Self‐Powered Multimodal Temperature and Force Sensor Based‐On a Liquid Droplet

Herein we report a self‐powered multimodal temperature and force sensor based on the reverse electrowetting effect and the thermogalvanic effect in a liquid droplet. The deformation of the droplet and the temperature difference across the droplet can induce an alternating pulse voltage and a direct voltage, respectively, which is easy to separate/analyze and can be utilized to sense the external force and temperature simultaneously. In addition, an integral display system that can derive information from external temperature/force concurrently is constructed. Combined with advantages of excellent sensing properties and a simple structure, the droplet sensor has promising applications in a wide range of intelligent electronics.     

Particle adsorption in evaporating droplets of polymer latex dispersions on hydrophilic and hydrophobic surfaces

Stain patterns formed by drying up of droplets of polymer latex dispersion on hydrophilic and hydrophobic surfaces were examined in light of the mechanism of particle adsorption in evaporating droplets. On hydrophilic surfaces, the volume of droplets decreased with time, keeping the initial outline of contact area, and circular stain patterns were formed after the dry-up of droplets. By the microscopic observation of particles in the droplets, it was found that a large portion of the particles were forced to adsorb on the outline of the contact area where a microscopic thin water layer was formed because of hydrophilicity of the surface. On hydrophobic surfaces, on the other hand, the contact area of droplets decreased as evaporation proceeded, while no particle was adsorbed on the surface at the early stages. The particles in the droplets started to aggregate when the concentration of particles reached a critical value, and the aggregates adsorbed on the surface forming tiny spots after the dry-up. Time evolutions of contact angle, contact area and volume of the droplets were analyzed in light of differences in the adsorption mechanisms between hydrophilic and hydrophobic surfaces. Received: 14 January 1998 Accepted: 1 May 1998     

Determination of Mercury(II) in Drinking Water by Total Reflection X-ray Fluorescence Spectrometry and Liquid–Liquid Microextraction

The total reflection X-ray fluorescence determination of mercury(II) in drinking water at concentrations of 7?×?10^?2 to 3.0?µg/L is reported. The mercury(II) preconcentration protocol includes directly suspended droplet microextraction with benzene as a molecular iodine complex. The proposed approach is highly selective. The elements Cr, Mn, Fe, Co, Ni, Zn, and Pb at concentrations up to 0.1?g/L did not interfere with the extraction of trace mercury(II). The method is characterized by high sensitivity (limit of detection of 21?ng/L) and suitable reproducibility (relative standard deviation of 0.12 for 100?ng/L). The accuracy of the results was confirmed by recovery and the method of standard addition.     

Structural analysis of <Emphasis Type="Italic">w</Emphasis>/<Emphasis Type="Italic">o</Emphasis>/<Emphasis Type="Italic">w</Emphasis> multiple emulsions by means of DSC

Summary The properties of the inner and the external aqueous phases, were studied in w/o/w multiple emulsions with light microscopic image analysis and differential scanning calorimetry (DSC). The importance of multiple emulsions lies in the presence of these aqueous phases, making them available for sustained, controlled drug delivery systems. Differentiation of these two aqueous phases, studying the effect of manufacturing technology on droplet structure, quantitative determination of phase volumes and any changes occurring during storage are essential when planning w/o/w emulsions. The present study uses microscopic observations combined with DSC measurements in order to identify the formed structure, at developmental stage in case of different components, preparation methods, and stirring rates. These tools are beneficial during manufacturing as in process controls, or to ensure product quality.     

Electrophoresis of a highly charged fluid droplet in dilute electrolyte solutions: Analytical Hückel-type solution

An analytical formula is presented here for the electrophoresis of a dielectric or perfectly conducting fluid droplet with arbitrary surface potentials suspended in a very dilute electrolyte solution. In other words, when the Debye length (κ⁻¹) is very large, or κa$\ll$1, where κ is the electrolyte strength and a stands for the droplet radius. This formula can be regarded as an extension of the famous Hückel solution valid for weakly charged rigid particles to arbitrarily charged fluid droplets. The formula reduces successfully to the ones obtained by Booth for a dielectric droplet, and Ohshima for a perfectly conducting droplet, both under Debye–Hückel approximation valid for weakly charged droplets. Moreover, the formula is valid for a gas bubble and a rigid solid particle as well. Classic results obtained by Hückel for a rigid particle are reproduced as well. We found that for a dielectric droplet, the more viscous the droplet is, the faster it moves regardless of its surface potential, contrary to the intuition based on the purely hydrodynamic consideration. For a perfectly conducting liquid droplet, on the other hand, the situation is reversed: The less viscous the droplet is, the faster it moves. The presence or absence of the spinning electric driving force tangent to the droplet surface is found to be responsible for it. As a result, an axisymmetric exterior vortex flow surrounding the droplet is always present for a dielectric liquid droplet, and never there for a conducting liquid droplet.     

