Water Drop Volume Research Articles

Double Emulsions Stabilized by PGPR and Arabic Gum as Capsules: The Surprising Stabilizing Role of Inner Droplets.

The encapsulation efficiency and stability over time of either vitamin B12, a model hydrophilic drug, or an aqueous suspension of Cydia pomonella granulovirus (CpGV), which is a biopesticide, using a water-in-sunflower oil-in-water (W1/O/W2) double emulsion, are studied. Two antagonistic stabilizers are used to prepare the double emulsion: the mainly lipophilic polyglycerol polyricinoleate (PGPR) and the mainly hydrophilic polysaccharide Arabic gum (AG). Combining ultraviolet-visible (UV-visible) titration, rheology, and oil globule size measurement allows assessing drug release, emulsion elasticity, and globule evolution as a function of time. A stability diagram is plotted as a function of two determining parameters: the nonadsorbed PGPR concentration in the oil and the inner water droplet fraction. To understand the presence of the nonstability domains, the influence of the two identified parameters on the outermost interfacial tension is examined. Surprisingly, the inner water drop volume fraction exhibits a stabilizing phenomenon that is discussed in terms of interfacial shielding to PGPR adsorption.

Adaptation of application of drop area method to characterize hydrophobicity of materials

The drop area can characterize hydrophobicity of materials. To improve accuracy of the drop area method, a large number of drop profiles with different contact angles, drop volumes and liquid parameters (Δρ/γ) are numerically generated. Based on the generated profiles, the influences of contact angle, drop volume and liquid parameter on the drop area and its sensitivity dS/dθ are systematically investigated. The results reveal that the sensitivity of the drop area method reduces with increasing contact angle, and increases with increasing drop volume and liquid parameter. The drop area method is particularly suitable for application in the case with small contact angle and at the same time, the drop volume and liquid parameter should be not so low. The relationship between water drop area and contact angle at some common drop volumes is obtained by numerical calculation. The concept of critical contact angle for the drop area method is proposed and the values of critical contact angle corresponding to different water drop volumes are presented. And it can be used to determine whether the drop area method or the static contact angle method should be selected. Finally, the contact angle method and the drop area method are used to measure hydrophobicity of glass and silicone rubber with different water drop volumes. The results validate the above analysis and at the same time it is consistent with the corresponding numerical calculation. This work is helpful to improve the accuracy in the drop area method and to generalize the use of it.

Vapor Lubrication for Reducing Water and Ice Adhesion on Poly(dimethylsiloxane) Brushes

Fast removal of small water drops from surfaces is a challenging issue in heat transfer, water collection, or anti-icing. Poly(dimethylsiloxane) (PDMS) brushes show good prospects to reach this goal because of their low adhesion to liquids. To further reduce adhesion of water drops, here, the surface to the vapor of organic solvents such as toluene or n-hexane is exposed. In the presence of such vapors, water drops slide at lower tilt angle and move faster. This is mainly caused by the physisorption of vapor and swelling of the PDMS brushes, which serves as a lubricating layer. Enhanced by the toluene vapor lubrication, the limit departure volume of water drop on PDMS brushes decreases by one order of magnitude compared to that in air. As a result, the water harvesting efficiency in toluene vapor increases by 65%. Benefits of vapor lubrication are further demonstrated for de-icing: driven by gravity, frozen water drops slide down the vertical PDMS brush surface in the presence of vapor.

A Multitasking Flexible Sensor via Reservoir Computing.

