The physics of water droplets on surfaces: exploring the effects of roughness and surface chemistry

Eid, Khalid; Panth, Mohan; Sommers, Andrew D.

doi:10.1088/1361-6404/aa9cba

Cited by 36 publications

(19 citation statements)

References 38 publications

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“…The size of the testing droplet has to be adjusted prior to the measurements. The effect of droplet size on contact angle has always been an issue and appears to have a significant effect on rough surfaces (Amrei et al 2017;Eid et al 2018). In the actual study, a drop of 5 μl volume was used.…”

Section: Methodsmentioning

confidence: 99%

Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

2021

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Surface tension of solid wood surfaces affects the wettability and thus the adhesion of various adhesives and wood coatings. By measuring the contact angle of the wood, the surface tension can be calculated based on the Young-Dupré equation. Several publications have reported on contact angle measured with different test liquids, under different conditions. Results can only be compared if the test conditions are similar. While the roles of the drop volume, image shooting time etc., are widely recognized, the role of the wood surface moisture content (MC) is not evaluated in detail. In this study, the effect of wood moisture content on contact angle values, measured with distilled water and diiodomethane, on sanded birch (Betula pendula) surfaces was investigated, in order to find the relationship between them. With increasing MC from approximately 6% to 30%, increasing contact angle (decreasing surface tension) values were measured according to a logarithmic function. The function makes possible the calculation of contact angles that correspond to different MCs.

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Section: Methodsmentioning

confidence: 99%

Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

2021

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“…The contact angles, θ A and θ B , are determined by surface tensions, as the black arrows shown in Figure 3a, on three interfaces, which are the interfaces between any two of liquid, gas, and solid phases. The balance of the surface tensions on the three interfaces can be formulated by Young's law as [48] (γ…”

Section: Drag Force For Droplet Manipulationmentioning

confidence: 99%

Universal Plasma Jet for Droplet Manipulation on a PDMS Surface towards Wall-Less Scaffolds

Peng

Tsai

2021

Polymers

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Droplet manipulation is important in the fields of engineering, biology, chemistry, and medicine. Many techniques, such as electrowetting and magnetic actuation, have been developed for droplet manipulation. However, the fabrication of the manipulation platform often takes a long time and requires well-trained skills. Here we proposed a novel method that can directly generate and manipulate droplets on a polymeric surface using a universal plasma jet. One of its greatest advantages is that the jet can tremendously reduce the time for the platform fabrication while it can still perform stable droplet manipulation with controllable droplet size and motion. There are two steps for the proposed method. First, the universal plasma jet is set in plasma mode for modifying the manipulation path for droplets. Second, the jet is switched to air-jet mode for droplet generation and manipulation. The jetted air separates and pushes droplets along the plasma-treated path for droplet generation and manipulation. According to the experimental results, the size of the droplet can be controlled by the treatment time in the first step, i.e., a shorter treatment time of plasma results in a smaller size of the droplet, and vice versa. The largest and the smallest sizes of the generated droplets in the results are about 6 L and 0.1 L, respectively. Infrared spectra of absorption on the PDMS surfaces with and without the plasma treatment are investigated by Fourier-transform infrared spectroscopy. Tests of generating and mixing two droplets on a PDMS surface are successfully achieved. The aging effect of plasma treatment for the proposed method is also discussed. The proposed method provides a simple, fast, and low-cost way to generate and manipulate droplets on a polymeric surface. The method is expected to be applied to droplet-based cell culture by manipulating droplets encapsulating living cells and towards wall-less scaffolds on a polymeric surface.

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“…For such purposes, in relation to desired product, different gases are used: nitrogen/air (wet and dry), argon, and ozone plasma exposure [30,[50][51][52][53]. These various interactions of plasma with surfaces lead to different plasma-based surface modification strategies [54,55]. While the plasma exposure mainly induces increased surface roughness by etching on the scale of micrometre dimensions, chemical reactions caused by plasma exposure are known also to produce even finer scale changes in surface roughness [56,57].…”

Section: Introductionmentioning

confidence: 99%

“…It has been documented that the combination of micro and macro roughness gives the best results to control wettability as they act either to decrease the depth of air pockets, whilst simultaneously lowering the contact angle to enhance super-wettability, or, on the contrary, create surface patterning, which leads to liquid meniscus discontinuity and hence super-hydrophobicity [58][59][60]. Cold DBD plasma exposure of MNFC-based composites can, therefore, be an alternative to conventional treatments that utilise fossil-based chemicals that increase roughness and compatibility with other molecules and particles, such as dyes, conductive fillers and inks [55]. Larger contact area, when coupled with chemical moieties from different gas types can lead to the enhanced application of ultrafine coatings [37].…”

Section: Introductionmentioning

confidence: 99%

Iso- and Anisotropic Etching of Micro Nanofibrillated Cellulose Films by Sequential Oxygen and Nitrogen Gas Plasma Exposure for Tunable Wettability on Crystalline and Amorphous Regions

et al. 2021

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The surface of cellulose films, obtained from micro nanofibrillated cellulose produced with different enzymatic pretreatment digestion times of refined pulp, was exposed to gas plasma, resulting in a range of surface chemical and morphological changes affecting the mechanical and surface interactional properties. The action of separate and dual exposure to oxygen and nitrogen cold dielectric barrier discharge plasma was studied with respect to the generation of roughness (confocal laser and atomic force microscopy), nanostructural and chemical changes on the cellulose film surface, and their combined effect on wettability. Elemental analysis showed that with longer enzymatic pretreatment time the wetting response was sensitive to the chemical and morphological changes induced by both plasma gases, but distinctly oxygen plasma was seen to induce much greater morphological change while nitrogen plasma contributed more to chemical modification of the film surface. In this novel study, it is shown that exposure to oxygen plasma, subsequently followed by exposure to nitrogen plasma, leads first to an increase in wetting, and second to more hydrophobic behaviour, thus improving, for example, suitability for printing using polar functional inks or providing film barrier properties, respectively.

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The physics of water droplets on surfaces: exploring the effects of roughness and surface chemistry

Cited by 36 publications

References 38 publications

Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

Influence of moisture content on the contact angle and surface tension measured on birch wood surfaces

Universal Plasma Jet for Droplet Manipulation on a PDMS Surface towards Wall-Less Scaffolds

Iso- and Anisotropic Etching of Micro Nanofibrillated Cellulose Films by Sequential Oxygen and Nitrogen Gas Plasma Exposure for Tunable Wettability on Crystalline and Amorphous Regions

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