Electrospray on superhydrophobic nozzles treated with argon and oxygen plasma

We report on a simple process to fabricate electrohydrodynamic spraying devices with superhydrophobic nozzles. These devices are useful, among other things, in mass spectrometry and printing technology. The superhydrophobic nozzle is created by roughening the surface of the polyfluorotetraethylene (PFTE) by argon and oxygen plasma treatment. We have developed a polymer-based electrospray device with a flat, superhydrophobic nozzle capable of maintaining a high contact angle and stable jetting

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

EXPERIMENTAL AND THEORETICAL STUDY OF THE CONE-JET FOR ELECTROSPRAY

ABSTRACT The interference effect on an array of electrospray emitters is analytically and experimentally investigated. An analytical model is presented to predict the behavior of the operating voltage with respect to emitter spacing in an array of emitters. The basic idea of these models is to superimpose the electric potential of individual emitters together in an array of emitters. If only one of the emitters operates and no liquid is supplied through the neighboring emitters, the potential required to form a stable cone-jet generally increases as the emitters move closer to each other due to electrical shielding. However, at very close spacing the required potential decreases. If all the emitters operate simultaneously, the operating voltage required for cone-jet spraying increases as the emitter spacing decreases; furthermore, there is no decrease in potential when the spacing is very close. The results of the analytical electrostatic interference model agree well with the experimental data

Numerical study of homogeneous nanodroplet growth

10.1016/j.jcis.2014.09.066Journal of Colloid and Interface Science43847-5

A fluid model of pulsed direct current planar magnetron discharge

Abstract We simulated a pulsed direct current (DC) planar magnetron discharge using fluid model, solving for species continuity, momentum, and energy transfer equations, coupled with Poisson equation and Lorentz force for electromagnetism. Based on a validated DC magnetron model, an asymmetric bipolar potential waveform is applied at the cathode at 50–200 kHz frequency and 50–80% duty cycle. Our results show that pulsing leads to increased electron density and electron temperature, but decreased deposition rate over non-pulsed DC magnetron, trends consistent with those reported by experimental studies. Increasing pulse frequency increases electron temperature but reduces the electron density and deposition rate, whereas increasing duty cycle decreases both electron temperature and density but increases deposition rate. We found that the time-averaged electron density scales inversely with the frequency, and time-averaged discharge voltage magnitude scales with the duty cycle. Our results are readily applicable to modulated pulse power magnetron sputtering and can be extended to alternating current (AC) reactive sputtering processes

IMECE2008-68203 FABRICATION AND TEST OF POLYMER-BASED ELECTROSPRAY DEVICE

ABSTRACT In this paper, interference effect between multi-nozzles has been experimentally investigated for an electrospray device. Array of nozzles is either prepared by electrically conductive stainless steel capillaries and by electrically dielectric nozzle array fabricated using polymer material. The result shows that polymer-based device may reduce or avoid the interference effect when the spacing distance between nozzles is optimized. For a conductive electrospray array, the end effect, which is able to deflect conejets through the outer nozzles of the array due to asymmetric electric field and repulsive forces between adjacent conductive nozzles and the menisi, can be eliminated by using two dry nozzles mounted at the boundary. However, for a polymer-based device, the end effect can be avoided without using extra dry nozzles. In order to eliminate this end effect, a novel ten-nozzle Polymethyl Methacrylate (PMMA)-based electrospray, with inner and outer diameters of 300µm and 500µm, respectively, has been successfully fabricated and evaluated. The performce of the multi-nozzle array device is analysed by measuring the current of the charged droplets through a novel ten nozzles of the polymer-based electrospray device

Growth and wetting of water droplet condensed between micron-sized particles and substrate

We study heterogeneous condensation growth of water droplets on micron-sized particles resting on a level substrate. Through numerical simulations on equilibrium droplet profiles, we find multiple wetting states towards complete wetting of the particle. Specifically, a partially wetting droplet could undergo a spontaneous transition to complete wetting during condensation growth, for contact angles above a threshold minimum. In addition, we find a competitive wetting behavior between the particle and the substrate, and interestingly, a reversal of the wetting dependence on contact angles during late stages of droplet growth. Using quasi-steady assumption, we simulate a growing droplet under a constant condensation flux, and the results are in good agreement with our experimental observations. As a geometric approximation for particle clusters, we propose and validate a pancake model, and with it, show that a particle cluster has greater wetting tendency compared to a single particle. Together, our results indicate a strong interplay between contact angle, capillarity and geometry during condensation growth.NRF (Natl Research Foundation, S’pore)Published versio

Prediction and optimization of processing parameters in wire and arc-based additively manufacturing of 316L stainless steel

Wire and arc-based additively manufacturing (WAAM) is a potential metallic additively manufacturing (AM) technologies for producing large-size metallic components. 316L is one of the most common stainless-steel grades used in WAAM. However, most of previous studies normally adopted process parameters for the WAAM process based on recommendations of welding wire manufacturers for traditional welding processes. In this article, we focus on predicting and optimizing process parameters for the WAAM process of 316L stainless steel. The experiment was designed by using Taguchi method and L16 orthogonal array. Three parameters, consisting of voltage (U), welding current (I), and travel speed (v), were considered as the input variables, and the responses are four geometrical characteristics of single weld beads, including width, height, penetration, and dilution of weld beads (WWB, HWB, PWB, and DWB, respectively). The effects of each input variable on the responses were determined through analysis of variance (ANOVA). The optimal process parameters were identified by using GRA (grey-relational analysis) and TOPSIS (techniques for order-preferences by similarity-to-ideal solution) methods. The obtained results show that the travel speed has the most important effect on WWB and HWB, while the voltage has the highest impact on PWB and DWD. Both GRA and TOPSIS methods give the same optimum process parameters, namely U = 22 V, I = 110 A, and v = 0.3 m/min, which are validated by confirmation experiments. The predicted models of WWB, HWB, PWB, and DWB were also demonstrated to be adequate for selecting the process parameters in specific applications