Voltage-induced spreading and superspreading of liquids

McHale, Glen; Brown, C. V.; Sampara, Naresh

doi:10.1038/ncomms2619

Cited by 98 publications

(93 citation statements)

References 29 publications

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“…For drops with R > λ c , the effect of gravity as a driving force for spreading becomes more relevant, and drop spreading follows another power law r ∼ R( Rρg μ ) 1/8 t 1/8 [10,23]. On partially wetting substrates, spreading drops approach equilibrium with an exponential law [15,24].…”

Section: Introductionmentioning

confidence: 96%

Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops

2014

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In this paper, we experimentally investigated the dynamic spreading of liquid drops on solid surfaces. Drop of glycerol water mixtures and pure water that have comparable surface tensions (62.3-72.8 mN/m) but different viscosities (1.0-60.1 cP) were used. The size of the drops was 0.5-1.2 mm. Solid surfaces with different lyophilic and lyophobic coatings (equilibrium contact angle θ(eq) of 0°-112°) were used to study the effect of surface wettability. We show that surface wettability and liquid viscosity influence wetting dynamics and affect either the coefficient or the exponent of the power law that describes the growth of the wetting radius. In the early inertial wetting regime, the coefficient of the wetting power law increases with surface wettability but decreases with liquid viscosity. In contrast, the exponent of the power law does only depend on surface wettability as also reported in literature. It was further found that surface wettability does not affect the duration of inertial wetting, whereas the viscosity of the liquid does. For low viscosity liquids, the duration of inertial wetting corresponds to the time of capillary wave propagation, which can be determined by Lamb's drop oscillation model for inviscid liquids. For relatively high viscosity liquids, the inertial wetting time increases with liquid viscosity, which may due to the viscous damping of the surface capillary waves. Furthermore, we observed a viscous wetting regime only on surfaces with an equilibrium contact angle θ(eq) smaller than a critical angle θ(c) depending on viscosity. A scaling analysis based on Navier-Stokes equations is presented at the end, and the predicted θ(c) matches with experimental observations without any additional fitting parameters.

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Section: Introductionmentioning

confidence: 96%

Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops

2014

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“…For drops with R>λ c , the effect of gravity as a driving force for spreading becomes more relevant, and drop spreading follows another power law, rR (Rρg/μ) 1/8 t 1/8 [10,14]. On partially wetting substrates, spreading drops approach equilibrium with an exponential law [2,15].…”

Section: Introductionmentioning

confidence: 99%

Comparison of spontaneous wetting and drop impact dynamics of aqueous surfactant solutions on hydrophobic polypropylene surfaces: scaling of the contact radius

2014

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In this paper, we comparatively investigated the spontaneous wetting and the impact dynamics of surfactantladen drops on hydrophobic polypropylene surfaces. We used the organic anionic surfactant sodium dodecyl sulfate (SDS) and two silicone-based nonionic surfactants, one of which was a so-called superspreader. The wetting dynamics during spontaneous spreading could be divided into an early inertiadominated stage and a later viscosity-dominated stage. Both could be described by power laws with different exponents. Further, wetting dynamics during the faster inertial stage was independent of surfactant properties, while surfactants played a role in the slower viscous stage. During drop impact, regardless of the impact speed the early wetting stage was controlled by inertial and capillary forces only. But, different from spontaneous spreading, surfactants influenced the wetting dynamics of this early stage. After the drops reached the maximum spreading radius r max they started recoiling and reducing again their contact radius. We observed, however, that despite reducing the static surface tension of the water drops, not all surfactants promoted them to spread out to a larger radius than the pure water drops during the early impact stage. We thus introduced a new time scale, τ ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi ρr 3 max =γ p , that uses the maximum spreading radius of the drops upon impact and that allows rescaling the durations of the inertial wetting stages to a universal master curve. Finally, we observed that only those drops containing superspreader restarted wetting the surface after recoiling, but the dynamics is not yet completely clear.

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“…Notably, the surfactant concentration for maximal spreading rates occurs just below a bulk-phase transition from surfactant vesicles to lamellar phases. [1][2][3][4][5][6][7][8] Superspreading is the only known mechanism, with the possible exception of voltageinduced spreading, 9 that can lead to rapid spreading. 10 It is therefore highly relevant to both fundamental physics, because of the violation of typically known spreading laws, and to industrial applications, because of the need to optimize the effect and to develop alternative superspreading agents, as current superspreading agents are known to be toxic.…”

Section: Introductionmentioning

confidence: 99%

Smoothing of contact lines in spreading droplets by trisiloxane surfactants and its relevance for superspreading

2015

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ab Superspreading, the greatly enhanced spreading of aqueous solutions of trisiloxane surfactants on hydrophobic substrates, is of great interest in fundamental physics and technical applications. Despite numerous studies in the last 20 years, the superspreading mechanism is still not well understood, largely because the molecular scale cannot be resolved appropriately either experimentally or using continuum simulations. The absence of molecular-scale knowledge has led to a series of conflicting hypotheses based on different assumptions of surfactant behavior. We report a series of large-scale molecular dynamics simulations of aqueous solutions of superspreading and non-superspreading surfactants on different substrates. We find that the transition from the liquid-vapor to the solid-liquid interface is smooth for superspreading conditions, allowing direct adsorption through the contact line. This finding complements a study [Karapetsas et al., J. Fluid Mech., 2011, 670, 5-37], which predicts that superspreading can occur if this adsorption path is possible. Based on the observed mechanism, we provide plausible explanations for the influence of the substrate hydrophobicity, the surfactant chain length, and the surfactant concentration on the superspreading phenomenon. We also briefly address that the observed droplet shape is a mechanism to overcome the Huh-Scriven paradox of infinite viscous dissipation at the contact line.

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Voltage-induced spreading and superspreading of liquids

Cited by 98 publications

References 29 publications

Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops

Effects of surface wettability and liquid viscosity on the dynamic wetting of individual drops

Comparison of spontaneous wetting and drop impact dynamics of aqueous surfactant solutions on hydrophobic polypropylene surfaces: scaling of the contact radius

Smoothing of contact lines in spreading droplets by trisiloxane surfactants and its relevance for superspreading

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