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ABSTRACT: Superhydrophobic surfaces based on polydimethyl siloxane (PDMS) were fabricated using a 50:50 PDMS-poly(ethylene glycol) (PEG) blend. PDMS was mixed with PEG, and incomplete phase separation yielded a hierarchic structure. The phase-separated mixture was annealed at a temperature close to the crystallization temperature of the PEG. The PEG crystals were formed isothermally at the PDMS/PEG interface, leading to an engineered surface with PDMS spherulites. The resulting roughness of the surface was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The PDMS spherulites, a few micrometers in diameter observed from SEM images, were found to have an undulated (rippled) surface with nanometer-sized features. The combination of micrometer- and nanometer-sized surface features created a fractal surface and increased the water contact angle (WCA) of PDMS more than 60°, resulting in a superhydrophobic PDMS surface with WCA of >160°. The active surface layer for the superhydrophobicity was approximately 100 μm thick, illustrating that the material had bulk superhydrophobicity compared to conventional fluorocarbon or fluorinated coated rough surfaces. Theoretical analysis of the fractal surface indicates that the constructed surface has a fractal dimension of 2.5, which corresponds to the Apollonian sphere packing.
Langmuir 02/2011; · 4.19 Impact Factor
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ABSTRACT: A polymeric nanocomposite system (nanodielectric) was fabricated, and its mechanical properties were determined. The fabricated nanocomposite was composed of low concentrations of monodispersed titanium dioxide (TiO2) nanoparticles and an epoxy resin specially designed for cryogenic applications. The monodispersed TiO2 nanoparticles were synthesized in an aqueous solution of titanium chloride and polyethylene glycol and subsequently dispersed in a commercial-grade epoxy resin (Araldite® 5808). Nanocomposite thin sheets were prepared at several weight fractions of TiO2. The morphology of the composites, determined by transmission electron microscopy, showed that the nanoparticles aggregated to form particle clusters. The influence of thermal processing and the effect of filler dispersion on the structure–property relationships were identified by differential scanning calorimetry and dynamic mechanical analysis at a broad range of temperatures. The effect of the aggregates on the electrical insulation properties was determined by dielectric breakdown measurements. The optical properties of the nanocomposites and their potential use as filters in the ultraviolet–visible (UV–vis) range were determined by UV–vis spectroscopy. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers
Polymer Engineering and Science 08/2010; 51(1):87 - 93. · 1.30 Impact Factor
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ABSTRACT: Physical properties of a nanodielectric composed of in situ synthesized titanium dioxide (TiO2) nanoparticles ( ≤ 5 nm in diameter) and a cryogenic resin are reported. The dielectric losses were reduced by a factor of 2 in the nanocomposite, indicating that the presence of small TiO2 nanoparticles restricted the mobility of the polymer chains. Dielectric breakdown data of the nanodielectric was distributed over a narrower range than that of the unfilled resin. The nanodielectric had 1.56 times higher 1% breakdown probability than the resin, yielding 0.64 times thinner insulation thickness for the same voltage level, which is beneficial in high voltage engineering.
Applied Physics Letters 04/2010; 96(15):152903-152903-3. · 3.84 Impact Factor
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ABSTRACT: In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed
magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that
the matrix polymeric material is confined in approximately 100nm size cages between particle clusters. The particle clusters
are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation
and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide
particles. The dielectric breakdown measurements performed at 77K showed that these nanodielectrics are potentially useful
as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties
of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity
values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have
low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a
low dielectric permittivity surfactant.
Applied Physics A 02/2009; 94(4):843-852. · 1.63 Impact Factor
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ABSTRACT: In this paper, we report the dielectric breakdown properties of a nanocomposite, a potential electrical insulation material for cryogenic high voltage applications. The material is composed of a high molecular weight polyvinyl alcohol and nanosized in situ synthesized titanate particles. The dielectric breakdown strengths of the filled material samples, measured in liquid nitrogen, indicate a significant increase in their strengths as compared to unfilled polyvinyl alcohol. We conclude that nanometre-sized particles can be adopted as a voltage stabilization additive.
Nanotechnology 07/2007; 18(32):325704. · 3.98 Impact Factor
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ABSTRACT: We investigate the electrical properties of composite materials prepared as nano- and sub-micron-scale metal-oxide particles embedded in a commercial resin. The filler particles are barium titanate and calcium copper titanate. The physical and structural characteristics of the constituents and the fabricated composites are reported. Electrical characterization of the composite samples is performed using time- and frequency-domain dielectric spectroscopy techniques. The electrical breakdown strength of samples with nano- and sub-micron-sized particles have better electrical insulation properties than the unfilled resin.
Nanotechnology 12/2006; 18(2):025703. · 3.98 Impact Factor
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ABSTRACT: In this paper, we investigate the dielectric breakdown data of some insulating materials and focus on the applicability of the two- and three-parameter Weibull distributions. A new distribution function is also proposed. In order to assess the model distribution's trustworthiness, we employ the Monte Carlo technique and, randomly selecting data-subsets from the whole dielectric breakdown data, determine whether the selected probability functions accurately describe the breakdown data. The utility and strength of the proposed expression are illustrated distinctly by the numerical procedure. The proposed expression is shown to be a valuable alternative to the Weibull ones.