PDMS表面上的液滴蒸发实验研究

利用粒子跟踪测速(particle tracking velocimetry, PTV) 技术,研究了聚二甲基硅氧烷（polydimethylsiloxane, PDMS）表面上的液滴蒸发行为.发现固液界面上的荧光微球首先向固液界面中心移动,而后发生运动反转,向三相接触线移动.其原因是由于接触线钉扎时接触线附近的蒸发通量较小,从而引起向液滴中心的流动,这种流动将微球带向液滴中心.理论分析了三相接触线的移动特征,发现其移动速度理论值与实验值在同一量级,而移动加速度的实验值较理论值偏大,造成这种偏差的原因是三相接触线处的荧光微球削弱了基底对三相接触线的钉扎作用.     

Oil-in-water emulsions stabilized by whey protein aggregates: Effect of aggregate size,pH of aggregation and emulsion pH

Oil-in-water emulsions (60% oil (w/w)) were prepared using whey protein aggregates as the sole emulsifying agent. The effects of whey protein aggregate size (the diameter between 0.92 and 10.9?µm), the pH of emulsions (4–8.6) and storage time on physical properties, droplet size, and stability of emulsions were investigated. The results indicate that increment of whey protein aggregate size caused an increase in the firmness, droplet size, and viscosity of emulsions, and also a decrease in the emulsion creaming. The emulsion viscosity, firmness, and droplet size were reduced by increasing the emulsion pH; however, the creaming process was accelerated. Viscosity, creaming, and droplet size of emulsions were increased slightly during 21 days storage at 40°C.     

XPS depth analysis of metal/polymer multilayer by vacuum electrospray droplet impact

Recently, the vacuum electrospray droplet impact (V‐EDI) was developed as a cluster ion beam source in our laboratory. In this work, V‐EDI was applied to polymers [polyimide (PI) and polycarbonate (PC)] and metal/polymer multilayer samples (Au/PI and Au/PC). We compared the etching performance of V‐EDI with that obtained by the conventional atmospheric‐pressure EDI (A‐EDI). The nonselective etching was observed for organic and also inorganic samples by V‐EDI as by A‐EDI. Etching rates for the metal and polymer analysis by V‐EDI were almost the same as those observed by A‐EDI. The interlayer components were clearly observed by V‐EDI for multilayer samples of Au and synthetic polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of the contact-line dynamics on the natural oscillations of a cylindrical droplet

The natural oscillations of a cylindrical droplet of an inviscid liquid surrounded by a different liquid and bounded in the axial direction by solid planes are studied. The motion of the contact line is described using an effective boundary condition. The dependence of the frequency and damping ratio on the capillary parameter is found. It is shown that the fundamental frequency of the translation mode vanishes beginning from a certain value of the capillary parameter. Depending on the ratio of the radial and axial dimensions of the droplet, the fundamental frequency of the axisymmetric mode and modes higher than the translation mode can vanish in a certain range of the capillary parameter. This dependence of the natural oscillation frequencies on the problem parameters allows one to determine the capillary parameter. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 5, pp. 78–86, September–October, 2007.     

The effects of coil-stretch transition behavior of polyfluorene inks on single droplet formation during inkjet printing

For drop-on-demand (DOD) inkjet printing, stable and single ink droplet formation without satellite dots is the key to improve the print quality. The formation of stable and single droplet is influenced by filament break up and the polymer chain's coil-stretch transition behavior. In this paper, the droplet formation behaviors of polyfluorene (PFO) ink at various driving voltages (V), polymer chain's coil-stretch transition mechanism and its effects on single ink droplet formation are investigated. It indicates that when 58 < V ≤ 63 V, a single and stable droplet is formed with a pulse time of 38.5 μs. At this stage, the Weissenberg number (Wi) < 0.5, the PFO molecular chain is coiled to guarantee stable and single droplets. When V > 63 V, Wi > 0.5, the PFO molecular chain is stretched because of the high hydrodynamic forces, resulting unwanted satellite droplets. When 55 < V ≤ 58 V, the droplet shrinks into the nozzle, which indicates that the kinetic energy supplied by the deformation of the piezoelectric transducer isn't enough to force the droplet to be jetted from the nozzle.