Nano-micro compositemagnetic fluids: Magnetic andmagnetorheologicalevaluation forrotating seal and vibration damper applications

Journal of Magnetism and Magnetic Materials, Volume 406, 15 May 2016, Pages 134-143

Abstract:In this paper, static magnetic properties and magnetorheological behavior of a set of 12 nano-micro composite magnetic fluids (CMFs) were studied. The samples with a ferromagnetic particle volume fraction ranging in a large interval image were prepared by adding carbonyl iron powder in a highly concentrated transformer oil-based ferrofluid (FF). The ferrofluid has the magnetite volume fraction of image and saturation magnetization of image (930 Gs). No further additives were used in order to prevent sedimentation. It was noticed an increase of the static yield stress, of about 3 orders of magnitude, with the increase of the total solid volume fraction of samples and with the increase of the magnetic field, which varied between 0 kA/m and 950 kA/m. The dynamic yield stress (Herschel-Bulkley model) image of the samples strongly increases with the magnetic field and shows a slight tendency of saturation for higher intensities of the magnetic field. There is a less pronounced increase of image, about an order of magnitude with the increasing volume fraction of the iron particles. The relative viscosity increase induced by the magnetic field reaches a maximum for both considered shear rates: image and image and it was revealed an optimal volume fraction of Fe particles, image, corresponding to a total volume fraction of image, at which the magnetoviscous effect has its maximum value. The magnetic properties and also the magnetorheological and the magnetoviscous behavior of highly concentrated ferrofluid-based CMFs can be controlled by the addition of iron microparticles in order to attain the optimal concentration for the envisaged engineering applications, rotating seals and magnetorheological vibration dampers.

Probing droplets with biological colloidal suspensions on smart surfaces by synchrotron radiation micro- and nano-beams

Optics and Lasers in Engineering, Volume 76, January 2016, Pages 57-63

Abstract:Droplets with colloidal biological suspensions evaporating on substrates with defined wetting properties generate confined environments for initiating aggregation and self-assembly processes. We describe smart micro- and nanostructured surfaces, optimized for probing single droplets and residues by synchrotron radiation micro- and nanobeam diffraction techniques. Applications are presented for Ac-IVD and β-amyloid (1–42) peptides capable of forming cross-β sheet structures. Complementary synchrotron radiation FTIR microspectroscopy addresses secondary structure formation. The high synchrotron radiation source brilliance enables fast raster-scan experiments.

Adapting Nanotech Research as Nano-Micro Hybrids Approach Biological Complexity, A Review

Journal of Materials Science & Technology, Volume 32, Issue 5, May 2016, Pages 387-401

Abstract:Today's emergence of nano-micro hybrid structures with almost biological complexity is of fundamental interest. Our ability to adapt intelligently to the challenges has ramifications all the way from fundamentally changing research itself, over applications critical to future survival, to posing globally existential dangers. Touching on specific issues such as how complexity relates to the catalytic prowess of multi-metal compounds, we discuss the increasingly urgent issues in nanotechnology also very generally and guided by the motto ‘Bio Is Nature's Nanotech’. Technology belongs to macro-evolution; for example integration with artificial intelligence (AI) is inevitable. Darwinian adaptation manifests as integration of complexity, and awareness of this helps in developing adaptable research methods that can find use across a wide range of research. The second half of this work reviews a diverse range of projects which all benefited from ‘playful’ programming aimed at dealing with complexity. The main purpose of reviewing them is to show how such projects benefit from and fit in with the general, philosophical approach, proving the relevance of the ‘big picture’ where it is usually disregarded.

Semiconductor-to-metallic flipping in a ZnFe2O4–graphene based smart nano-system: Temperature/microwave magneto-dielectric spectroscopy

Materials Characterization, Volume 99, January 2015, Pages 254-265

Abstract:Zn-(FeO2)2–graphene smart nano-composites were synthesized using a novel modified solvothermal synthesis with different percentages of graphene. The structure of the nanocomposite was confirmed through X-ray diffraction, micro-Raman scattering spectroscopy, Ultraviolet–Visible spectroscopy, and Fourier transform infrared spectroscopy. The structural growth and morphological aspects were analyzed using scanning/transmission electron microscopy, revealing marvelous micro-structural features of the assembled nano-system resembling a maple leaf. To determine the composition, energy dispersive spectroscopy and X-ray photoelectron spectroscopy were used. Microwave magneto-dielectric spectroscopy revealed the improved dielectric properties of the nano-composite compared to those of the parent functional nanocrystals. Temperature gradient dielectric spectroscopy was used over the spectral range from 100 Hz to 5 MHz to reveal the phenomenological effect that the nanosystem flips from its usual semiconductor nature to a metallic nature with sensing temperature. Electrical conductivity and dielectric analysis indicated that the dielectric loss and the dielectric permittivity increased at room temperature. This extraordinary switching capability of the functionalized graphene nanosystem opens up a new dimension for engineering advanced and efficient smart composite materials.

Strain gradient shell model for nonlinear vibration analysis of visco-elastically coupled Boron Nitride nano-tube reinforced composite micro-tubes conveying viscous fluid

Computational Materials Science, Volume 96, Part B, January 2015, Pages 448-458

Abstract: In the present research, nonlinear vibration in a coupled system of Boron-Nitride nano-tube reinforced composite (BNNTRC) micro-tubes conveying viscous fluid is studied. Single-walled Boron-Nitride nano-tubes (SWBNNTs) are arranged in a longitudinal direction inside Poly-vinylidene fluoride (PVDF) matrix. Damping and shearing effects of surrounded medium are taken into account by visco-Pasternak model. Based on piezoelectric fiber reinforced composite (PFRC) theory, properties of smart coupled BNNTRC micro-tubes are obtained. To enhance the accuracy of results, strain gradient theory is developed in cylindrical shell model, and the motion equations as well as the boundary conditions are derived using Hamilton’s principle. Considering slip flow regime, the effects of various parameters such as Knudsen number, volume fraction and orientation angle of fibers, temperature change, viscosity and density of fluid on stability of coupled BNNTRC micro-tubes are investigated. Results indicate that stability of smart composite system is strongly dependent on orientation angle and volume percent of BNNTs. Results of this investigation can be applied for optimum design of shell and tube heat exchangers in micro scale.