Active Brownian motion of emulsion droplets: Coarsening dynamics at the interface and rotational diffusion

Schmitt, Maximilian; Stark, Holger

doi:10.1140/epje/i2016-16080-y

Cited by 22 publications

(15 citation statements)

References 84 publications

(154 reference statements)

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“…5b) at t/∆t LB = 6×10 5 and fitted it by using Eq. (23). Although only on a qualitative level, our results support the view that the droplet behaves as pusher-like particle (regardless of the sign of B 1 ), as the propulsion acts mainly from the rear of the droplet [35,36,37].…”

Section: Self-propelled Dropletsupporting

confidence: 76%

Lattice Boltzmann study of chemically-driven self-propelled droplets

et al. 2017

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We numerically study the behavior of self-propelled liquid droplets whose motion is triggered by a Marangoni-like flow. This latter is generated by variations of surfactant concentration which affect the droplet surface tension promoting its motion. In the present paper a model for droplets with a third amphiphilic component is adopted. The dynamics is described by Navier-Stokes and convection-diffusion equations, solved by the lattice Boltzmann method coupled with finite-difference schemes. We focus on two cases. First, the study of self-propulsion of an isolated droplet is carried on and, then, the interaction of two self-propelled droplets is investigated. In both cases, when the surfactant migrates towards the interface, a quadrupolar vortex of the velocity field forms inside the droplet and causes the motion. A weaker dipolar field emerges instead when the surfactant is mainly diluted in the bulk. The dynamics of two interacting droplets is more complex and strongly depends on their reciprocal distance. If, in a head-on collision, droplets are close enough, the velocity field initially attracts them until a motionless steady state is achieved. If the droplets are vertically shifted, the hydrodynamic field leads to an initial reciprocal attraction followed by a scattering along opposite directions. This hydrodynamic interaction acts on a separation of some droplet radii otherwise it becomes negligible and droplets motion is only driven by the Marangoni effect. Finally, if one of the droplets is passive, this latter is generally advected by the fluid flow generated by the active one.

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Section: Self-propelled Dropletsupporting

confidence: 76%

Lattice Boltzmann study of chemically-driven self-propelled droplets

et al. 2017

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“…We use a finite volume discretization on a uniform grid. Accordingly, we tile the interface using roughly 56.000 to 127.000 hexagons (depending on the problem) and approximate all functions f by their values f i at the center x i of each cell i (similar to [50]). If we know f exactly, we approximate it by the spatial average over each cell i with area A.…”

Section: Numerical Solvermentioning

confidence: 99%

Feedback control of photoresponsive fluid interfaces

Grawitter

Stark

2018

Soft Matter

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Photoresponsive surfactants provide a unique microfluidic driving mechanism. Since they switch between two molecular shapes under illumination and thereby affect surface tension of fluid interfaces, Marangoni flow along the interface occurs. To describe the dynamics of the surfactant mixture at a planar interface, we formulate diffusion-advection-reaction equations for both surfactant densities. They also include adsorption from and desorption into the neighboring fluids and photoisomerization by light. We then study how the interface responds when illuminated by spots of light. Switching on a single light spot, the density of the switched surfactant spreads in time and assumes an exponentially decaying profile in steady state. Simultaneously, the induced radial Marangoni flow reverses its flow direction from inward to outward. We use this feature to set up specific feedback rules, which couple the advection velocities sensed at the light spots to their intensities. As a result two neighboring spots switch on and off alternately. Extending the feedback rule to light spots arranged on the vertices of regular polygons, we observe periodic switching patterns for even-sided polygons, where two sets of next-nearest neighbors alternate with each other. A triangle and pentagon also show regular oscillations, while heptagon and nonagon exhibit irregular oscillations due to frustration. While our findings are specific to the chosen set of parameters, they show how complex patterns at photoresponsive fluid interfaces emerge from simple feedback coupling.

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“…15 Brownian motion of the nanoemulsion droplets overcomes the influence of gravity, thus preventing separation and aggregation to greatly increase the stability. 32 Additionally, a large number of hydroxyl groups on the surface of EPS and PEG400 molecules cause steric hindrance between particles, which effectively restrict the free movement of particles to prevent particle coalescence. 33 Generally, the pH of the normal vaginal environment ranges between 3.8 and 4.5.…”

Section: Discussionmentioning

confidence: 99%

<p>Ultrasound-Assisted Preparation of Exopolysaccharide/Nystatin Nanoemulsion for Treatment of Vulvovaginal Candidiasis</p>

Song¹,

Fang²,

Cheng³

et al. 2020

IJN

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Purpose: As one of the classic anti-Canidia albicans (CA) and vulvovaginal candidiasis (VVC) drugs, nystatin (NYS) is limited by poor water solubility and easy aggregation. Traditional NYS vaginal delivery formulations do not fully adapt to the specific environment of the vaginal cavity. The use of exopolysaccharides (EPS) has great application potential in emulsifiers, but its use has not been reported in nanoemulsions. In this work, an EPS/NYS nanoemulsion (ENNE) was developed to improve the activities of NYS against CA and VVC Methods: The ENNE was prepared by ultrasonic method using EPS as an emulsifier, liquid paraffin oil as an oil phase, PEG400 as a co-emulsifier, and NYS as the loaded drug. ENNE preparation was optimized by response surface method. After optimization, in vitro and in vivo analysis of the anti-CA activity; animal experiments; staining with propidium iodide (PI), periodic acid-schiff (PAS), and hematoxylin-eosin (H&E); and cytokine experiments were performed to investigate the therapeutic ability against VVC. Results: The optimal formulation and preparation parameters of ENNE were determined as follows: EPS content of 1.5%, PEG400 content of 3.2%, NYS content of 700 μg/mL, paraffin oil content of 5.0%, ultrasonic time of 15 min, and ultrasonic amplitude of 35%. The ENNE showed an encapsulated structure with an average particle size of 131.1 ± 4.32 nm. ENNE exhibited high storage and pH stability, as well as slow release. The minimum inhibitory concentration (MIC) of ENNE against CA was only 0.125 μg/mL and the inhibition zone was 19.0 ± 0.5 mm, for greatly improved anti-CA effect. The prepared ENNE destroyed the membrane of CA cells, and exhibited good anti-CA effect in vivo and therapeutic ability against VVC. Conclusion: The results of this study will promote the application of EPS in nanotechnology, which should lead to new and effective local drug formulations for treating VVC.

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Active Brownian motion of emulsion droplets: Coarsening dynamics at the interface and rotational diffusion

Cited by 22 publications

References 84 publications

Lattice Boltzmann study of chemically-driven self-propelled droplets

Lattice Boltzmann study of chemically-driven self-propelled droplets

Feedback control of photoresponsive fluid interfaces

<p>Ultrasound-Assisted Preparation of Exopolysaccharide/Nystatin Nanoemulsion for Treatment of Vulvovaginal Candidiasis</p>

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