Natural disasters are reported globally, and one source of severe damage to cities is flooding caused by locally heavy rain. Sharing of local weather information can save lives. However, it is difficult to collect local weather information in real-time because such data collection requires bulky, expensive sensors. For local, real-time monitoring of heavy rain and wind, a sensor system should be simple and low-cost so that it can be attached to a variety of surfaces, including roofs, vehicles, and umbrellas. To develop simple, low-cost multitasking sensors located on nonplanar surfaces, a flexible rain sensor to monitor waterdrop volume and wind velocity is devised. To monitor both simultaneously, a laser-induced graphene-based superhydrophobic conductive film is introduced. Using the superhydrophobic surface, water dynamics are measured when waterdrops collide with the sensor surface, and obtained time-series data are processed using "reservoir computing" to extract the volume and velocity from a single sensor as multitasking electronics. As a proof-of-concept, it is shown that the sensor measures continuous, long-term volume and wind-change dynamics. The results demonstrate feasibility of multitasking electronics with reservoir computing to reduce sensor integration complexity with low power consumption for both sensor and signal processing.

How Swelling, Cross-Linking, and Aging Affect Drop Pinning on Lubricant-Infused, Low Modulus Elastomers

Soft, slippery surfaces have gained increasing attention because of their wide range of potential applications, for example in biomaterials, self-cleaning, antifouling, liquid collection, and more. One approach to prepare a soft, slippery surface is by swelling a cross-linked polymer network with a lubricant. However, an understanding of how swelling and cross-linking relate to slippery properties is still underdeveloped for low modulus elastomers. We study when a water drop sticks or slides on a vertical, silicone oil-swollen polydimethylsiloxane (PDMS) elastomer as a function of the degree of cross-linking and the degree of swelling. Our results indicate that the critical water drop volume required for sliding is strongly controlled by the degree of swelling; higher swelling leads to lower critical drop volumes. In addition, we demonstrate that highly swollen surfaces, and not lightly swollen surfaces, recover their slippery behavior during an aging process after they are rinsed with water. This is likely associated with regeneration of an oil-layer on the surface coming from the bulk substrate, illustrating the durability of lubricant-swollen elastomers for practical uses.

Enhancing hydrophobic properties of ZnO structures using gold coatings

The effect of enhancement the hydrophobic properties of the ensemble of micro- and nanostructures ZnO as a result of coating with gold was discovered. For the first time, it has been shown that coating the ensemble with a micro- and nanoparticle ZnO layer of gold leads to a sharp increase in the wetting edge angle from 145 to 168o (water drop volume 5 mm3) and a decrease in the hydrophobicity/hydrophilicity transition time under ultraviolet irradiation. Keywords: ZnO, gold, superhydrophobic. Keywords: ZnO, gold, superhydrophobic

Усиление гидрофобных свойств структур ZnO золотым покрытием

The effect of enhancement the hydrophobic properties of the ensemble of micro- and nanostructures ZnO as a result of coating with gold was discovered. For the first time, it has been shown that coating the ensemble with a micro- and nanoparticle ZnO layer of gold leads to a sharp increase in the wetting edge angle from 145 to 168 ° (water drop volume 5 mm3) and a decrease in the hydrophobicity/hydrophilicity transition time under ultraviolet irradiation. Keywords: ZnO, gold, superhydrophobic.

Wicking and Drying Behavior of Knitted Cotton Fabrics under Modified Water Drop Test

ABSTRACT Both face and back sides of cotton weft-knitted fabrics in five knitting structures (plain, rib, interlock, single pique, and double pique) were investigated based on modified water drop test (methods I and II) in terms of water diffusion time. The water drop height was raised from 1 cm to 20 cm and water drop volume was increase from 0.1 mL to 0.5 mL. The water diffusion time greatly decreased with the variation in water drop height from 0 to 15 cm. Water diffusion time was also influenced by water volume at 0.1–0.2 mL for the different structures and surfaces. It was found that the structures behaved differently, and two surfaces of fabric were capable of asymmetric water absorption property. The face side of single pique and the back side double pique had better water diffusion property. Besides, vertical wicking rate and the drying rate (methods I and II) were also conducted to evaluate the different structures. Although the plain structure was widely used for inner garments in the market, the interlock fabric was recommended in nonsweating conditions due to its poor water spreading and better drying ability, while the single-pique fabric was recommended in heavy sweating conditions due to its better water absorption ratio and faster drying rate.

