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Esmeryan K.D.,Georgi Nadjakov Institute of Solid State Physics | McHale G.,Northumbria University | Trabi C.L.,Northumbria University | Geraldi N.R.,Nottingham Trent University | Newton M.I.,Nottingham Trent University
Journal of Physics D: Applied Physics | Year: 2013

The liquid phase response of quartz crystal microbalances (QCMs) with a thin coating (∼9 μm) of epoxy resin with and without a carbon nanoparticles top layer is reported. The nanoparticles convert the epoxy surface to a superhydrophobic one with a high static contact angle (∼151°- 155°) and low contact angle hysteresis (∼1°-3.7°) where droplets of water are in the suspended Cassie-Baxter state. The frequency decrease of the fully immersed QCM with the superhydrophobic surface is less than with only epoxy layer, thus indicating a decoupling of the QCM response. A wettability transition to a liquid penetrating into the surface roughness state (for droplets a high contact angle hysteresis Wenzel state) was triggered using a molarity-of-ethanol droplet test (MED) and electrowetting; the MED approach caused some surface damage. The electrowetting-induced transition caused a frequency decrease of 739 Hz at a critical voltage of ∼100 V compared to the QCM in air. This critical voltage correlates to a contact angle decrease of 26° and a high contact angle hysteresis state in droplet experiments. These experiments provide a proof-of-concept that QCMs can be used to sense wetting state transitions and not only mass attachments or changes in viscosity-density products of liquids. © 2013 IOP Publishing Ltd. Source

Prakash O.,RandD C 1 Block | Astadjov D.N.,Georgi Nadjakov Institute of Solid State Physics | Kumar P.,RandD C 1 Block | Mahakud R.,RandD C 1 Block | And 3 more authors.
Optics Communications | Year: 2013

This paper presents a first comprehensive experimental study and theoretical analysis on the effect of spatial coherence on the focusability of annular laser beams. The circular apertures of annularity 0, 0.2, 0.4, 0.6 and 0.8 were studied experimentally for the far-field intensity distributions with three different partially coherent incident visible pulsed laser beams of spatial coherence fraction of 100%, 40% and 2% of full beam cross-section. These beams were generated from a copper vapor laser with different optical resonators. The spatial coherence fraction was computed from the interferograms recorded by a reversal shear interferometer. The resulting far-field patterns of focused annular beam were found to depend very critically on the spatial coherence of the incident beam. A theoretical analysis, based on Fourier transform of partially coherent incident light with coherent function taken as J1(r)/r, was carried out. The far-field diffraction patterns were estimated numerically for the annular beams involving correlation interval and obstruction ratio. The MATLAB based mathematical process was the Fourier transformation of the product of source autocorrelation function and correlation function across the aperture. Experimental and theoretical results are in good agreement. © 2012 Elsevier B.V. All rights reserved. Source

Esmeryan K.D.,Virginia Commonwealth University | Esmeryan K.D.,Georgi Nadjakov Institute of Solid State Physics | Castano C.E.,Virginia Commonwealth University | Bressler A.H.,Virginia Commonwealth University | And 2 more authors.
Applied Surface Science | Year: 2016

The fabrication of superhydrophobic coatings using a candle flame or rapeseed oil has become very attractive as a novel approach for synthesis of water repellent surfaces. Here, we report an improved, simplified and time-efficient method for the preparation of robust superhydrophobic carbon soot that does not require any additional stabilizers or chemical treatment. The soot's inherent stabilization is achieved using a specially-designed cone-shaped aluminum chimney, mounted over an ignited paper-based wick immersed in a rapeseed oil. Such configuration decreases the level of oxygen during the process of combustion; altering the ratio of chemical bonds in the soot. As a result, the fractal-like network of the carbon nanoparticles is converted into dense and fused carbon chains, rigidly coupled to the substrate surface. The modified carbon coating shows thermal sustainability and retains superhydrophobicity up to ∼300 °C. Furthermore, it demonstrates a low contact angle hysteresis of 0.7-1.2° accompanied by enhanced surface adhesion and mechanical durability under random water flows. In addition, the soot's deposition rate of ∼1.5 μm/s reduces the exposure time of the substrate to heat and consequently minimizes the thermal effects, allowing the creation of superhydrophobic coatings on materials with low thermal stability (e.g. wood or polyethylene). © 2016 Elsevier B.V. All rights reserved. Source

