Dynamic Wettability on the Lubricant-Impregnated Surface: From Nucleation to Growth and Coalescence

Guo, Lin; Tang, G.H.; Kumar, Satish

doi:10.1021/acsami.0c03018

Cited by 34 publications

(24 citation statements)

References 45 publications

(75 reference statements)

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“…Water nucleation has been assumed to preferentially initiate at the oil−vapor interface of LISs due to limited vapor diffusion through the oil film as well as the low nucleation energy barrier at the oil−vapor interface. 15,18,38 A recent study showed that satellite droplets can also form on lubricant-cloaked water droplets during condensation on lubricant-infused micro-or nanotextured superhydrophobic surfaces. 39 Here, we focus on the influence of the microscopically uneven oil film on the inplane spatial preference for nucleation and note that we observe nucleation on the top of droplets only for the highest vapor temperatures.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces

2021

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Lubricant-infused surfaces (LISs) can promote stable dropwise condensation and improve heat transfer rates due to a low nucleation free-energy barrier and high droplet mobility. Recent studies showed that oil menisci surrounding condensate microdroplets form distinct oil-rich and oil-poor regions. These topographical differences in the oil surface cause water microdroplets to rigorously self-propel long distances, continuously redistributing the oil film and potentially refreshing the surface for re-nucleation. However, the dynamic interplay between oil film redistribution, microdroplet self-propulsion, and droplet nucleation and growth is not yet understood. Using high-speed microscopy, we reveal that during water condensation on LISs, the smallest visible droplets (diameter: ∼1 μm, qualitatively representing nucleation) predominantly emerge in oil-poor regions due to a lower nucleation free-energy barrier. Considering the significant heat transfer performance of microdroplets (<10 μm) and transient characteristic of microdroplet movement, we compare the apparent nucleation rate density and water collection rate for LISs with oils of different viscosities and a solid hydrophobic surface at a wide range of subcooling temperatures. Generally, the lowest lubricant viscosity leads to the highest nucleation rate density. We characterize the length and frequency of microdroplet movement and attribute the nucleation enhancement primarily to higher droplet mobility and surface refreshing frequency. Interestingly and unexpectedly, hydrophobic surfaces outperform high-viscosity LISs at high subcooling temperatures but are generally inferior to any of the tested LISs at low temperature differences. To explain the observed nonlinearity between LISs and the solid hydrophobic surface, we introduce two dominant regimes that influence the condensation efficiency: mobility-limited and coalescence-limited. We compare these regimes based on droplet growth rates and water collection rates on the different surfaces. Our findings advance the understanding of dynamic water–lubricant interactions and provide new design rationales for choosing surfaces for enhanced dropwise condensation and water collection efficiencies.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces

2021

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“…The detailed quantifications proposed in this study, for example, the equilibrium radius of the drop (which signifies the extent of wetting of the “surface” by the “liquid” in our hypothesized LIS), the time-dependent spreading and wicking behaviors (which signify how fast the fabrication of the LIS occurs), and the time-dependent response of the polymer molecules (which signify the “responsiveness” of the “responsive” surface), enable a nanoscopic quantification of designing an LIS or a coating. Earlier MD simulation studies have probed the dynamics of a liquid drop interacting with a pre-existing LIS; , however, these studies have not considered the nanoscale dynamics associated with the formation of a soft and responsive LIS, as has been considered here. Additionally, there are several other facets of this hypothesized LIS or coating that are worth (re)emphasizing.…”

Section: Resultsmentioning

confidence: 99%

“…Studying the behavior of liquid drops on the surfaces of various complexities has been critical in designing and fabricating a wide variety of surfaces that demonstrate different wettabilities − which could be employed in various energy − and biomedical , applications as well as applications such as heat-transfer enhancement, − fabrication of anti-biofouling, − anti-corrosion, − anti-icing, − anti-bacterial, and anti-thrombotic surfaces, enhanced oil–water separation, , and many more. Advancement of computational techniques have enabled a nanoscale exploration of the drop–substrate interactions shedding light on fundamental mechanisms dictating these different interactions as well as enabling designing of surfaces with novel properties. − …”

