The effect of surface charge convection and shape deformation on the settling velocity of drops in nonuniform electric field

2017 ◽  
Vol 29 (1) ◽  
pp. 012101 ◽  
Author(s):  
Shubhadeep Mandal ◽  
Aditya Bandopadhyay ◽  
Suman Chakraborty
Keyword(s):  
Electric Field ◽  
Surface Charge ◽  
Settling Velocity ◽  
Nonuniform Electric Field ◽  
Shape Deformation ◽  
Effect Of Surface

scholarly journals Uniform electric-field-induced lateral migration of a sedimenting drop

2016 ◽  
Vol 792 ◽  
pp. 553-589 ◽  
Author(s):  
Aditya Bandopadhyay ◽  
Shubhadeep Mandal ◽  
N. K. Kishore ◽  
Suman Chakraborty
Keyword(s):  
Electric Field ◽  
Surface Charge ◽  
Tilt Angle ◽  
Shape Deformation ◽  
Uniform Electric Field ◽  
Lateral Motion ◽  
Drop Surface ◽  
Lateral Migration ◽  
Drop Velocity ◽  
Pressure Fields

We investigate the motion of a sedimenting drop in the presence of an electric field in an arbitrary direction, otherwise uniform, in the limit of small interface deformation and low-surface-charge convection. We analytically solve the electric potential in and around the leaky dielectric drop, and solve for the Stokesian velocity and pressure fields. We obtain the correction in drop velocity due to shape deformation and surface-charge convection considering small capillary number and small electric Reynolds number which signifies the importance of charge convection at the drop surface. We show that tilt angle, which quantifies the angle of inclination of the applied electric field with respect to the direction of gravity, has a significant effect on the magnitude and direction of the drop velocity. When the electric field is tilted with respect to the direction of gravity, we obtain a non-intuitive lateral motion of the drop in addition to the buoyancy-driven sedimentation. Both the charge convection and shape deformation yield this lateral migration of the drop. Our analysis indicates that depending on the magnitude of the tilt angle, conductivity and permittivity ratios, the direction of the sedimenting drop can be controlled effectively. Our experimental investigation further confirms the presence of lateral migration of the drop in the presence of a tilted electric field, which is in support of the essential findings from the analytical formalism.

The effect of surface-charge convection on the settling velocity of spherical drops in a uniform electric field

2016 ◽  
Vol 797 ◽  
pp. 536-548 ◽  
Author(s):  
Ehud Yariv ◽  
Yaniv Almog
Keyword(s):  
Difference Equation ◽  
Electric Field ◽  
Surface Charge ◽  
Settling Velocity ◽  
Numerical Solutions ◽  
Weak Field ◽  
Uniform Electric Field ◽  
Electrostatic Problem ◽  
Settling Speed ◽  
The Difference

The mechanism of surface-charge convection, quantified by the electric Reynolds number $Re$, renders the Melcher–Taylor electrohydrodynamic model inherently nonlinear, with the electrostatic problem coupled to the flow. Because of this nonlinear coupling, the settling speed of a drop under a uniform electric field differs from that in its absence. This difference was calculated by Xu & Homsy (J. Fluid Mech., vol. 564, 2006, pp. 395–414) assuming small $Re$. We here address the same problem using a different route, considering the case where the applied electric field is weak in the sense that the magnitude of the associated electrohydrodynamic velocity is small compared with the settling velocity. As convection is determined at leading order by the well-known flow associated with pure settling, the electrostatic problem becomes linear for arbitrary value of $Re$. The electrohydrodynamic correction to the settling speed is then provided as a linear functional of the electric-stress distribution associated with that problem. Calculation of the settling speed eventually amounts to the solution of a difference equation governing the respective coefficients in a spherical harmonics expansion of the electric potential. It is shown that, despite the present weak-field assumption, our model reproduces the small-$Re$ approximation of Xu and Homsy as a particular case. For finite $Re$, inspection of the difference equation reveals a singularity at the critical $Re$-value $4S(1+R)(1+M)/(1+S)M$, wherein $R$, $S$ and $M$ respectively denote the ratios of resistivity, permittivity and viscosity values in the suspending and drop phases, as defined by Melcher & Taylor (Annu. Rev. Fluid Mech., vol. 1, 1969, pp. 111–146). Straightforward numerical solutions of this equation for electric Reynolds numbers smaller than the critical value reveal a non-monotonic dependence of the settling speed upon the electric field magnitude, including a transition from velocity enhancement to velocity decrement.

