Dynamic hydrophobicity on flat and pillared graphite surfaces with different pillar surface fractions

Matthew Stanley Ambrosia,하만영,S. Balachandar 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.2

The motion of a droplet on a surface is of importance to many fields. While many things are known at the macro-scale still a completeunderstanding of fluid flow at the nano-scale is far from being known. This study focuses on the dynamic hydrophobicity of a pillar surfacewith different pillar surface fractions at the nano-scale using molecular dynamics simulations. Five pillar heights and four pillar surfacefractions were modeled using a graphite surface which has anisotropic characteristics due to its spaced layers. A nano-sized waterdroplet with 5124 molecules was run to equilibrium on each surface. Then a body force was applied and the dynamic contact angles werecalculated for 5 ns. These contact angles were used to calculate the surface’s effective hydrophobicity. The droplets were categorized intoone of three groups as different phenomena were identified depending on the pillar surface fraction, applied force, and pillar height. Itwas found that at the nano-scale smooth, flat surfaces are dynamically more hydrophobic than any of the cases with pillars. Larger pillarsurface fractions tended to be more hydrophobic and the pillar surface fraction of 36% was least affected by pillar height and appliedbody force.

Original Article : A Study of a Hydrophobic Surface: Comparing Pure Water and Contaminated Water

( Matthew Stanley Ambrosia ),( Chang Han Lee ) 한국환경과학회 2013 한국환경과학회지 Vol.22 No.4

The flow of sewage has been studied for hundreds of years. Reducing drag in pipes can allow sewer to be removed easily and quickly. Drag reduction is not only a macroscale issue. Physical and chemical properties of the nano-scale can affect flow at the macroscopic scale. In this paper the predictability of hydrophobicity at the nano-scale is studied. Molecular dynamics simulations were used to calculate the range of contact angles of water droplets in equilibrium on a pillared graphite surface. It was found that at a pillar height of two graphite layers there was the largest range of contact angles. It is observed that at this height the droplet begins to transition from the Wenzel state to the Cassie-Baxter state. Surfaces with larger pillar heights have much larger contact angles corresponding to a more hydrophobic surface. Silicon dioxide was also simulated in the water droplet. The contaminant slight decreased the contact angle of the water droplet.

A molecular dynamics study of Wenzel state water droplets on anisotropic surfaces

Ambrosia, Matthew Stanley,Ha, Man Yeong Elsevier 2018 Computers & fluids Vol.163 No.-

<P><B>Abstract</B></P> <P>Some phenomena at the nanoscale are different from those at the macroscale. One of these phenomena is represented by the Wenzel equation which predicts a droplet's contact angle on a textured surface under certain conditions at the macroscale. However, at the nanoscale a different trend is observed in some cases. The Wenzel equation predicts contact angles to decrease as the surface roughness factor increases for droplets with a Young contact angle under 90°. However, for these cases at the nanoscale contact angles become larger as the surface roughness factor increases. In this study molecular dynamic simulations were run to investigate this phenomenon. Five surface energies and five surface roughness factors were considered for a graphite-like surface. Contact angles of nanoscale water droplets on an anisotropic surface with nanoscale texture are plotted and an equation related to the surface roughness factor and Young contact angle that fits the trend is proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Water droplets in the Wenzel state have larger contact angles at the nanoscale than the Wenzel equation predicts. </LI> <LI> At the nanoscale water droplets have a larger contact angles when the graphite layers are oriented vertically than horizontally. </LI> <LI> Water droplets at the nanoscale generally increase as the surface roughness factor increases regardless of the Young contact angle. </LI> <LI> A logarithmic equation dependent on the surface roughness factor models contact angles on pillared graphite at the nanoscale. </LI> </UL> </P>

PC24) Observing Oxygen Molecules Interacting with a Water Surface at Different Temperatures

Matthew Stanley Ambrosia 한국환경과학회 2018 한국환경과학회 학술발표회 발표논문집 Vol.2018 No.11

A Molecular Dynamics Study of the Interaction of Oxygen Molecules with a Water Droplet

( Matthew Stanley Ambrosia ) 한국환경과학회 2018 한국환경과학회지 Vol.27 No.10

Water and oxygen are two of the most essential molecules for many species on earth. Their unique properties have been studied in many areas of science. In this study, the interaction of water and oxygen molecules was observed at the nano-scale. Using molecular dynamics, a water droplet with 30,968 water molecules was simulated. Then, 501 oxygen molecules were introduced into the domain. A few oxygen molecules were attracted to the surface of the water droplet due to van der Waals forces, and some oxygen molecules actually entered the water droplet. These interactions were visualized and quantified at four temperatures ranging from 280 to 370 K. It was found that at high temperatures, there was a higher possibility of the oxygen molecules penetrating the water droplet than that at lower temperatures. However, at lower temperatures, oxygen molecules were more likely to be found interacting at the surface of the water droplet than at high temperatures.