Section: Introductionmentioning

confidence: 99%

Wetting Dynamics on Solvophilic, Soft, Porous, and Responsive Surfaces

et al. 2021

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We employ molecular dynamics (MD) simulations to study the spreading and imbibition of a liquid drop on a porous, soft, solvophilic, and responsive surface represented by a layer of polymer molecules grafted on a solvophilic solid. These polymer molecules are in a crumpled and collapsed globule-like state before the interaction with the drop but transition to a “brush”-like state as they get wetted by the liquid drop. We hypothesize that for a wide range of densities of polymer grafting (σg), the drop spreading is dictated by the balance of the driving inertial pressure and balancing viscoelastic dissipation (associated with the spreading of the liquid drop on the polymer layer that undergoes globule-to-brush transition and serves as the viscoelastic solid). Using the well-known idea that the viscoelastic resisting force exerted by the viscoelastic solid on a spreading drop scales as u n (where n is the index of the power-law-like rheology of the polymer layer serving as the viscoelastic solid and u is the spreading velocity of the drop on this viscoelastic solid) and considering n = 2/3, we show that the scaling calculation recovers the MD simulation prediction of r ∼ t 1/4 and r eq ∼ σg –1/3 (where r and r eq are the instantaneous and equilibrium spreading radii, respectively). We further describe the wicking behavior of the drop through the polymer layer by appropriately accounting for the manner in which the progressive time-dependent swelling of the grafted polymer molecules provides larger space for the wicking. Third, we quantify, possibly for the first time, the temporal dynamics of the “brush”-forming process (i.e., capture the dynamics of wetting-mediated globule-to-brush transition). We show that the dynamics of the polymer chain swelling depends on σg and is faster for sparser grafting. Most importantly, we confirm that the height of the relaxed polymer chains approximately scales as σg 1/3, confirming the attainment of brush-like configuration by the polymer molecules as they are wetted by the liquid drop. Finally, we argue that our simulations raise the possibility of designing soft, “responsive”, and widely deployable liquid-infused surfaces where the polymer grafted solid, with the polymer undergoing a globule-to-brush transition, serves as the responsive “surface”.

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“…In the follow-up study, 36 the coalescence-induced condensation droplet jumping was explored in detail, and it was found that the diameter and maximum jumping height would reduce with the increase of NCG fraction. Molecular dynamics simulation has been widely used to investigate droplet nucleation and growth for pure vapor 37,38 but few studies focus on the mixture condensation. The evaporation and condensation of fluid Ar in the presence of a noncondensable Ne gas was investigated 39 and the molar fluxes predicted by Schrage relationships are in good agreement with the simulation results.…”

Section: Introductionmentioning

confidence: 99%

Droplet Nucleation and Growth in the Presence of Noncondensable Gas: A Molecular Dynamics Study

2021

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The presence of noncondensable gas (NCG) followed by undesirable heat transfer deterioration cannot be avoided in some situations. In this work, droplet nucleation and growth for the Ar−Ne mixed system are investigated using molecular dynamics simulation. Different droplet state transition modes corresponding to the subcooling degree or NCG content are obtained. The interaction between NCG and a droplet caused by gas enrichment near the solid surface is considered to explain the droplet wetting state during the condensation process. Finally, the disappearance mechanism of the flooding mode on the nanostructured surface under a large amount of NCG is clarified from the nanoscale, which could encourage a clear understanding of the NCG effect on dropwise condensation heat transfer on nanostructured superhydrophobic surfaces.

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Dynamic Wettability on the Lubricant-Impregnated Surface: From Nucleation to Growth and Coalescence

Cited by 34 publications

References 45 publications

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces

Wetting Dynamics on Solvophilic, Soft, Porous, and Responsive Surfaces

Droplet Nucleation and Growth in the Presence of Noncondensable Gas: A Molecular Dynamics Study

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