scholarly journals EFFECTS OF POLYMERIC NANOPARTICLE SURFACE PROPERTIES ON INTERACTION WITH BRAIN TUMOR ENVIRONMENT

Nano LIFE ◽  
2013 ◽  
Vol 03 (04) ◽  
pp. 1343003 ◽  
Author(s):  
BRANDON MATTIX ◽  
THOMAS MOORE ◽  
OLGA UVAROV ◽  
SAMUEL POLLARD ◽  
LAUREN O'DONNELL ◽  
...  
Keyword(s):  
Human Brain ◽  
Surface Charge ◽  
Cellular Uptake ◽  
Drug Clearance ◽  
Cellular Interaction ◽  
Normal Tissues ◽  
Poly Ethylene ◽  
Uptake Studies ◽  
Effect Of Surface

Current chemotherapy treatments are limited by poor drug solubility, rapid drug clearance and systemic side effects. Additionally, drug penetration into solid tumors is limited by physical diffusion barriers [e.g., extracellular matrix (ECM)]. Nanoparticle (NP) blood circulation half-life, biodistribution and ability to cross extracellular and cellular barriers will be dictated by NP composition, size, shape and surface functionality. Here, we investigated the effect of surface charge of poly(lactide)-poly(ethylene glycol) NPs on mediating cellular interaction. Polymeric NPs of equal sizes were used that had two different surface functionalities: negatively charged carboxyl ( COOH ) and neutral charged methoxy ( OCH 3). Cellular uptake studies showed significantly higher uptake in human brain cancer cells compared to noncancerous human brain cells, and negatively charged COOH NPs were uptaken more than neutral OCH 3 NPs in 2D culture. NPs were also able to load and control the release of paclitaxel (PTX) over 19 days. Toxicity studies in U-87 glioblastoma cells showed that PTX-loaded NPs were effective drug delivery vehicles. Effect of surface charge on NP interaction with the ECM was investigated using collagen in a 3D cellular uptake model, as collagen content varies with the type of cancer and the stage of the disease compared to normal tissues. Results demonstrated that NPs can effectively diffuse across an ECM barrier and into cells, but NP mobility is dictated by surface charge. In vivo biodistribution of OCH 3 NPs in intracranial tumor xenografts showed that NPs more easily accumulated in tumors with less collagen. These results indicate that a robust understanding of NP interaction with various tumor environments can lead to more effective patient-tailored therapies.

Breakdown of gas gaps in a nonuniform electric field at a subnanosecond voltage pulse rise time

2013 ◽  
Vol 58 (3) ◽  
pp. 370-374 ◽  
Author(s):  
A. M. Boichenko ◽  
V. F. Tarasenko ◽  
E. Kh. Baksht ◽  
A. G. Burachenko ◽  
M. V. Erofeev ◽  
...  
Keyword(s):  
Electric Field ◽  
Rise Time ◽  
Voltage Pulse ◽  
Nonuniform Electric Field ◽  
Pulse Rise Time

Electrostatic Dispensing of Dry Dielectric Materials

2001 ◽  
Vol 700 ◽  
Author(s):  
Malinda M. Tupper ◽  
Marjorie E. Chopinaud ◽  
Takamichi Ogawa ◽  
Michael J. Cima
Keyword(s):  
Electric Field ◽  
Field Intensity ◽  
Electric Field Intensity ◽  
Dielectric Materials ◽  
Nonuniform Electric Field ◽  
Sodium Fluorescein ◽  
Silica Spheres ◽  
Electrode Geometry ◽  
Wide Range ◽  
Silica Beads

AbstractDispensing micron-scale dielectric materials can be achieved through the use of dielectrophoresis. Electrodes are designed to create a nonuniform electric field. This method is expected to be applicable for transfer of a wide range of dielectric powders as well as small, shaped components. Small, 150 μm diameter silica spheres, as well as sodium fluorescein powder have been dispensed by this method. Selecting the appropriate electrode geometry and electric field intensity controls the amount collected. As little as 1.0 μg of sodium fluorescein powder, and as much as 16 mg of silica beads have been collected, and repeatability within 10 % of the total amount dispensed has been achieved.

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