1,720,991 research outputs found
Nano-Silica Filled Polystyrene: Correlating DC Breakdown Strength and Particle Agglomeration.
No full textIn the field of polymer dielectrics nano-fillers have attracted a great deal of academic interest since they potentially allow significant modifications of material properties to be made. Despite the high levels of interest, no clear picture has yet emerged because results in the literature show considerable variability. Difficulties in achieving highly uniform nano-filler dispersal are perhaps the main driving force for this variability and have also hampered the adoption of nano-fillers for industrial scale applications. In this work we correlate the results from two analysis techniques in order to deepen our understanding of the action of nano-fillers in polymer dielectrics. Nano-composites were produced with filler fractions ranging from 0 – 10 %. The filler is composed of fused silica particles with a typical size of 20 nm and the matrix material is polystyrene. Polystyrene was chosen because its amorphous matrix provides a relatively simple and uniform background on which to study the action of the nano-particles. Alternative polymers which may crystallise or exhibit lamella type structures add additional layers of complexity to the study which could obscure the effect of the nano-particles. Firstly, we show the DC breakdown strength of the composites as a function of filler fraction. Secondly, samples undergo permanganic etching and are then imaged by a Scanning Electron Microscope. The SEM images of the etched surfaces reveal, as a function of filler fraction, the degree of agglomeration that has occurred. Combining these two data sets brings new insight to the action of the nano-filler within our model system as it allows the DC breakdown strength results to be interpreted in light of the agglomeration data
A dielectric spectroscopy study of the polystyrene/nanosilica model system
No full textIn this study a simple solvent blending technique is used to produce silica/polystyrene nanocomposites. Dielectric spectroscopy is then used to measure both the real and imaginary permittivity of the samples. The nanosilica/polystyrene system is characterized over a range of different filler loadings, and additionally, as a function of temperature. To supplement this, absorbed water is used as a dielectric probe to explore molecular relaxation processes at the nanoparticle interfaces
Electrostatic adhesion of polymer particles to a foil electrode
No full textThe SPABRINK EU project requires temporary adhesion of coloured solid “ink” particles to a surface, for later recovery and reuse. This is achieved through the use of dielectrophoretic force under the control of a voltage applied to an interdigitated electrode pattern on the polymer foil. One concern is the ability to hold particles under vibration conditions. In this paper we present an experimental study of the adhesion of 50-300 µm polymer particles to an experimental interdigitated electrode structure on flexible polymer foil. Powder loss as a function of calibrated displacement and applied voltage to the electrodes are presented. This is compared with theoretical results obtained by modelling adhesion using Pohl’s equation in terms of an “adhesion factor”. Some difficulties in directly comparing experimental and modelling results are discussed
Numerical calculation of dielectrophoretic and electrostatic forces acting on micro-scale particles
No full textMuch of the current literature on dielectrophoresis (DEP) relates to micro or nano scale particles; typically in micro-fluidic type experiment geometries. In contrast, this work focusses on the application of DEP forces to larger, micro-scale particles in air. Since DEP scales with particle volume, it can apply a significant force on surprisingly large objects. When using very small particles it is often sufficient to use Pohl’s method [1] whereby the particle is considered to be spherical and where it does not interact with the externally applied electric field. For the larger particles used in this work, the spherical approximation does not necessarily hold. DEP forces are therefore calculated using the finite element method (FEM) which permits the use of arbitrary particle shapes. In this model the electric field is solved in the presence of a polarizable particle, the DEP force is then calculated using the Maxwell stress tensor method [2]. The development of this model allows the investigation of the DEP forces acting on non-spherical particles for a specific experimental electrode geometry.1
Dielectrophoretic adhesion of 50-300 µm particles under ambient atmospheric conditions
No full textThe SPABRINK EU project required temporary adhesion of coloured solid “ink” particles to form an image. We use dielectrophoretic force to attach ink particles under the field from a voltage applied to an interdigitated electrode on the image carrying surface.Finite element modeling results were compared in terms of an “adhesion factor” that included the density of particles as well as dielectric constant. In our experiments 50e300 mm alumina, silica sand and polymer particles were shown to adhere to a vertical plane electrode structure under laboratory ambient atmosphere
The direct writing and focusing of nanoparticles generated by an electrical discharge
No full textDirect writing aims to deposit materials onto substrates in localised positions. In this paper, we demonstrate a new method for direct writing of nanoparticles at ambient-air-pressure. An electrical discharge is used to generate gold nanoparticles of the order of 10 nm diameter, which are then transported and 'focused' by an electric field in air, through the process of electric field-assisted diffusion, as opposed to normal ballistic focusing since the mean free path in air is very short. This process is novel and allows for practical normal atmospheric-pressure focused deposition of nanoparticles. The focusing mechanism is capable of producing patterned arrays of deposited nanoparticles with widths that are less than 10 % of the diameter of the focusing apparatus; in the present experimental configuration, gold spots with diameters of a few tens of micrometres were achieved, with ultimate size being limited by transverse diffusion and by charged particle mutual repulsion. In this study, the process of generating nanoparticles from bulk material, transporting and focusing these particles takes place in one operation, which is a key advantage in rapid prototyping and manufacturing techniques
Dielectrophoretic adhesion of 50-300µm sand and alumina particles under ambient atmospheric conditions
No full textThere are applications that require temporary adhesion of particles to a surface, including temporary printing where the "ink" is intended to be easily recovered and subsequently reused. One possible approach is through the use of dielectrophoretic force to attach coloured solid “ink” particles under the control of a voltage applied to an electrode pattern.Dielectrophoretic theory predicts that dielectrophoretic force is proportional to particle volume. In the circumstance where this force opposes gravitational force, this makes the balance of forces on a particle insensitive to particle size. It thereby is possible to suspend surprisingly large particles using highly divergent surface fields produced by interdigitated electrodes at modest voltages. <br/
Modelling pulse compression in BBO using cascaded nonlinearity: the effects of self-steepening in quadratic media
No full textIn a χ(2) material such as BBO, third order nonlinear effects can occur efficiently via a cascaded nonlinearity where light is rapidly converted from the fundamental to the second harmonic and back again with an intensity dependant phase shift. This cascaded nonlinearity has been used to demonstrate a wide range of χ(3) effects such as soliton propagation and compression. Here we study soliton-like pulse compression in a BBO crystal of 100fs input pulses looking to see the minimum pulse duration that can be obtained. Included for the first time in a systematic study is the χ(2) self steepening term[1] which we have found plays a significant role in the pulse dynamics
The breakdown strength and localised structure of polystyrene as a function of nanosilica fill-fraction
No full textIn this work the amorphous matrix of polystyrene provides a homogenous basis into which nanosilica particles are added. Composites are made with four different types of nanosilica particles which are subsequently compared. The DC breakdown strength of the resulting nanocomposite materials is measured as a function of filler fraction with loadings between 0 and 10 %. One advantage of using a polystyrene matrix for this study is its compatibility with permanganic etching. This technique is used to remove part of the polystyrene matrix and render the configuration of the nanofiller particles within the composite amenable to examination by scanning electron microscope (SEM). The simple sample preparation protocol employed here resulted in significant nanofiller agglomeration and the DC breakdown strength was found to decrease with increasing filler fraction
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