Esmeryan K.D.,Virginia Commonwealth University | Esmeryan K.D.,Georgi Nadjakov Institute of Solid State Physics | Castano C.E.,Virginia Commonwealth University | Bressler A.H.,Virginia Commonwealth University | And 2 more authors.
RSC Advances | Year: 2016

A novel method for the flame synthesis of carbon nanoparticles with controllable fraction of amorphous, graphitic-like and diamond-like phases is reported. The structure of nanoparticles was tailored using a conical chimney with an adjustable air-inlet opening. The opening was used to manipulate the combustion of an inflamed wick soaked in rapeseed oil, establishing three distinct combustion regimes at fully-open, half-open and fully-closed opening. Each regime led to the formation of carbon coatings with diverse structure and chemical reactivity through a facile, single-step process. In particular, the fully-closed opening suppressed most of the inlet air, causing an increased fuel/oxygen ratio and decreased flame temperature. In turn, the nucleation rate of soot nanoparticles was enhanced, triggering the precipitation of some of them as diamond-like carbon (DLC). Surface characterization analyses using Raman spectroscopy, X-ray photoelectron spectroscopy and transmission electron spectroscopy confirmed this hypothesis, indicating a short-range ordered nanocrystalline structure and ∼80% sp3 bonds in the coatings deposited at fully-closed opening. Furthermore, three groups of 5 MHz Quartz Crystal Microbalances (QCMs) coated with soot and DLC, corresponding to each of the three combustion regimes, showed different frequency responses to aqueous ethanol and isopropanol solutions in the concentration range of 0-12.5 wt%. The DLC coated QCMs exhibited relatively constant frequency shift of ∼2250 Hz regardless of the chemical, while the response of soot coated counterparts was influenced by the quantity of heteroatoms in the film. Our method can be applied in chemical sensing for the development of piezoresonance liquid sensors with tunable sensitivity. © 2016 The Royal Society of Chemistry. Source

Esmeryan K.D.,Georgi Nadjakov Institute of Solid State Physics | Avramov I.D.,Georgi Nadjakov Institute of Solid State Physics | Radeva E.I.,Georgi Nadjakov Institute of Solid State Physics
Micromachines | Year: 2012

Temperature induced frequency shifts may compromise the sensor response of polymer coated acoustic wave gas-phase sensors operating in environments of variable temperature. To correct the sensor data with the temperature response of the sensor the latter must be known. This study presents and discusses temperature frequency characteristics (TFCs) of solid hexamethyldisiloxane (HMDSO) polymer coated sensor resonators using the Rayleigh surface acoustic wave (RSAW) mode on ST-cut quartz. Using a RF-plasma polymerization process, RSAW sensor resonators optimized for maximum gas sensitivity have been coated with chemosensitive HMDSO films at 4 different thicknesses: 50, 100, 150 and 250nm. Their TFCs have been measured over a (-100 to +110) °C temperature range and compared to the TFC of an uncoated device. An exponential 2,500ppm downshift of the resonant frequency and a 40K downshift of the sensor's turn-over temperature (TOT) are observed when the HMDSO thickness increases from 0 to 250nm. A partial temperature compensation effect caused by the film is also observed. A third order polynomial fit provides excellent agreement with the experimental TFC curve. The frequency downshift due to mass loading by the film, the TOT and the temperature coefficients are unambiguously related to each other. © 2012 by the authors. Source

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