미세기포 발생 펌프 내 체류시간에 따른 미세기포의 발생 농도 예측

매튜스탠리암브로샤 ( Matthew Stanley Ambrosia ),이창한 ( Chang Han Lee ) 한국환경과학회 2016 한국환경과학회지 Vol.25 No.6

The mechanism of micro-bubble generation with a pump is not clarified yet, so the design of water treatment systems with a micro-bubble generating pump is based on trial and error methods. This study tried to explain clearly quantitative relationships of experimental micro-bubble concentration (Cair) of continuous operation tests with a micro-bubble generating pump and theoretical air solubility. Operation parameters for the tests were discharge pressure (Pg), water (Qw0) and air (q0) flow rates, orifice diameter (DO), and retention time (t). The experimental micro-bubble concentrations (Cair) at 4.8 atm of discharge pressure (Pg) were in the range of 21.04 to 25.29 mL/L. When the retention time (t) by changing the pipe line length (LP) increased from 1.22 to 6.77s, the experimental micro-bubble concentrations (Cair) increased from 25.86 to 30.78 mL air/L water linearly. The dissolved and dispersed micro-bubble concentrations (Cair) are approximately 4 times more than the theoretical air solubility.

ORIGINAL ARTICLE : Kinetics and Thermodynamic Properties Related to the Adsorption of Copper and Zinc onto Zeolite Synthesized from Coal Fly Ash

( Chang Han Lee ),( Matthew Stanley Ambrosia ) 한국환경과학회 2013 한국환경과학회지 Vol.22 No.10

Na-A zeolite (Z-Cl) was synthesized from coal fly ash, which is a byproduct of coal combustion for the generation of electricity. The adsorption of Cu2+ and Zn2+ions onto Z-C1 was investigated via batch tests over a range of temperatures (303.15 to 323.15 K). The resultant experimental equilibrium data were compared to theoretical values calculated using model equations. With these results, the kinetics and equilibrium parameters of adsorption were calculated using Lagergren and Langmuir-Freundlich models. The adsorption kinetics revealed that the pseudo second-order kinetic mechanism is predominant. The maximum adsorption capacity (qmax) values were 139.0-197.9 mg Zn2+/g and 75.0-105.1 mg Cu2+/g. Calculation of the thermodynamic properties revealed that the absorption reactions for both Cu2+and Zn2+ were spontaneous and endothermic. Collectively, these results suggest that the synthesized zeolite, Z-C1, can potentially be used as an adsorbent for metal ion recovery during the treatment of industrial wastewater at high temperatures.

Release of Oxygen from a Nano-sized Water Droplet Observed using Molecular Dynamics

( Chang-han Lee ),( Matthew Stanley Ambrosia ) 한국환경과학회 2016 한국환경과학회지 Vol.25 No.7

Dissolved oxygen is necessary for many biological processes as well as many industrial practices. Dissolved oxygen released from water in dissolved air flotation (DAF) systems can be have many different applications. However, DAF systems are very costly to operate. To develop more efficient DAF systems, a deeper understanding of the process of oxygen being released from water is required. In this study, molecular dynamics (MD) simulations were used to simulate 100 oxygen molecules surrounded by 31002 water molecules at temperatures ranging from 0℃ to 100℃. Simulations were carried out for 10 ns, during which, in most cases, all the oxygen molecules were released from the water droplet. With MD simulations, visualization of the molecules escaping the water droplet was possible, which aided the understanding of the interactions between molecules at the nano-scale. The results showed that as the oxygen molecules moved near the edge of the water droplet that the oxygen molecules hesitated before escaping the water droplet or returned to the interior of the water droplet. This was because of the attractive forces between the water and oxygen molecules. Moreover, after most of the oxygen molecules were released from the droplet, some were found to return to the droplet``s edge or even the interior of the droplet. It was also confirmed that oxygen molecules were released at a faster rate at higher temperatures.

분자동역학을 이용한 계층 구조를 갖는 표면의 소수성에 대한 연구

권태우(Tae Woo Kwon),장준경(Joonkyung Jang),Matthew Stanley Ambrosia,하만영(Man Young Ha) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

Using all-atom molecular dynamics simulation, we investigated the wetting behavior of a water droplet on a surface texturized with nanoscale pillars. We studied the surfaces with nonhierarchical and hierarchical roughnesses by systematically varying the pillar height. A surface decorated with a hierarchical roughness showed an enhanced hydrophobicity in that the droplet on such a surface prefers the Cassie-Baxter state over the Wenzel state. A hierarchical roughness also gave an enhanced contact angle of a droplet. Even a hydrophilic surface (contact angle is < 90°) turned hydrophobic (contact angle > 90°) with a hierarchical roughness on it. We show the adhesion energy of a droplet to its underlying surface is correlated with the contact angle and therefore is a fundamental measure of the wettability of the

분자동역학을 이용한 사각 기둥과 이중구조 기둥 위에서의 수액적의 정적 특성에 대한 비교

이광호(Gwang Ho Lee),권태우(Tae Woo Kwon),하만영(Man Young Ha),Matthew Stanley Ambrosia 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

In the present study, a numerical study was conducted to investigate a statistic behaviors of the water droplet on plate that adheres various structure pillars by molecular dynamics simulation. There are two kinds of plate having rectangular-structure pillar and the dual structures pillar, which contain constant characteristic energy. We conducted the computational simulation that an initial water cube reached an equilibrium state as a water droplet. And then we observed the static behaviors of the water droplet depended on their shapes and the pillar characteristics (e.g., the structure and the height).