Drop impacts on electrospun nanofiber membranes

Sahu, Rakesh P.; Sinha-Ray, Suman; Yarin, Alexander L.; Pourdeyhimi, Behnam

doi:10.1039/c2sm06744g

Cited by 65 publications

(64 citation statements)

References 29 publications

(66 reference statements)

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“…This means that the pores hardly impose a significant hydraulic resistance. Nevertheless, due to a relatively high surface tension of blood (σ = 60.45 g/s 2 ), individual blood jets issued from the pores will immediately merge and form an intact layer, as observed in the experiments with high surface tension liquids in [38]. In distinction from [38], this intact liquid layer is subjected to tremendously high acceleration toward air and thus is prone to the Rayleigh-Taylor instability which sets an ultimate drop size.…”

Section: Resultsmentioning

confidence: 99%

“…Nevertheless, due to a relatively high surface tension of blood (σ = 60.45 g/s 2 ), individual blood jets issued from the pores will immediately merge and form an intact layer, as observed in the experiments with high surface tension liquids in [38]. In distinction from [38], this intact liquid layer is subjected to tremendously high acceleration toward air and thus is prone to the Rayleigh-Taylor instability which sets an ultimate drop size. Note also that when a target sponge is covered by tape or silicone (not the case in the present work), the blood spatter can be affected causing an uneven distribution of drops [19].…”

Section: Resultsmentioning

confidence: 99%

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Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis

2017

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A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the target (and perforated by the bullet) is predicted and compared with experimental data. The experimental data were acquired with a porous polyurethane foam sheet target impregnated with swine blood, and the blood drops were collected on a vertical cardstock sheet which was perforated by the blunt bullet. The highly porous target possesses a low hydraulic resistance and therefore resembles a pool of blood shot by a blunt bullet normally to its free surface. The back spatter pattern was predicted numerically and compared to the experimental data for the number of drops, their area, the total stain area, and the final impact angle as functions of radial location from the bullet hole in the cardstock sheet (the collection screen). Comparisons of the predicted results with the experimental data revealed satisfactory agreement. The predictions also allow one to find the impact Weber number on the collection screen, which is necessary to predict stain shapes and sizes. A theoretical model describing the blood spatter pattern resulting from a blunt bullet gunshot is proposed. The predictions are compared to experimental data acquired in the present work. This hydrodynamic problem belongs to the class of the impact hydrodynamics with the pressure impulse generating the blood flow. At the free surface, the latter is directed outwards and accelerated toward the surrounding air. As a result, the Rayleigh-Taylor instability of the flow of blood occurs, which is responsible for the formation of blood drops of different sizes and initial velocities. Thus, the initial diameter, velocity, and acceleration of the atomized blood drops can be determined. Then, the equations of motion are solved, describing drop trajectories in air accounting for gravity, and air drag. Also considered are the drop-drop interactions through air, which diminish air drag on the subsequent drops. Accordingly, deposition of two-phase (blood-drop and air) jets on a vertical cardstock sheet located between the shooter and the t...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis

2017

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“…Very low adhesion values were obtained in the case of coatings consisting of viscoelastic elastomers. Yarin and co‐workers reported a systematic study of drop impacts of polar and nonpolar liquids onto different electrospun nanofiber membranes with an increasing degree of hydrophobicity. It is found that for any liquid/fiber pair there exists a threshold impact velocity (≈1.5–3 m s −1 ) above which water penetrates membranes irrespective of their hydrophobicity.…”