Static contact angle versus volume of distilled water drop on micro patterned surfaces

Static contact angle was determined experimentally in the condition of wetting of polished and laser patterned surfaces of stainless steel substrates by distilled water drops with different volumes. In contrast with polished surface, the contact angle was found to depend on drop volume on micro patterned surfaces. In addition, the enhancement of both hydrophilic and hydrophobic properties was observed on laser patterned surfaces.

Puddle jumping: Spontaneous ejection of large liquid droplets from hydrophobic surfaces during drop tower tests

Large droplets and puddles jump spontaneously from sufficiently hydrophobic surfaces during routine drop tower tests. The simple low-cost passive mechanism can in turn be used as an experimental device to investigate dynamic droplet phenomena for drops up to 104 times larger than their normal terrestrial counterparts. We provide and/or confirm quick and qualitative design guides for such “drop shooters” as employed in drop tower tests including relationships to predict droplet ejection durations and velocities as functions of drop volume, surface texture, surface contour, wettability pattern, and fluid properties including contact angle. The latter is determined via profile image comparisons with numerical equilibrium interface computations. Water drop volumes of 0.04–400 ml at ejection speeds of −0.007–0.12 m/s are demonstrated herein. A sample application of the drop jump method is made to the classic problem of low-gravity phase change heat transfer for large impinging drops. Many other candidate problems might be identified by the reader.

Experimental investigation of liquid drop evaporation on a heated solid surface

Evaporation of a water drop was studied experimentally at a temperature difference between the solid surface and surrounding atmosphere from 30 to 60 °C. The studies were performed on the substrates with micro- and nanocoatings with different wettability. The features of evaporation were studied for the pinned, partially pinned, and depinned three-phase contact line (solid-liquid−gas interface). It is shown that with a decrease in the water drop volume, the specific evaporation rate (mass flow per unit of surface area) increases, particularly at the last stage of evaporation.

Automatic static contact angle algorithm for blurry drop images and its application in hydrophobicity measurement for insulating materials

To improve the accuracy of the static contact angle evaluation for the blurry drop images, a large number of water drop images are numerically generated or acquired by the contact angle instrument/digital camera. Based on these images, the applicability of the circle Hough transformation and circle fitting algorithms is systematically investigated and compared. The results reveal that the least-squares circle fitting algorithm is particularly suitable for the clear drop images, such as the images acquired by the contact angle instrument. The circle Hough transformation is particularly suitable for the blurry drop images, such as the images acquired by the digital camera. The influence of the contact angle on the contact angle error by the circle Hough transformation is investigated. The critical contact angle values corresponding to various water drop volumes are given, which can be used to improve the accuracy of the static contact angle measurement for the blurry drop images. A modified Hough transformation based on the critical contact angle is proposed. The modified Hough transformation is verified by the static contact angle measurements of different insulating materials. The study proposes a comparatively effective algorithm for automatic and accurate static contact angle measurement of the blurry drop images.

Simultaneous Determination of Environmental Contaminants with Different Volatilities in Tap Water Samples Using a New Approach to Single-Drop Microextraction Procedure

A new single-drop microextraction approach is proposed for the extraction of compounds with a wide range of volatilities from tap water samples with separation/detection by gas chromatographymass spectrometry. This new microextraction mode is called direct immersion-headspace-single drop microextraction (DI-HS-SDME). Trihalomethanes (THMs), hydrocarbons with low molecular weight (benzene, ethyl benzene and xylenes) and polycyclic aromatic hydrocarbons (PAHs) were the model compounds. Ten milliliters of tap water samples and drop volume of 1.5 µL of 1-octanol were used. The optimal condition for DI-HS-SDME mode was 80 min of total extraction time (48 min at 40 °C in DI-SDME mode and 32 min at 12 °C in HS-SDME mode) and the addition of 1.2 g of NaCl. The analytical figures of merit were evaluated, the limits of detection ranged from 0.03 µg L-1 for o-xylene and ethyl benzene to 6 µg L-1 for THMs. The proposed method represents a promising alternative for the analysis of aqueous matrices which contain compounds with very different ranges of volatility.

