Didier Rouxel

Effect of ultrasonication and dispersion stability on the cluster size of alumina nanoscale particles in aqueous solutions

This study deals with the deagglomeration of nanoparticles in low concentration suspensions in water, protic polar solvent for polymers such as poly(vinyl alcohol) (PVA). The influence of the main parameters of ultrasonication such as time, power and irradiation modes (continuous, pulsed) on the cluster size of aluminium oxide nanoparticles 1 mg/ml in aqueous solutions was investigated. Power-law dependence of size reduction on ultrasonic time was observed. The study indicated an optimum power input, i.e. at higher vibration amplitude the break up of nanoparticle clusters was no better and there was a risk of reagglomeration occurring during a long ultrasonication. Under optimal conditions, continuous and pulsed irradiations showed almost the same efficiency of deagglomeration over a given time. This result provides alternative operating conditions for attaining the smallest size of the alumina aggregates in suspension. The influence of stabilization on the cluster size was also studied. Alumina nanoparticles were stabilized by electrostatic forces against reagglomeration without the need for dispersants, and the enhancement of dispersion stability using electrostatic, steric effects had no significant effect on the aggregate size. On the contrary, the adsorption of high molecular weight polyelectrolytes onto the particle surface could lead to reagglomeration due to material bridges between particle surfaces and even flocculation.

Dispersion of nanoparticles: from organic solvents to polymer solutions.

This work is devoted to a systematic study of nanoparticle dispersion by ultrasonication in different solutions: from organic solvents to polymer solutions. The cluster size of nanoparticles at different concentrations in both organic solvents and polymer solutions were directly characterized by Dynamic Light Scattering to study the effect of solid concentration, surfactant and polymer on the dispersion. It reveals that in stabilized suspensions, the smallest attainable size or aggregate size of nanoparticles is independent of solvent type and solid content over the tested range. Furthermore, nanoparticles in simple solvent and in polymer solutions had the similar evolution of cluster size and almost the same final size, which could be very helpful to optimize the dispersion of nanofillers in polymer solutions and nanocomposites. It is also shown that, with appropriate sonication amplitudes, the dispersion procedure developed for very dilute suspensions could be transferred to higher concentration suspensions or even to polymer suspensions.

Preparation and characterization of P(VDF-TrFE)/Al 2 O 3 nanocomposite

Hybrid nanocomposites based on crystalline nanoparticles dispersed in polymer matrix have been widely studied in the past few years because of the ability of these materials to combine the properties of organic polymer and inorganic nanoparticles. The aim of this work is to tune the mechanical properties of a piezoelectric polymer by adding nanoparticles to the matrix. In this paper, alumina nanoparticles were dispersed in the copolymer P(VDF-TrFE), which exhibits high piezoelectric coefficient after polarization under high electric field without needing stretching during the polarization process. Transmission electron microscopy and scanning electron microscopy demonstrate the high rate of welldispersed nanoparticles with 10% of alumina nanoparticles added to the matrix. Piezoelectric measurements indicate that P(VDF-TrFE) may be filled by up to 10 wt% of alumina while retaining its high piezoelectric properties and increasing its elastic constant by more than 20%, measured by Brillouin spectroscopy. This work opens a wide range of applications using nanoparticles with nonlinear optical, pyroelectric, magnetic, or ferroelectric properties.

Electrospun poly(vinylidene fluoride-trifluoroethylene)/zinc oxide nanocomposite tissue engineering scaffolds with enhanced cell adhesion and blood vessel formation

