreted.

2018

Towards room-temperature deterministic ferroelectric control of ferromagnetic thin films

Zhen Huang

The persisting demand of higher computing power and faster information processing keeps pushing scientists and engineers to explore novel materials and device structures. Within emerging functional materials, there is a focus on multiferroics materials and material-systems possessing both ferroelectric and ferromagnetic orders. Multiferroics with two order parameters coupled through a magnetoelectric interaction are of particular interest for novel information processing technologies. This thesis explores a promising concept of magnetoelectric multiferroic heterostructure incorporating separate ferroelectric and ferromagnetic thin layers with field-effect-mediated coupling through the heterointerface. The major issues related to ferroelectric control of ferromagnetism in multiferroic heterostructures addressed in this thesis include non-volatile magnetoelectric coupling at room temperature, deterministic switching of magnetization via polarization reversal, ferroelectric control of dynamics of magnetic domains and integration of ferroelectric gates on magnetic channels. The major accomplishments of this thesis are the following: Non-volatile ferroelectric control of magnetic properties has been demonstrated in ultra-thin Co layers at room temperature. The ferromagnetic transition Curie temperature, magnetic anisotropy energy and magnetic coercivity are shown to be switchable via the persistent field effect associated with the ferroelectric polarization. The magnitude of the effect is comparable or exceeds the results observed using the conventional (non-ferroelectric) gates. Local control of individual magnetic domain nucleation and propagation in Co channels by creating new ferroelectric domains has been achieved at the ambient conditions. The microscopic ferroelectric domains written on poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] ferroelectric polymer gate projected onto the magnetic channel changing locally the magnetic anisotropy energy, and consequently altering magnetic domain dynamics. Therefore it was possible to promote/impede magnetic domain nucleation and significantly change the domain wall velocity using a non-destructive and reversible procedure of ferroelectric domain writing. Non-volatile control of anisotropic magnetoresistance (AMR) has been demonstrated on diluted magnetic semiconductor (Ga,Mn)(As,P) thin films with integrated P(VDF-TrFE) ferroelectric gate. The field effect induced by the ferroelectric gate has shown the capability to strongly modulate the AMR behavior. Profound qualitative changes of the nature of AMR has been observed, including complete on/off switching of the crystalline component of AMR in (Ga,Mn)(As,P). A workflow for fabrication of integrated FET-type structures comprising a magnetic metal or semiconductor magnetic channel and ferroelectric polymer gate has been successfully developed. Different approaches for enhancement of ferroelectric gate operation were explored including integration of highly resistive hydrophobic interfacial layer and change of polymer composition for lower leakage. A significant increase of the non-volatile gate effect magnitude compared to the state of art was reached via improved quality of the ferroelectric/ferromagnetic interface.

EPFL2015

Ferroelectric Polymer Gates for Persistent Field Effect Control of Ferromagnetism in (Ga,Mn)As Layers

Sebastian Riester

The growing demand for higher computing power and element density continuously drives the development of novel device concepts. One group of materials currently attracting a lot of interest are the magnetoelectric multiferroics, due to their potential for creating devices with novel functionalities. These materials exhibit coupled ferroelectric and ferromagnetic behavior. Although the focus is on homogeneous multiferroics like bismuth ferrite, the stronger multiferroic coupling that is possible in composite multiferroics makes them attractive for many potential applications (e.g. spintronic logic and memory elements). In particular, electric field-mediated multiferroic composites promise worthwhile compatibility with CMOS circuitry. The present work explores a multiphase multiferroic system where the ferroelectric gate controls a dilute magnetic semiconductor (DMS) channel via the nonvolatile field effect associated with the spontaneous polarization. The system consists of a copolymer of vinylidene fluoride and trifluoroethylene [P(VDF-TrFE)] as the ferroelectric gate and an ultra-thin magnetic layer of (Ga,Mn)As which is one of the most well-established DMS and is considered a chief candidate for spintronic applications. The main outcomes of this research can be summarized as follows: A widely recognized incompatibility between ferroelectrics and group III-V semiconductors has been solved by the integration of a polymer ferroelectric onto a DMS in a multiferroic transistor configuration. Nonvolatile electric field control of ferromagnetism in a (Ga,Mn)As channel has been successfully demonstrated. Several pieces of evidence including the change of hysteretic properties, ferromagnetic Curie temperature shift and magnetoresistance behavior attest to the field effect-mediated multiferroic coupling in this system. Low ferroelectric gate operation voltages below 10 V were achieved through aggressive P(VDF-TrFE) thickness reduction without diminishing the gate effect strength. Polarization screening at the semiconductor/ferroelectric interface was identified as the main issue limiting the ferroelectric gate effect. A significant enhancement of the multiferroic coupling has been reached by thinning the (Ga,Mn)As channel down to 3 nm without compromising the ferromagnetic properties. From the Curie temperature response to ferroelectric gating, that follows the same trend for samples with thicknesses ranging from 3 to 7 nm, we conclude that the 2D limit has not been reached for the thinnest channels and the 3D models describing the ferromagnetic coupling are valid for this case. The ferroelectric control of ferromagnetism has been quantitatively interpreted in terms of existing models for hole-mediated exchange in (Ga,Mn)As.

EPFL2010