An algorithm for selecting the most accurate protocol for contact angle measurement by drop shape analysis.

In this study, an error analysis is performed to study real water drop images and the corresponding numerically generated water drop profiles for three widely used static contact angle algorithms: the circle- and ellipse-fitting algorithms and the axisymmetric drop shape analysis-profile (ADSA-P) algorithm. The results demonstrate the accuracy of the numerically generated drop profiles based on the Laplace equation. A significant number of water drop profiles with different volumes, contact angles, and noise levels are generated, and the influences of the three factors on the accuracies of the three algorithms are systematically investigated. The results reveal that the above-mentioned three algorithms are complementary. In fact, the circle- and ellipse-fitting algorithms show low errors and are highly resistant to noise for water drops with small/medium volumes and contact angles, while for water drop with large volumes and contact angles just the ADSA-P algorithm can meet accuracy requirement. However, this algorithm introduces significant errors in the case of small volumes and contact angles because of its high sensitivity to noise. The critical water drop volumes of the circle- and ellipse-fitting algorithms corresponding to a certain contact angle error are obtained through a significant amount of computation. To improve the precision of the static contact angle measurement, a more accurate algorithm based on a combination of the three algorithms is proposed. Following a systematic investigation, the algorithm selection rule is described in detail, while maintaining the advantages of the three algorithms and overcoming their deficiencies. In general, static contact angles over the entire hydrophobicity range can be accurately evaluated using the proposed algorithm. The ease of erroneous judgment in static contact angle measurements is avoided. The proposed algorithm is validated by a static contact angle evaluation of real and numerically generated water drop images with different hydrophobicity values and volumes.

A high accurate static contact angle algorithm based on Hough transformation

The static contact angle for blurry drop images is more intricate to obtain. To improve the accuracy of the Hough transformation for the static contact angle calculation, the water drop images with different volumes are generated by the Laplace equation, and the influence of the volume on the accuracy of the Hough transformation is analyzed. The results reveal that the circle Hough transformation is particularly well suited to the cases with small drop volume. At the same time, the critical water drop volume value corresponding to a contact angle error of 3° is given, a modified Hough transformation algorithm in conjunction with the critical water drop volume is proposed, and at the same time, the accuracy of the static contact angle calculation for blurry water drop images is significantly improved. The proposed algorithm is a powerful approach to estimate the static contact angle for blurry water drop images.

The Flashover Phenomena due to Water Drops on Insulating Surface under DC Electric Field

This paper presents the flashover between the electrodes conducted the current by the water drop on insulating surfaces. It causes ageing to the insulator and leads to deterioration when the insulator is used for over years. In the experiments, epoxy resin with the water drop is tested by using direct current until flashover of 70 kV. Besides that, the effect of the water volume, the number of the water drop and the water types - tap and aqua water on flashover are investigated. The flashover of tap water grows faster when increases the volume of water drop. The flashover of aqua water does not depend on the volume of water drop. The deformation and elongate of water drop is in the direction of electric field line. The results lead to protect the damage of insulator caused by the humidity and the loss of their efficiency insulators.

Static contact angle algorithm selection for superhydrophobic surface hydrophobicity detection

The static contact angle calculation for superhydrophobic surfaces is systematically investigated. The water drop profiles with different volumes, contact angles, rotational angles and apex coordinates are numerically generated based on the Laplace equation. Thereafter, the goniometry, θ/2 method, circle and ellipse fitting algorithms and an improved axisymmetric drop shape analysis-profile (ADSA-P) algorithm are used to calculate the static contact angle. The results reveal that the contact angle errors by the θ/2 method, circle and ellipse fitting algorithms increase with the drop volume/contact angle. The goniometry will introduce significant error. The ADSA-P algorithm can accurately obtain the contact angles (error < 0.3°) for the drop profiles regardless of the water drop volume, contact angle, rotational angle and apex coordinate. The ADSA-P algorithm should be selected to calculate the static contact angles for the superhydrophobic surfaces. Static contact angle measurements of the superhydrophobic surfaces validate the aforementioned analysis.

