Patricia B. Weisensee

Bio: Patricia B. Weisensee is an academic researcher from Washington University in St. Louis. The author has contributed to research in topics: Condensation & Heat transfer. The author has an hindex of 11, co-authored 32 publications receiving 458 citations. Previous affiliations of Patricia B. Weisensee include University of Illinois at Urbana–Champaign & Technische Universität München.

Water droplet impact on elastic superhydrophobic surfaces.

Abstract: Water droplet impact on surfaces is a ubiquitous phenomenon in nature and industry, where the time of contact between droplet and surface influences the transfer of mass, momentum and energy. To manipulate and reduce the contact time of impacting droplets, previous publications report tailoring of surface microstructures that influence the droplet - surface interface. Here we show that surface elasticity also affects droplet impact, where a droplet impacting an elastic superhydrophobic surface can lead to a two-fold reduction in contact time compared to equivalent rigid surfaces. Using high speed imaging, we investigated the impact dynamics on elastic nanostructured superhydrophobic substrates having membrane and cantilever designs with stiffness 0.5-7630 N/m. Upon impact, the droplet excites the substrate to oscillate, while during liquid retraction, the substrate imparts vertical momentum back to the droplet with a springboard effect, causing early droplet lift-off with reduced contact time. Through detailed experimental and theoretical analysis, we show that this novel springboarding phenomenon is achieved for a specific range of Weber numbers (We >40) and droplet Froude numbers during spreading (Fr >1). The observation of the substrate elasticity-mediated droplet springboard effect provides new insight into droplet impact physics.

Hydrophobic and oleophobic re-entrant steel microstructures fabricated using micro electrical discharge machining

Abstract: This paper presents the fabrication of metallic micro-mushroom re-entrant structures and the characterization of their hydrophobicity and oleophobicity. Five different microstructure geometries are introduced, with typical feature sizes in the range of 10–100 μm. These microstructures are realized in steel, and are fabricated over the cm-scale using micro electrical discharge machining (mEDM). The liquid repellency of these surfaces is characterized using droplets of either water (surface energy γlg = 72.4 mN m−1), RL-68H oil (γlg = 28.6 mN m−1), or Isopropanol (IPA) (γlg = 21.7 mN m−1). The water droplets form nearly perfect spheres, with contact angles in the range 146–162°, and contact angle hysteresis of 19–35°. The oil droplet contact angles are in the range 106–152° and the IPA contact angles are in the range 75–123°. Strong re-entrant features and close spacing are necessary to support a fully non-wetting state for use with oil and IPA. Water forms the highest contact angles with narrow, post-like, and widely spaced micro-mushroom geometries.

Droplet impact on vibrating superhydrophobic surfaces

Abstract: A study using optical high speed imaging shows that droplet dynamics and contact times of water droplets impacting vibrating superhydrophobic surfaces depend on the vibration frequency, phase at impact, and amplitude of vibration. Contact times can be greater or smaller than the theoretical contact time on a nonvibrating surface.

Condensation heat transfer on superhydrophobic surfaces

Abstract: United States. Dept. of Energy. Office of Basic Energy Sciences (Solid-State Solar-Thermal Energy Conversion Center)

Liquid-Infused Surfaces: A Review of Theory, Design, and Applications.

Abstract: Due to inspiration from the Nepenthes pitcher plant, a frontier of devices has emerged with unmatched capabilities. Liquid-infused surfaces (LISs), particularly known for their liquid-repelling behavior under low tilting angles (<5°), have demonstrated a plethora of applications in medical, marine, energy, industrial, and environmental materials. This review presents recent developments of LIS technology and its prospective to define the future direction of this technology in solving tomorrow's real-life challenges. First, an introduction to the different models explaining the physical phenomena of these surfaces, their wettability, and viscous-dependent frictional forces is discussed. Then, an outline of different emerging strategies required to fabricate a stable liquid-infused interface is presented, including different substrates, lubricants, surface chemistries, and design parameters which can be tuned depending on the application. Furthermore, applications of LIS coatings in the areas of anticorrosion, antifouling, anti-icing, self-healing, droplet manipulation, and biomedical devices will be presented followed by the limitations and future direction of this technology.

Maximal deformation of an impacting drop

Abstract: are the liquid density and surface tension).This law is also observed to hold on partially wettable surfaces, provided that liquidsof low viscosity (such as water) are used. The law is interpreted as resulting fromthe effective acceleration experienced by the drop during its impact. Viscous dropsare also analysed, allowing us to propose a criterion for predicting if the spreading islimited by capillarity, or by viscosity.