Functional liquid droplets for analyte sensing and energy harvesting

Thakur, Siddharth; Dasmahapatra, Ashok Kumar; Bandyopadhyay, Dipankar

doi:10.1016/j.cis.2021.102453

Cited by 8 publications

(4 citation statements)

References 142 publications

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“…The electrification of water droplets after sliding or rolling on hydrophobic surfaces has increasing interest for its applications in energy harvesting devices. − A particular case corresponds to the slide/roll of water drops on hydrophobic polymers, poly(tetrafluoroethylene) (PTFE) being the paradigmatic polymer for observing this phenomenon. The situation to describe is the following: water drops are delivered, one after another, on the tilted (almost vertical) surface of a hydrophobic polymer (see Figure ).…”

Section: Introductionmentioning

confidence: 99%

Liquid–Polymer Contact Electrification: Modeling the Dependence of Surface Charges and ξ-Potential on pH and Added-Salt Concentration

et al. 2022

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Here, a mathematical model is presented, which accounts for the dependence of the surface electrical charge density (σ) on pH and the concentration of added salts (C s), generated when a water drop rolls or slides on the surface of a hydrophobic polymer, a process known as liquid–polymer contact electrification (LPCE). The same model was successfully applied to fit the isotherms of ξ-potential as a function of pH, reported in the literature by other authors for water–poly(tetrafluoroethylene) (PTFE) interfaces. Hence, the dependence of σ and ξ on pH was described using the same concept: acid–base equilibria at the water–polymer interface. Equilibrium constants were estimated by fitting experimental isotherms. The experimental results and the model are consistent with a number of 10–100 acid–base sites/μm2. The model predicts the increase of |σ| and |ξ| with pH in the range of 2–10 and the existence of a zero-charge point at pHzcp ≅ 3 for PTFE (independent of C s). Excellent fits were obtained with K a/K b ∼ 9 × 107, where K a and K b are the respective acid and base equilibrium constants. On the other hand, the observed decrease in |σ| and |ξ| with C s at fixed pH is quantitatively described by introducing an activity factor associated with the quenching of water activity by the salt ions at the polymer–water interface, with quenching constant K q. Additionally, the quenching predicts a decrease in |σ| and |ξ| at extreme pH, where I > (1/K q) (I: ionic strength), in agreement with literature reports.

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Section: Introductionmentioning

confidence: 99%

Liquid–Polymer Contact Electrification: Modeling the Dependence of Surface Charges and ξ-Potential on pH and Added-Salt Concentration

et al. 2022

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“…[ 48 ] Moreover, we may further utilize the interfacial properties of the precursor solution such as Plateau–Rayleigh instability and beads‐on‐a‐string structures, which can further tune the fine structures of fibers, showing potentials in water collection, [ 49 ] directional transport, [ 50 ] and energy harvesting. [ 51 ]…”

Section: Discussionmentioning

confidence: 99%

Dry‐Spinning of Artificial Spider Silk Ribbons From Regenerated Natural Spidroin in an Organic Medium

Wang

Zhang

Chen

et al. 2023

Macromol. Rapid Commun.

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Natural spider silks with striking performances achieve extensive investigations. Nonetheless, a lack of consensus over the mechanism of the natural spinning hinders the development of artificial spinning methods where the regenerated spider silks generally show poor performances compared with the natural fibers. As is known, the Plateau–Rayleigh instability tends to break solution column into droplets and is considered a main challenge during fiber‐spinning. Here in this study, by harnessing the viscoelastic properties of the regenerated spidroin dope solution via organic salt–zinc acetate (ZA), this outcome can be avoided, and dry‐spinning of long and mechanically robust regenerated spider silk ribbons can be successfully realized. The as‐obtained dry‐spun spider silk ribbons show an enhanced modulus up to 14 ± 4 GPa and a toughness of ≈51 ± 9 MJ m−3 after the post‐stretching treatment, which is even better than that of the pristine spider silk fibers. This facile and flexible strategy enriches the spinning methodologies which bypass the bottleneck of precisely mimicking the complex natural environment of the glands in spiders, shining a light to the spider‐silk‐based textile industrial applications.

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“…13−17 Droplet dynamics and their interfacial flow underpins small-scale liquid systems such as coating, 18 water collection, 19,20 emulsification, 21 sensing, 22,23 and energy harvesting. 24,25 Marangoni flows, created by either thermal or solutal-effect-induced surface tension gradients, 26−28 are ubiquitous and have been proposed to explain swimming particles, 29 droplets, 30 and even insect locomotion. 31 Among previous laboratory studies, three of them are most notable when considering the work we report here.…”

Section: ■ Introductionmentioning

confidence: 99%

Volatile Droplets on Water are Sculpted by Vigorous Marangoni-Driven Subphase Flow

Li,

Chen,

et al. 2023

Langmuir

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The shapes of highly volatile oil-on-water droplets become strongly asymmetric when they are out of equilibrium. The unsaturated organic vapor atmosphere causes evaporation and leads to a strong Marangoni flow in the bath, unlike that previously seen in the literature. Inspecting these shapes experimentally on millisecond and submillimeter time and length scales and theoretically by scaling arguments, we confirm that Marangonidriven convection in the subphase mechanically stresses the droplet edges to an extent that increases for organic droplets of smaller contact angle and accordingly smaller thickness. The viscous stress generated by the subphase overcomes the thermodynamic Laplace pressure. The oil droplets develop copious regularly spaced fingers, and these fingers develop spike-shaped and branched treelike structures. Unlike this behavior for single-component (surfactant-free) oil droplets, droplets composed of two miscible (surfactant-free) organic liquids develop a rim of the less volatile component along the droplet perimeter, from which jets of monodisperse smaller droplets eject periodically due to the Rayleigh−Plateau instability. When evaporation shrinks droplets to μm size, their shapes fluctuate chaotically, and ellipsoidal shapes rupture into smaller daughter droplets when subphase convection flow pulls them in opposite directions. The shape of the evaporating oil droplets is kneaded and sculpted by vigorous flow in the water subphase.

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Functional liquid droplets for analyte sensing and energy harvesting

Cited by 8 publications

References 142 publications

Liquid–Polymer Contact Electrification: Modeling the Dependence of Surface Charges and ξ-Potential on pH and Added-Salt Concentration

Liquid–Polymer Contact Electrification: Modeling the Dependence of Surface Charges and ξ-Potential on pH and Added-Salt Concentration

Dry‐Spinning of Artificial Spider Silk Ribbons From Regenerated Natural Spidroin in an Organic Medium

Volatile Droplets on Water are Sculpted by Vigorous Marangoni-Driven Subphase Flow

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