Journal of Physics D Applied Physics 09/2006; 39(19):4257. · 2.54 Impact Factor
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04/2002;
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04/2002;
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ABSTRACT: Electron attachment to trichlorotrifluoroethane (1, 1, 2-) was investigated in buffer gases of and Ar using a high-temperature electron swarm apparatus. The negative ion intensity was also measured as a function of electron energy using an electron beam apparatus. The electron attachment rate constant, , was measured in the mean electron energy range, , 0.043 to 4.7 eV and over a temperature, T, range 300 to 700 K in the electron swarm experiments. The electron attachment rate constant was found to first increase slightly with increasing temperature and subsequently decrease for K. Our room-temperature electron beam study showed that 1, 1, 2- attaches electrons predominantly via dissociative negative ion states and revealed that the electron attachment cross section exhibits three main peaks: one at eV producing , a second one at eV due to and a third one at eV also producing . The electron attachment cross sections obtained using an electron swarm-unfolding technique show that the peak at eV observed in the electron beam study is actually composed of three peaks; one at eV and two more at higher electron energies but below 1.5 eV.
Journal of Physics D Applied Physics 12/1998; 30(18):2596. · 2.54 Impact Factor
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Isidor Sauers
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ABSTRACT: The yields of SOF4, SO2F2, SOF2, and SO2 have been measured as a function of O2 content in SF6/O2 mixtures, following spark discharges. All experiments were made at a spark energy of 8.7 J/spark, a total pressure of 133 kPa, and for O2 additions of 0, 1, 2, 5, 10, and 20% to SF6. Even for the case of no added O2, trace amounts of O2 and H2O result in the formation of the above by-products. However, addition of O2 significantly increases the yields of SOF4 and SO2F2, while SOF2 is only slightly affected. The net yields for SOF4 and SO2F2 formation range from 0.1810–9 and 0.6410–10 molJ–1, respectively, at 1% O2 content to 10.4510–9 and 7.1510–10 molJ–1, respectively, at 20% O2 content. The mechanism for SOF4 production appears to involve SF4, an important initial product of SF6, as a precursor. Comparison of the SOF4 and SO2F2 yield from spark discharges (arc and corona) shows that the yields from other discharges (arc and corona) shows that the yields can vary by at least three orders of magnitude, depending on the type of discharge and on other discharge parameters.
Plasma Chemistry and Plasma Processing 05/1988; 8(2):247-262. · 1.60 Impact Factor
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ABSTRACT: The field of nanodielectrics has had a significant impact on voltage endurance characteristics of electrical insulation. Improved
time-to-breakdown behavior, resulting in reduced aging of insulation, and enhanced thermal stability are of considerable importance
in industrial applications. This chapter discusses several specific aspects of nanodielectrics and their role in the future
of electrical insulation and dielectric sciences.
01/1970: pages 321-338;
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Isidor Sauers
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ABSTRACT: We have measured the response of gold-coated silicon nitride microcantilevers to 2-mercaptoethanol (HS–CH2–CH2–OH) vapors and found that they respond rather sensitively to 2-mercaptoethanol vapors. Such microcantilevers can be used to develop sensitive micromechanical chemical sensors for detecting sulfur-containing compounds. Microcantilevers with a gold coating on one side respond to adsorption of molecules by changes in their resonance frequency and/or bending. The bending induced from adsorption of 2-mercaptoethanol molecules on microcantilevers is at least an order of magnitude more sensitive than any corresponding resonance frequency changes resulting from mass loading. In the present studies, we used the adsorption-induced bending and placed a lower limit in the minimum detectable concentration of mercaptan vapor at <50 parts per billion (ppb).
Sensors and Actuators B: Chemical.
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ABSTRACT: Improvements in superconductor and cryogenic technologies enable novel power apparatus, e.g., cables, transformers, fault current limiters, generators, it etc., with better device characteristics than their conventional counterparts. In these applications electrical insulation materials play an important role in system weight, footprint (size), and voltage level. The trend in the electrical insulation material selection has been to adapt or to employ conventional insulation materials to these new systems. However, at low temperatures, thermal contraction and loss of mechanical strength in many materials make them unsuitable for superconducting power applications. In this paper, a widely used commercial material was characterized as a potential cryogenic dielectric. The material is used in “oven bags” which is a heat-resistant polyamide (nylon) used in cooking (produced by Reynolds®, Richmond, VA, USA). It is first characterized by Fourier transform infrared and X-ray diffraction techniques and determined to be composed of polyamide 66 (PA66) polymer. Secondly the complex dielectric permittivity and dielectric breakdown strength of the PA66 films are investigated. The dielectric data are then compared with data reported in the literature. A comparison of dielectric strength with a widely used high-temperature superconductor electrical insulation material, polypropylene-laminated paper (PPLP™ a product of Sumitomo Electric Industries, Japan), is provided. It is observed that the statistical analysis of the PA66 films yields 1% failure probability at ; this value is approximately higher than PPLP™. Comparison of the mechanical properties of PA and PPLP™ indicates that PA66 has low storage and loss moduli than PPLP™. It is concluded that PA66 may be a good candidate for cryogenic applications. Finally, a summary of dielectric properties of some of the commercial tape insulation materials and various polymers is also provided.
Cryogenics.
