Uniform Spread of High‐Speed Drops on Superhydrophobic Surface by Live‐Oligomeric Surfactant Jamming

Abstract

self-cleaning and antifouling ability for repelling the deposition of other materials and liquid confining properties for enhancing printing resolution and avoiding coffee-ring effects. [13] However, inertial water drops impacting superhydrophobic surfaces can bounce off quickly or splash violently. [14][15][16][17][18][19][20][21][22][23] Undesired rebound and splash cause material waste [24] and weaken the related performance and efficiency. Many attempts have been conducted to promote water drop spreading on hydrophobic surfaces by using polymers [1,23,[25][26][27][28] or surfactants. [22,[29][30][31][32] However, these two methods still have drawbacks for achieving drop deposition, not to mention uniform spreading: 1) Polymer additives can delay drop retraction but leave drops with hemispherical shape and nonuniform material distribution on the hydrophobic substrate.2) The poor wettability and large mole cular weight of polymer additives restrict the ejecting process during inkjet printing. 3) Surfactant additives can promote drop spreading in a static state owing to the reduced surface tension (γ); [33] however, the low surface tension increases the instability of the impacting drop and leads to drop splashing with satellite droplets, according to the Kelvin-Helmholtz instability, [34] k max ∼ 2ρ a U r 2 /3γ (ρ a is the air density). It is therefore a great challenge for uniform shape spreading on superhydrophobic surfaces without any loss of the drops. Here, we show a new and simple strategy for uniform round-shape drop spreading on superhydrophobic surfaces after high-speed impact, up to 5.0 m s −1 , by utilizing live-oligomeric surfactant jamming, diethylenetriamine/sodium dodecyl sulfate (triamine/SDS). The live-oligomeric surfactant, which noncovalently constructed by SDS and triamine through electrostatic interaction, has a dynamic equilibrium between monomer surfactant and oligomeric surfactant. Figure 1 shows the contrast spread dynamics of a liveoligomeric surfactant drop and other drops impacting superhydrophobic surfaces at an impacting velocity (U ) of 2.42 m s −1 from side and bottom views (Movie S1, Supporting Information). The diameter (D 0 ) of pure water and the surfactant drops is ≈2.25 and 1.90-2.00 mm, respectively (Figure S1, Supporting Information for experimental setup). The Weber number (We), We = ρDV 2 /γ, of water, SDS, N2C3/SDS, triamine/SDS, and 12-3-12-3-12 is 182. 68, 295.29, 358.29, 383.00, and 292.29, respectively. The superhydrophobic surface [35] composed of random micro-nanostructures of typical size and spacing of Inkjet printing of water-based inks on superhydrophobic surfaces is important in high-resolution bioarray detection, chemical analysis, and highperformance electronic circuits and devices. Obtaining uniform spreading of a drop on a superhydrophobic surface is still a challenge. Uniform round drop spreading and high-resolution inkjet printing patterns are demonstrated on superhydrophobic surfaces without splash or rebound after high-speed impacting by introducing...

Control the Entire Journey of Pesticide Application on Superhydrophobic Plant Surface by Dynamic Covalent Trimeric Surfactant Coacervation

“…[ 16,43–45 ] Several new approaches have been developed to improve the deposition efficiency by forming precipitate defecting, [ 18 ] transforming surface wettability, [ 19 ] and jamming the surface micro/nano structures. [ 20 ] However, the deposition and long‐term performance is still a challenge for the real water‐based pesticide formula. Figure shows the high‐speed drop deposition of the TIS10/pesticide coacervate (Figure 2a) on superhydrophobic cabbage leaves (Figure 2b–d, Movie S1, Supporting Information).…”

“…Thereby, the surface tension effect of TIS10 does not play an important role, that is, the mechanism for the present trimeric surfactant in inhibiting the splashing and retracting of droplets is different from that for other surfactants. [ 19,20,46 ]…”

“…A dip‐coating method via a literature procedure [ 20 ] was employed to fabricate a superhydrophobic surface on a glass substrate. The contact angle of water was tested about 160.4 ± 2.3°.…”

“…The characteristic time scale of water droplets is low to several milliseconds on superhydrophobic surface. To enhance pesticide utilization efficiency, mainstream researches have therefore established sub‐micrometer‐scaled assemblies and capsules to maximize the specific area for inhibiting rebound, [ 18–20 ] enhancing retention, [ 21,22 ] and controlling pesticide release. [ 5,23 ] Unfortunately, the assemblies applied to inhibiting the rebound have not considered the encapsulation ability and control release.…”

Bioinspired Surface with Superwettability for Controllable Liquid Dynamics

“…[ 35 ] In addition, pure liquids and mixed liquids with additives [ 36 ] are commonly used to study impact dynamics, such as the use of surfactants ( Figure a). [ 37,38 ] The composition of the droplet, the surface structures, or the chemical compositions of the solid surface can influence the impact process (Figure 3b). [ 39 ] Different impact outcomes, such as rebound, breakup, splash, and deposition, occur after the droplets impact the solid.…”