Tuning static drop friction

Laroche, Alexandre; Naga, Abhinav; Hinduja, Chirag; Sharifi, Azadeh Aghili; Saal, Alexander; Kim, Hyeonjin; Gao, Nan; Wooh, Sanghyuk; Butt, Hans‐Jürgen; Berger, Rüdiger; Vollmer, Doris

doi:10.1002/dro2.42

“…There are many methods to study drop dynamics, such as using de-/inflated drops 9 , magnetically controlled oscillated drops 10 , direct force measurements with force sensors 11 , 12 , and sliding drops on a tilted surface 13 . When drops slide down tilted surfaces, the external gravitational force driving the motion, , can be adjusted by the tilt angle , to control droplet velocity in a wide range.…”

Section: Introductionmentioning

confidence: 99%

Kinetic drop friction

Li

¹

,

Bodziony

²

,

Yin

³

et al. 2023

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Liquid drops sliding on tilted surfaces is an everyday phenomenon and is important for many industrial applications. Still, it is impossible to predict the drop’s sliding velocity. To make a step forward in quantitative understanding, we measured the velocity $$(U)$$ ( U ) , contact width $$(w)$$ ( w ) , contact length $$(L)$$ ( L ) , advancing $$({\theta }_{{{{{{\rm{a}}}}}}})$$ ( θ a ) , and receding contact angle $$({\theta }_{{{{{{\rm{r}}}}}}})$$ ( θ r ) of liquid drops sliding down inclined flat surfaces made of different materials. We find the friction force acting on sliding drops of polar and non-polar liquids with viscosities ($${\eta }$$ η ) ranging from 10−3 to 1 $${{{{{\rm{Pa}}}}}}\cdot {{{{{\rm{s}}}}}}$$ Pa ⋅ s can empirically be described by $${F}_{{{{{{\rm{f}}}}}}}(U)={F}_{0}+\beta w\eta U$$ F f ( U ) = F 0 + β w η U for a velocity range up to 0.7 ms−1. The dimensionless friction coefficient $$(\beta )$$ ( β ) defined here varies from 20 to 200. It is a material parameter, specific for a liquid/surface combination. While static wetting is fully described by $${\theta }_{{{{{{\rm{a}}}}}}}$$ θ a and $${\theta }_{{{{{{\rm{r}}}}}}}$$ θ r , for dynamic wetting the friction coefficient is additionally necessary.

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“…The design principles presented here provide a foundation for new types of surfaces relevant to superwater repellent applications, [ 39 ] liquid encapsulation, [ 33,40 ] and microreactors, [ 41,42 ] and may also have an application to strain controllable liquid–liquid separations [ 43 ] or droplet catch‐and‐release. [ 44 ]…”

Section: Discussionmentioning

confidence: 99%

Transforming Auxetic Metamaterials into Superhydrophobic Surfaces

McHale,

Alderson,

Armstrong

et al. 2024

Small Structures

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Superhydrophobic materials are often inspired by nature, whereas metamaterials are engineered to have properties not usually occurring naturally. In both, the key to their unique properties is structure. Here, it is shown that a negative Poisson's ratio (auxetic) mechanical metamaterial can transform into a unique superhydrophobic material. When stretched, its surface has the counterintuitive property that it also expands in the orthogonal lateral direction. The change in the solid surface fraction as strain is applied is modeled, and it is shown that it decreases as the space between solid elements of the auxetic lattice expands. This results in a unique dependence of the superhydrophobicity on strain. Experimental models are constructed to illustrate the relationship between different states of strain and superhydrophobicity as the lattice transitions from an auxetic to a conventional structure. The findings offer a new approach to designing superhydrophobic materials for self‐cleaning surfaces, droplet transportation, droplet encapsulation, and oil–water separation.

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“…4c) 90 . Recently, Laroche et al showed that static F fric can vary by as much as 30% depending on how the drop is deposited, whereas kinetic F fric is independent of drop history 91 .…”

Section: Wetting Force Measurementsmentioning

confidence: 99%

Probing surface wetting across multiple force, length and time scales

Daniel

¹

,

Vuckovac

²

,

Backholm

³

et al. 2023

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Surface wetting is a multiscale phenomenon where properties at the macroscale are determined by features at much smaller length scales, such as nanoscale surface topographies. Traditionally, the wetting of surfaces is quantified by the macroscopic contact angle that a liquid droplet makes, but this approach suffers from various limitations. In recent years, several techniques have been developed to address these shortcomings, ranging from direct measurements of pinning forces using cantilever-based force probes to atomic force microscopy methods. In this review, we will discuss how these new techniques allow for the probing of surface wetting properties in far greater detail. Advances in surface characterization techniques will improve our understanding of surface wetting and facilitate the design of functional surfaces and materials, including for antifogging and antifouling applications.

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Tuning static drop friction

Cited by 7 publications

References 41 publications

Kinetic drop friction

Kinetic drop friction

Transforming Auxetic Metamaterials into Superhydrophobic Surfaces

Probing surface wetting across multiple force, length and time scales

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