$102,590 grant to accelerate student learning, encourage innovation among faculty and students, and support fast-growing economic sectors through technology development and entrepreneurship. Learn More
Dr. Liv Hasselbach and Dr. Jerry Lin
Liv Hasselbach received a $100,000 grant from the Sabine River Authority of Texas (SRA) with Jerry Lin (CAWAQ) to work on flood strategies. Initiate the Southeast Texas Flood Coordination Study, a collaborative project designed to help the region improve its resiliency during large-scale flooding. Learn More
Dr. Henry Venta and Dr. James Slaydon
$440,000 grant to develop a framework for EDA to implement to help Southeast Texas recover from disasters such as Tropical Storm Harvey. Learn More
Chun-Wei Yao, Sirui Tang, Divine Sebastian, and Rafael Tadmor, February 28, 2020
Abstract: Understanding the specific behavior of water droplet detachment from a micropillar-structured superhydrophobic surface is essential in a variety of potential applications. Herein, the sliding behavior of water droplets on three different micropillar-structured superhydrophobic surfaces was studied. From tilting plate experiments and retention force measurements, we probed the motion of water droplets with different volumes. The effects of droplet sizes and contact angle hysteresis on the roll-off angle were also investigated. Furthermore, three different models are proposed to estimate a roll-off angle. The lateral retention force-based model agrees well with the roll-off angle measurements, and the other two contact angle hysteresis-based models capture the trend in the variation of the roll-off angle. Read More at Science Direct
Chae Rohrs, Arash Azimi, and Ping He, October 30, 2019
Abstract: A liquid droplet on a micropatterned substrate equalizes into either the Cassie−Baxter (also called Cassie for short) or the Wenzel state. This paper investigates the wetting phenomena on ideal micropatterned surfaces consisting of straight micropillars at different pillar dimensions and spacings (the word “ideal” refers to being chemically homogeneous and free of submicron-scale roughness all over the micropatterned surface). Two modeling approaches are used: (1) a thermodynamic approach analyzing the Gibbs energy of the droplet−solid−gas system and (2) a computational fluid dynamics (CFD) approach studying the three-dimensional dynamic wetting process to validate the results of the first approach. The thermodynamic approach incorporates three creative submodels proposed in this paper: (i) a sagging model explaining the pillar edge effect, (ii) a touchdown model transitioning the droplet’s partial penetrating condition toward its full penetrating condition, i.e., the Wenzel state, and (iii) a liquid-volume model dynamically computing the liquid volume between the pillar valleys while in the partial penetrating condition or in the Wenzel state. The results of the thermodynamic approach reveal (1) a small energy barrier between the Cassie and Wenzel states, (2) no partial penetration and sagging of the liquid in the Cassie state on the ideal straight micropillared surface, and (3) that the apparent contact angle in the most stable Wenzel state can be 5° or more lower than the prediction of the Wenzel equation when the pillar height is equal or greater than 75 μm. To the best of our knowledge, this paper presents the theoretical explanation of this Wenzel deviation on micropatterned surfaces for the first time in the literature. Utilizing the state-of-the-art continuum model developed by the authors in previous studies, the CFD approach investigates the same wetting conditions and confirms the same findings. Learn More
Ping He and Chun-Wei Yao, June 27, 2019
Abstract: Pseudo-line tensions are used in a continuum approach to simulate contact angle hysteresis. A pair of pseudo-line tensions in the receding and advancing states, respectively, are utilized to represent contact line interactions with a substrate because of the nanoscale topological and/or chemical heterogeneity on the substrate. A water droplet sitting on a horizontal or inclined substrate, whose volume is 4–30µL, has been studied experimentally and numerically. Our simulation model predicts consistent hysteresis at four different droplet sizes compared with experiments. Meanwhile, the critical roll-off angles captured in simulations match well with experiments. Learn More
Fransisco A. Sanchez, Ping He, Ahmed F. Ghoniem, and Selva Pereda, December 21, 2018
Abstract: In this work, the mixing of a hydrocarbon droplet in near- and super-critical water (NCW/SCW) is mathematically modeled, coupling thermodynamic properties calculation with transport processes. In non-ideal systems, mass transfer is captured using the generalized Maxwell-Stefan equations with the driving force expressed in terms of the fugacity gradients. The GCA-EOS is used to predict the thermodynamic properties and phase equilibrium compositions. We select n-decane, n-triacontane, benzene, naphthalene and 1-decylnaphthalene as representative hydrocarbons. Our simulations show delayed mixing processes as the temperature approaches the upper critical solution temperature (UCST) of the mixture, consistent with the impact of non-ideal diffusional driving forces evaluated from pure thermodynamic calculations. Results also show that the phase behavior notably affects the non-ideal driving forces near the UCST, which confirms the importance of coupling accurate thermodynamic models in predictive mixing studies. Learn More
Chae Rohrs, Arash Azimi, Chun-WeiYao, and Ping He, August 22, 2018
Abstract: Modeling static and dynamic contact angles is a great challenge in studying wetting and de-wetting. We propose a new slip boundary model based on the Navier–Stokes equations, and establish a realistic continuum approach to simulate the contact line dynamics in 3-D. To validate our model, a water droplet interacting with micrometer-sized patterns of a hybrid hydro-phobic/-philic surface is studied numerically and compared with experimental measurements. Good agreement has been observed with four pillar spacings in the static, receding, and advancing modes. Moreover, details of the droplet–surface interaction are revealed, i.e., penetrations, sagging, local, and global contact angles. Learn More