Nucleation of the electroactive phase of poly(vinylidene fluoride) by ferrite nanoparticles : surface versus size effects

Multiferroics and magnetoelectric materials show interesting scientific challenges and technnologial applications in sensors, acuators and data storage. In view of the fact that only a small number of materials show this kind of properties, exhaustive research activity is being pursued towards the development of new composite materials. Multiferroic nanocomposites films composed of piezoelectric poly(vinylidene fluoride) (PVDF) and magnetostrictive nano-size CoFe2O4, NiFe2O4 or NiZnFe2O4 ferrites were prepared by a solution method. Those ferrite nanoparticles have the ability to nucleate the electroactive -phase of the polymer, providing in this way an easy route for the preparation of magnetoelectric particulate composites. The fact that the different nanoparticles promotes different amount of -phase nucleation for different concentrations of nanoparticles indicates that filler size is not the most important parameter determining phase nucleation but the filler-matrix surface interaction. Further, when the polymer-ferrite surface interaction is modified through surfactation, the electroactive phase is not nucleated.The authors thank the Foundation for Science and Technology (FCT) through the 3º Quadro Comunitario de Apoio, the POCTI and FEDER programs and the PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007 projects. P. Martins thanks the support of the FCT (grant SFRH/BD/45265/2008

Platinum nanoparticles as pH sensor for intelligent packaging

Pt nanoparticles were produced by reverse micelle templating using DTAB. The resulting nanoparticles showes sizes between 250nm and 500nm and formed clusters. Thioglycolic acid (TGA) was covalently attached to the nanoparticle surface as a stabilizer and as. The Pt nanoparticles were dispersed in water and the dependence of its absorvance on the pH of the solution was studied. The spectra showed surface plamon absorption band at 280nm and also red shifted bands that were attributed to clusters of nanoparticles. It was found that the fraction of cluster population depends on the pH of the aqueous solution and that the response of the Pt nanoparticles to pH variations has a memory effect (hysteresis). The possibility of using these Pt nanoparticles in smart labels for food packaging is outlined.Fundação para a Ciência e a Tecnologia (FCT)FEDERCFUMProject NANO/NTec- SQA/0033/200

Study on oxidation layer of size controlled Nickel nanoparticles

Documento submetido para revisão pelos pares. A publicar em Nanoscale Research Letters. ISSN 1556-276XResearch on morphology and structure of oxidation layer of Ni nanoparticles (NPs) is reported. Ni NPs were obtained by wet chemical solution method and their size controlled in the nickel nucleation step using a non-ionic surfactant. Particles were about 50nm in size and polycrystalline. Combining high-angle annular dark field (HAADF) and electron energy loss spectroscopy (EELS), the nickel oxide layer was identified as not continuous and with non homogenous thickness

Simple analytical model for the magnetophoretic separation of superparamagnetic dispersions in a uniform magnetic gradient

Magnetophoresis-the motion of magnetic particles under applied magnetic gradient-is a process of great interest in novel applications of magnetic nanoparticles and colloids. In general, there are two main different types of magnetophoresis processes: cooperative magnetophoresis (a fast process enhanced by particle-particle interactions) and noncooperative magnetophoresis (driven by the motion of individual particles in magnetic fields). In the case of noncooperative magnetophoresis, we have obtained a simple analytical solution which allows the prediction of the magnetophoresis kinetics from particle characterization data (size and magnetization). Our comparison with new experimental results shows good quantitative agreement. In addition, we show the existence of a universal curve onto which all experimental results should collapse after proper rescaling. The range of applicability of the analytical solution is discussed in light of the predictions of a magnetic aggregation model

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

This work reports on the nucleation of the β-phase of poly(vinylidene fluoride), PVDF, by incorporating CoFe2O4 and NiFe2O4 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 one order of magnitude lower in the Cobalt 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 Avrami’s exponent. Further, the decrease of the crystalline fraction of PVDF with increasing nanoparticles content indicates that an important fraction of polymer chains are confined in interphases with the filler particle.Centro de Investigación Principe FelipeInstituto de Salud Carlos III (Ministry of Science and Innovation).FEDER funds through the "Programa Operacional Factores de Competitividade – COMPETE"Fundação para a Ciência e a Tecnologia (FCT) - NANO/NMed-SD/0156/2007, PTDC/CTM/69316/2006, SFRH/BPD/63148/2009Conselleria de Sanidad (Generalitat Valenciana)Spanish Ministry of Education through project No. MAT2010-21611-C03-01, EUI2008-0012

Hydrothermal assisted synthesis of iron oxide-based magnetic silica spheres and their performance in magnetophoretic water purification