Section: Introductionmentioning

confidence: 99%

Excellent Anti‐Icing Abilities of Optimal Micropillar Arrays with Nanohairs

Shi

Lei

Guo

et al. 2015

Adv Materials Inter

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of adhesion required to remove a liquid water drop. Poulikakos and co-workers [ 7 ] investigated surfaces with nanometerscale roughness and higher wettability, which display long freezing delays, one order of magnitude longer than typical superhydrophobic surfaces with larger hierarchical roughness and low wettability. And Poulikakos also established [ 8 ] that evaporative cooling of the supercooled liquid could engender ice crystallization by homogeneous nucleation at the droplet-free surface as opposed to the expected heterogeneous nucleation at the substrate. Hirayama and co-workers [ 9 ] investigated the icephobic properties of different coatings, e.g., hydrophilic and hydrophobic coatings, sol-gel based coatings containing fl uorinated compounds and viscoelastic rubbers. Very low adhesion values were obtained in the case of coatings consisting of viscoelastic elastomers. Yarin and co-workers [ 10 ] reported a systematic study of drop impacts of polar and nonpolar liquids onto different electrospun nanofi ber membranes with an increasing degree of hydrophobicity. It is found that for any liquid/fi ber pair there exists a threshold impact velocity (≈1.5-3 m s −1 ) above which water penetrates membranes irrespective of their hydrophobicity. Yarin and co-workers [ 11 ] studied peculiarities of drop impact onto electrospun polymer (polyacrylonitrile, PAN) nanofi ber mats. It is demonstrated that drop impacts on electrospun nanofi ber mats almost instantaneously result in spread-out wetted spots over the surface. All these researches above offer the foundation at different levels. However, it still remains a challenging how to further design the surface with superhydrophobic or anti-icing properties as surface in low temperature for a long time. [12][13][14][15][16][17] Here, we present a series of surfaces combined with nanohairs and micropillar arrays, i.e., different micropillar arrays with the similar nanohairs, different nanohairs with the same micropillar arrays. Especially, we reveal that the optimal surface with excellent abilities for anti-icing or antifogging is related with cooperation between superhydrophobic nanohairs and micropillar arrays, in addition to the stability of less liquid-solid fractions at low temperature below zero. This study will provide an insight into the design of structure size on micro-nanostructured surfaces for anti-icing/fogging ability effectively, with great significance that can be extended into the applications in some surfaces of systems, e.g., microdevices worked in cold or humid environment.Anti-icing abilities are achieved on surfaces of micropillar arrays with nanohairs that are fabricated by methods of soft replication and crystal growth, i.e., different micropillar arrays with the similar nanohairs, different nanohairs with the same micropillar arrays. It is demonstrated that an optimal micropillar array with nanohairs contributes an excellent anti-icing or antifogging property at low temperature below zero. As a result, the longest icing delay time is achieved effe...

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“…A requirement for this behaviour is that the solid surface be chemically heterogeneous so as to allow different distributions of chemical functional groups between those that are on the surface and those buried deeper in it. This effect is associated with a variety of phenomena including the marked differences between chemisorbed and physisorbed monolayers 7 and wetting transitions 8 with implications ranging from plant growth 9 through electrovariable optical components 10 to nanofiber membranes 11 , which are chemically heterogeneous.…”

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confidence: 99%

Water tribology on graphene

et al. 2012

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Classical experiments show that the force required to slide liquid drops on surfaces increases with the resting time of the drop, t rest , and reaches a plateau typically after several minutes. Here we use the centrifugal adhesion balance to show that the lateral force required to slide a water drop on a graphene surface is practically invariant with t rest . In addition, the drop's three-phase contact line adopts a peculiar micrometric serrated form. These observations agree well with current theories that relate the time effect to deformation and molecular reorientation of the substrate surface. Such molecular re-orientation is non-existent on graphene, which is chemically homogenous. Hence, graphene appears to provide a unique tribological surface test bed for a variety of liquid drop-surface interactions.

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Drop impacts on electrospun nanofiber membranes

Cited by 65 publications

References 29 publications

Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis

Hydrodynamics of back spatter by blunt bullet gunshot with a link to bloodstain pattern analysis

Excellent Anti‐Icing Abilities of Optimal Micropillar Arrays with Nanohairs

Water tribology on graphene

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