Piezoelectric materials that generate electrical signals in response to mechanical strain can be used in tissue engineering to stimulate cell proliferation. Poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), a piezoelectric polymer, is widely used in biomaterial applications. We hypothesized that incorporation of zinc oxide (ZnO )nanoparticles into the P(VDF-TrFE) matrix could promote adhesion, migration, and proliferation of cells, as well as blood vessel formation (angiogenesis). In this study, we fabricated and comprehensively characterized a novel electrospun P(VDF-TrFE)/ZnO nanocomposite tissue engineering scaffold. We analyzed the morphological features of the polymeric matrix by scanning electron microscopy, and utilized Fourier transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry to examine changes in the crystalline phases of the copolymer due to addition of the nanoparticles. We detected no or minimal adverse effects of the biomaterials with regard to blood compatibility in vitro, biocompatibility, and cytotoxicity, indicating that P(VDF-TrFE)/ZnO nanocomposite scaffolds are suitable for tissue engineering applications. Interestingly, human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells cultured on the nanocomposite scaffolds exhibited higher cell viability, adhesion, and proliferation compared to cells cultured on tissue culture plates or neat P(VDF-TrFE) scaffolds. Nanocomposite scaffolds implanted into rats with or without hMSCs did not elicit immunological responses, as assessed by macroscopic analysis and histology. Importantly, nanocomposite scaffolds promoted angiogenesis, which was increased in scaffolds pre-seeded with hMSCs. Overall, our results highlight the potential of these novel P(VDF-TrFE)/ZnO nanocomposites for use in tissue engineering, due to their biocompatibility and ability to promote cell adhesion and angiogenesis.

Electric, magnetic and optical limiting (short pulse and ultrafast) studies in phase pure (1 − x)BiFeO3–xNaNbO3 multiferroic nanocomposite synthesized by the pechini method

The perovskite (1 − x)BiFeO3–xNaNbO3 nanocomposite was successfully synthesized by Pechini method and crystallographic information was obtained from XRD and TEM analysis. Structural analysis using XRD and TEM shows that phase pure samples were obtained with reduced particle size. The observations reveal that particle size plays a crucial role in deciding the electric and magnetic properties. The multiferroic character of nanoparticles is confirmed through magneto electric (ME) coupling studies. The good coexistence of ferroelectric and ferromagnetic behaviors in the composite provides the possibility to achieve a measurable ME effect. The highest value of the magneto electric coefficient (α) is observed for x = 0.1 (α = 0.13 V cm−1 Oe−1) and it reduces for higher x values. Magnetization measurements for x = 0.1 show a small hysteresis at 6 K which also confirms the presence of the magnetic phase at low temperature while the usual antiferromagnetic behavior of BFO is found at 300 K. The reduced size and absence of impurity could be the reason for the enhancement in electrical properties. Low loss tangent values observed in the samples display a remarkable improvement. Open aperture Z-scan measurements reveal a nonlinear absorption behavior, which results in good optical limiting when excited with short pulse (nanosecond) as well as ultrafast (femtosecond) laser pulses.

Surface Acoustic Wave Device with Reduced Insertion Loss by Electrospinning P(VDF–TrFE)/ZnO Nanocomposites

Surface acoustic wave (SAW) devices have been utilized for the sensing of chemical and biological phenomena in microscale for the past few decades. In this study, SAW device was fabricated by electrospinning poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF−TrFE)) incorporated with zinc oxide (ZnO) nanoparticles over the delay line area of the SAW device. The morphology, composition, and crystallinity of P(VDF−TrFE)/ZnO nanocomposites were investigated. After measurement of SAW frequency response, it was found that the insertion loss of the SAW devices incorporated with ZnO nanoparticles was much less than that of the neat polymer-deposited device. The fabricated device was expected to be used in acoustic biosensors to detect and quantify the cell proliferation in cell culture systems.

Preparation and characterization of P(VDF-TrFE)/Al 2 0 3 nanocomposite

Hybrid nanocomposites based on crystalline nanoparticles dispersed in polymer matrix has been widely studied in the past few years because of the ability of these materials to combine both properties of organic polymer and inorganic nanoparticles. The aim of this work is to tune mechanical properties of piezoelectric polymer by adding nanoparticles to the matrix. In this paper alumina nanoparticles were dispersed in the copolymer P(VDF-TrFE) which exhibits high piezoelectric coefficient after polarization under high electric field without needing stretching during the polarization process‥ Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) demonstrate the high rate of well-dispersed nanoparticles. with ten percent of alumina nanoparticles added in the matrix. Piezoelectric measurements indicate that P(VDF-TrFE) may be filled up to 10 wt.% of alumina while keeping high piezoelectric properties and increasing of more than 10% the acoustic wave velocity of the material, measured by Brillouin spectroscopy. This work opens a wide range of applications using nanoparticles with nonlinear optical, pyroelectric, magnetic or ferroelectric properties.

