M. Benelmekki

On the origin of the electroactive poly(vinylidene fluoride) β-phase nucleation by ferrite nanoparticles via surface electrostatic interactions

Flexible multiferroic 0–3 composite films, comprising NiFe2O4 and CoFe2O4 ferrite nanoparticles in a polyvinylidene fluoride (PVDF) matrix, have been prepared by solvent casting and melt crystallization to investigate the polymer β-phase nucleation mechanism. Infrared spectroscopy confirms the nucleation of the polymeric electroactive β-phase with the addition of both ferrites, although the loading of ferrite nanoparticles needed to obtain the highest amount of β-phase was found to be one order of magnitude higher in the NiFe2O4/PVDF nanocomposites. Transmission electron microscopy imaging and thermogravimetric analyses indicate the formation of an interface in the nanocomposites with the β-phase nucleation. It is shown that the essential factor for the nucleation of the β-phase in the ferrites/PVDF nanocomposites is the static electric interaction between the magnetic particles with a negative zeta potential and the CH2 groups having a positive charge density.

Influence of ferrite nanoparticle type and content on the crystallization kinetics and electroactive phase nucleation of poly(vinylidene fluoride)

This work reports on the nucleation of the β-phase of poly(vinylidene fluoride) (PVDF) by incorporating CoFe(2)O(4) and NiFe(2)O(4) nanoparticles, leading in this way to the preparation of magnetoelectric composites. The fraction of filler nanoparticles needed to produce the same β- to α-phase ratio in crystallized PVDF is 1 order of magnitude lower in the cobalt ferrite nanoparticles. The interaction between nanoparticles and PVDF chains induce the all-trans conformation in PVDF segments, and this structure then propagates in crystal growth. The nucleation kinetics is enhanced by the presence of nanoparticles, as corroborated by the increasing number of spherulites with increasing nanoparticle content and by the variations of the Avramis exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticle content indicates that an important fraction of polymer chains are confined in interphases with the filler particle.

Interface characterization and thermal degradation of ferrite/poly(vinylidene fluoride) multiferroic nanocomposites

Flexible multiferroic 0–3 composite films, with CoFe2O4, Ni0.5Zn0.5Fe2O4 or NiFe2O4 ferrite nanoparticles as filler and polyvinylidene fluoride (PVDF) as the polymer matrix, have been prepared by solvent casting and melt crystallization. The inclusion of ferrite nanoparticles in the polymer allows to obtain magnetoelectric nanocomposites through the nucleation of the piezoelectric β-phase of the polymer by the ferrite fillers. Since the interface between PVDF and the nanoparticles has an important role in the nucleation of the polymer phase, thermogravimetric analysis was used in order to identify and quantify the interface region and to correlate it with the β-phase content. It is found that an intimate relation exists between the size of the interface region and the piezoelectric β-phase formation that depends on the content and type of ferrite nanoparticles. The interface value and the β-phase content increase with increasing ferrite loading and they are higher for CoFe2O4 and Ni0.5Zn0.5Fe2O4 ferrite nanoparticles. The composites shows lower thermal stability than the pure polymer due to the existence of mass loss processes at lower temperature than the main degradation of the polymer. The main degradation of the polymer matrix, nevertheless, shows increased degradation temperature with increasing ferrite content.

Design and characterization of Ni2+ and Co2+ decorated Porous Magnetic Silica spheres synthesized by hydrothermal-assisted modified-Stöber method for His-tagged proteins separation

The complete elimination of enzymes from the reaction mixture and the possibility of its recycling for several rounds result in great benefits, allowing the reduction of the enzyme consumption and their usability in continuous processes. In this work, it is evaluated the capture of a H6-tagged green fluorescence protein (GFP-H6) on porous magnetic spheres using the Co(2+) and Ni(2+) affinity adsorption as a possible cost-effective and up-scaled alternative way for the immobilization of His-tagged proteins. For this purpose, Porous Magnetic Silica (PMS) spheres were synthesized by one-step hydrothermal-assisted modified-Stöber method. The obtained spheres have a homogenous size distribution of 400 nm diameter. The γ-Fe(2)O(3) nanoparticles are homogenously distributed in the silica matrix. The obtained PMS spheres have a saturation magnetization of about 10 emu/g. Magnetophoresis measurements show a total separation time of 16 min at 60 T/m. The obtained PMS spheres were successfully and homogenously decorated with Co(2+) and Ni(2+) and then evaluated for the capture of a GFP-H6 protein. The results were compared with the performance of the commercial beads Dynabeads® His-Tag Isolation & Pulldown.

Improving the binding capacity of Ni2+ decorated porous magnetic silica spheres for histidine-rich protein separation

Biomagnetic immobilization of histidine-rich proteins based on the single-step affinity adsorption of transition metal ions continues to be a suitable practice as a cost effective and a up scaled alternative to the to multiple-step chromatographic separations. In our previous work, we synthesised Porous Magnetic silica (PMS) spheres by one-step hydrothermal-assisted modified-stöber method. The obtained spheres were decorated with Ni(2+) and Co(2+), and evaluated for the capture of a H6-Tagged green fluorescence protein (GFP-H6) protein. The binding capacity of the obtained spheres was found to be slightly higher in the case Ni(2+) decorated PMS spheres (PMSNi). However, comparing with commercial products, the binding capacity was found to be lower than the expected. In this way, the present work is an attempt to improve the binding capacity of PMSNi to histidine-rich proteins. We find that increasing the amount of Ni(2+) onto the surface of the PMS spheres leads to an increment of the binding capacity to GFP-H6 by a factor of two. On the other hand, we explore how the size of histidine-rich protein can affect the binding capacity comparing the results of the GFP-6H to those of the His-tagged α-galactosidase (α-GLA). Finally, we demonstrate that the optimization of the magnetophoresis parameters during washing and eluting steps can lead to an additional improvement of the binding capacity.

Magnetophoresis of colloidal particles in a dispersion of superparamagnetic nanoparticles: theory and experiments

Recent works have demonstrated the exciting possibility of inducing a tunable magnetic behavior in non-magnetic colloids by immersing them in a dispersion of superparamagnetic nanoparticles (NPs). Here we show experimentally that non-magnetic latex particles in a dispersion of superparamagnetic NPs experience a nontrivial, two-step “go and come-back” motion when brought under a uniform magnetic gradient. Our theoretical analysis indicates that the observed motion is due to the combined effect of the behavior of latex particles as magnetic holes and the adsorption of NPs at the latex surface. In agreement with theory, the NPs adsorption has been confirmed in our experiments by three independent experimental techniques (EDS, SEM and electrophoresis).

Contribution to the Study of Ferrite Nanobeads: Synthesis, Characterization and Investigation of Horizontal Low Gradient Magnetophoresis Behaviour

In this work we investigate the possibilities of the use of Horizontal Low Gradient Magnetic Field (HLGMF) (<100 T/m) for filtration, control and separation of the synthesized magnetic particles, considering, the characteristics of the suspension, the size and the type of nanoparticles (NPs) and focusing on the process scale up. Reversible aggregation is considered in the different steps of magnetic nanobeads synthesis. For these purpose, we synthesized Fe2O3‐silica core‐shell nanobeads by co‐precipitation, monodispersion and silica coating. SQUID, TEM, XRD, and Zeta potential techniques were used to characterize the synthesized nanobeads. An extensive magnetophoresis study was performed at different magnetophoretic conditions. Different reversible aggregation times were observed at different HLGMF, at each step of the synthesis route: Several orders of magnitude differences where observed when comparing citric acid (CA) suspension with silicon coated beads. Reversible aggregation times are correlated wit...