The effect of drop size on contact angle measurements of superhydrophobic surfaces

In this study, the effect of drop volume on contact angle (CA) values and also on the applicability of the Cassie–Baxter equation is experimentally investigated. To do this, dimethyldichlorosilane (DMDCS) coated different sized square pillar surfaces with varying fCBs(geo) values were used. Varying water drop volumes between 0.5 μl and 19 μl were used to measure CA's on square pillar surfaces with different pattern sizes changing from 8 μm to 40 μm. It was found that experimental CA values remained constant for each drop volume, indicating that increase or decrease in drop volume had no significant effect on experimentally measured CA values of square pillar surfaces with varying pattern sizes and fCBs(geo) values. When the relationship between the applicability of the Cassie–Baxter equation and the drop volume was investigated, it was also found that variation in volume of the drop did not cause a significant change in deviations between the theory and the experiments. ΔθCB values remained almost constant for all samples at varying drop volumes.

An inclined plane based dynamic contact angle algorithm and its validity in application of hydrophobicity measurement for insulating materials

The dynamic contact angle is an important method to evaluate the hydrophobicity of material. To improve the accuracy of the dynamic contact angle measurement, the validity of the ellipse fitting algorithm in application of the dynamic contact angle measurement is analyzed. Water drop profiles with different volumes, contact angles and inclination angles are numerically generated based on the Laplace equation and finite difference method and at the same time, the ellipse fitting algorithm is used to calculate the dynamic contact angle. The results reveal that the significant error (/sp Gt/7°) in contact angle may be difficult to find. The dynamic contact angle error increases with the water drop volume. The ellipse fitting algorithm is not suitable for the case of too small or large contact angle. The critical water drop volumes corresponding to an error of 3° are given and the accuracy of the dynamic contact angle measurement is improved by using the volume. The results are verified by the experiments.

A static contact angle algorithm and its application to hydrophobicity measurement in silicone rubber corona aging test

To improve the accuracy of the static contact angle measurement for the corona aged silicone rubber, a static contact angle algorithm based on the least-squares circle fitting is presented, and the least-squares model, the optimization algorithm, the determination of initial values and the convergence criterion are introduced in a systematic way and at the same time the best selections are given by the systematical comparison. With regards to the numerically generated water drop profiles and the water drop images of the corona aged silicone rubber, the accuracy and the computation time of the goniometry, the θ/2 method, the circle fitting algorithm and the ADSA-P (axisymmetric drop shape analysis-profile) algorithm are analyzed and compared. The influence of the water drop volume/contact angle/profile point number on the accuracy of the circle fitting algorithm is analyzed. The results reveal that the contact angle errors increase with the water drop volume/contact angle/noise. The goniometry has the characteristics of relative low accuracy, expensive computation and large workload. The computed result of the circle fitting algorithm is very close to that of the θ/2 method, and both the two methods have relative less computation time. In the meantime, the fitted water drop edges can be obtained by the circle fitting algorithm, which can be taken as an indicator of the computation accuracy, while the θ/2 method cannot give such indicator. The ADSA-P algorithm has high accuracy and high computational complexity, and is very easy to be interfered by the noise. Therefore, it is not suited to the case of small contact angle and volume, and high interference. The circle fitting algorithm has less computation time, and is intrinsically resistant to noise. Therefore, for the case of small contact angle and volume, not the ADSA-P algorithm but the circle fitting algorithm should be selected. Therefore, the circle fitting algorithm is selected to measure the static contact angle of the corona aged silicone rubber. The critical water drop volumes and the critical contact angles of different liquids are given, which can be guaranteed for high accuracy of the static contact angle measurement.