Mapping of microwave-induced phonons by μ-Brillouin spectroscopy: hypersons in ZnO on silicon

High performance Brillouin microscopy has been used as a versatile method in order to characterize the spatial distribution of piezoelectrically induced acoustic fields excited at microwave frequencies in a ZnO film deposited on silicon. Filtering properties and acoustic field distribution emitted by inter-digital transducers as well as propagation losses are investigated by μ-Brillouin spectroscopy. It turns out that the acoustic field intensity decreases dramatically outside the immediate excitation area situated below the inter-digital finger structure.

Flexible over-moded resonators based on P(VDF-TrFE) thin films with very high temperature coefficient

This work presents for the first time a flexible over-moded resonator (OMR) based on P(VDF-TrFE) thin films. The devices were manufactured on commercially available elastic substrate with inkjet-printed electrodes. The sensing copolymer films used in the devices were polarized by the corona method after electrode deposition. The main performance parameters of the component were then determined. The manufactured OMRs on P(VDF-TrFE) exhibited a linear variation of frequency versus temperature and a very large value of temperature coefficient of frequency (TCF > 1600 ppm/°C). These properties suggest a great potential for using such components as low-cost and high-precision temperature sensors. The electromechanical coupling coefficient and the quality factor of the resonator were also characterized versus temperature.

CNRS School "Nanophysics for Health", 5-9 November 2012, Mittelwhir, France

Acknowledgements This supplement to Journal of Nanobiotechnology gathers eight tutorials corresponding to the topics of eight lectures given at the CNRS School entitled “Nanophysics for Health”, which took place in Mittelwhir, France, on 5 9 November 2012. The scope of the school was the implementation and relevance of tools and concepts from nanophysics applied to biological sciences and biomedical technologies. The onset of new, powerful methods for the investigation of biomolecular or cellular systems, as well as the development of innovative technologies for diagnosis or therapy are among the great promises of nanotechnologies in general, and of nanophysics in particular. This field of research is very dynamic and intrinsically multidisciplinary. It requires a tight collaboration between partners from different scientific horizons, which is favored by their sharing common, multidisciplinary scientific and technological skills. The goal of the school was to contribute to the building of this common scientific background and language. Fifty scientists (including lecturers) with diverse backgrounds in nanoscience, physics, biophysics, biology or chemistry attended the school. The program was essentially composed of keynote lectures focusing on three main topics: Nanophysics for Molecular Biology, Nanophysics for Cellular Biology, and Nanophysics for Diagnosis and Therapy. Practical sessions focusing on the use of Atomic Force Microscopy for the investigation of biological samples were also organized. In total, twelve 2-hour lectures were delivered, eight of them being published as tutorials in the present supplement of Journal of Nanobiotechnology. An introductory lecture (by D. Riveline) did present the manipulation of single molecules, and in particular the reasons why single molecule observation and manipulation are a unique tool to understand the dynamical properties of macromolecules. Then, a set of lectures was devoted to the structure, dynamics and dynamical assembly of proteins, including experimental developments in the firled of single molecule spectroscopy (B. Schuler), atomic force microscopy (F. Rico), and 3-dimensional imaging with electron microscopy (P. Schultz) as well as theoretical developments (K. Kruse). The last set of lectures showed that manufactured nanoparticles are very promising tools for nanomedicine, in the field of therapy (by P. Couvreur), as well as imaging and diagnosis (by F. Gazeau, L. Bonacina). For the school organizing committee, the guest editors: Jeremie Leonard, Didier Rouxel, Pascal Hebraud.