Porous Magnetic Silica (PMS) spheres of about 400 nm diameter were synthesised by one-pot process using the classical Stӧber method combined with hydrothermal treatment. Maghemite nanoparticles (γ-Fe2O3) were used as fillers and cetyltrimethylammonium bromide (CTAB) was used as templating agent. The application of the hydrothermal process (120 °C during 48 h) before the calcination leads to the formation of homogeneous and narrow size distribution PMS spheres. X-ray diffraction patterns (XRD), Infrared measurements (FTIR) and Transmission Electron microscopy (TEM) methods were used to determine the composition and morphology of the obtained PMS spheres. The results show a homogeneous distribution of the γ-Fe2O3 nanoparticles in the silica matrix with a “hollow-like” morphology. Magnetophoresis measurements at 60 T m−1 show a total separation time of the PMS spheres suspension of about 16 min. By using this synthesis method, the limitation of the formation of silica spheres without incorporation of magnetic nanoparticles is overcome. These achievements make this procedure interesting for industrial up scaling. The obtained PMS spheres were evaluated as adsorbents for Ni2+ in aqueous solution. Their adsorption capacity was compared with the adsorption capacity of magnetic silica spheres obtained without hydrothermal treatment before calcination process. PMS spheres show an increase of the adsorption capacity of about 15% of the initial dissolution of Ni2+ without the need to functionalize the silica surface.Fundação para a Ciência e a Tecnologia (FCT

Horizontal low gradient magnetophoresis behaviour of iron oxide nanoclusters at the different steps of the synthesis route

In this work the use of Horizontal Low Gradient Magnetic Field (HLGMF) (<100T/m) for filtration, control and separation of synthesized magnetic nanoparticles (NPs) is investigated. The characteristics of the suspension, size and type of the NPs are considered and discussed. For these purposes, Fe2O3 silica coated nanoclusters of about 150 nm are synthesized by co-precipitation, monodispersion and silica coating. SQUID, TEM, XRD, and z potential techniques were used to characterize the synthesized nanoclusters. An extensive magnetophoresis study was performed at different magnetophoretical conditions. Different reversible aggregation times were observed at different HLGMF, at each step of the synthesis route. In particular, differences of several orders of magnitude were observed when comparing citric acid modified NPs with silica coated nanoclusters . Reversible aggregation times are correlated to the properties of the NPs at different steps of synthesis route.Fundação para a Ciência e a Tecnologia (FCT) - Bolsa NANO/NMed-SD/0156/2007, PTCD/CTM/69316/2006

Preparation of magnetoelectric composites by nucleation of the electroactive β-phase of poly(vinylidene fluoride) by NiZnFe2O4 nanoparticles

Composites consisting on poly(vinylidene fluoride), PVDF, and nano-size NiZnFe2O4 ferrites have been prepared by solution casting. The addition of NiZnFe2O4 nucleates the polar β-phase of PVDF, leading to magnetoelectric composites suitable for sensor and actuator applications. The amount of β-phase increases with increasing amount of nanoparticles up to filler concentrations of ~5%wt. For this concentration almost 90% of the crystalline phase of the polymer is in the electroactive β-phase. The nucleation occurs due to epitaxial crystallization at the nanoparticle surface, leading to variations in the crystallization kinetics and to the stabilization of the β-phase.The Portuguese Foundation for Science and Technology (FCT) for financial support under the POCTI and FEDER programs and the PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007 projects. P. Martins thanks FCT grant SFRH/BD/45265/2008

Nanoparticle dispersion and electroactive phase content in PVDF/ Ni0.5Zn0.5Fe2O4 nanocomposites for magnetoelectric applications

Ni0.5Zn0.5Fe2O4 ferrite/polyvinylidene fluoride composite films were prepared by a solution method and melt processing. As nanoparticle dispersion and polymer electroactive phase content are some of the key factors for improving magnetoelectric coupling in the composites, the dispersion of ferrite nanoparticles in the polymeric matrix was studied by preparing samples by two alternative dispersion routes: ultrasound and citric acid nanoparticle surfactation. The nucleation of the electroactive β-phase of the polymer was observed in composites produced by nanoparticle dispersion by ultrasound. This fact avoids the need of stretching composites at elevated temperature in order to obtain the electroactive phase and obtain magnetoelectric composites. By this method, nevertheless, large nanoparticle agglomerates are obtained. Nanoparticle dispersion is largely improved by citric acid surfactation of the nanoparticles. On the other hand, the β-phase of the polymer is not nucleated due to the modification of the nanoparticle-polymer interaction due to the presence of the surfactant

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 10 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 15 potential and the CH2 groups having a positive charge density.We acknowledge the Foundation for Science and Technology (FCT) for financial support through PTDC/CTM/69316/2006 and NANO/NMed-SD/0156/2007 projects. The authors also thank support from the COST Action MP1003, 2010 'European Scientific Network for Artificial Muscles'. P.M. and C.M.C. thank the support of the FCT (grants SFRH/BD/45265/2008 and SFRH/BD/68499/2010, respectively). M.B. thanks the FCT for support under the "Compromisso com a Ciencia" program