Abstract:

The data being shared contains results of numerical simulations of the motion of a micro-swimmer (modeled as a force dipole) around a clean drop and a surfactant-laden drop. The study was performed to investigate the ability of drops to hydrodynamically attract a micro-swimmer onto their surfaces. The following data are included (all in dimensionless form): 1. The values of the critical trapping radius, i.e, the threshold drop radius above which a 'trapped' swimmer cannot escape from the drop's surface via hydrodynamics alone. 2. The values of the depth of the basin of attraction, i.e., the maximum distance from the surface of the drop, for which a swimmer released tangentially to the drop gets attracted to it, and begins to orbit around it. 3. The empirical distribution of the trapping time of micro-swimmers - who, unlike the previous two cases, can also perform 'diffusion-based' motion - released tangentially to the drop at a separation less than the depth of the basin of attraction. Each of these datasets will be provided for different values of the viscosity ratio (of the drop with respect to the suspending fluid), the dimensionless surface viscosity of the drop (this is applicable only for surfactant-laden drops), and the dimensionless dipole strength of the micro-swimmer.

Suggested Citation:

Nikhil Desai, Vaseem A. Shaik, Arezoo M. Ardekani. 2018. Dataset for: Hydrodynamics-mediated trapping of micro-swimmers near drops. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N71Z42VX

Publications:

Desai, N., Shaik, V. A., & Ardekani, A. M. (2018). Hydrodynamics-mediated trapping of micro-swimmers near drops. Soft Matter, 14(2), 264–278. doi:10.1039/c7sm01615h

Purpose:

The data was produced with an aim to understand the swimming motion of a model micro-swimmer (a force dipole) in the vicinity of clean and surfactant-laden drops. It has potential implications in understanding the hydrodynamic attraction - a passive mechanism for microbe accumulation near fluid-fluid interfaces - of micro-organisms to oil drops. The data sheds light on the role of surfactant/dispersant addition in scenarios involving spillage of insoluble hydrocarbons.

Data Parameters and Units:

All the data are reported in the form of dimensionless numbers. The lengths are normalized by the characteristic swimmer length scale 'b'; the speeds are normalized by the characteristic swimming speed of the micro-swimmer 'V_s'; the time is normalized by the characteristic time scale 't_ref', given by, t_ref = b/V_s. Data included: (i) different values of the viscosity ratio (defined by the symbol '\lambda') for the case of a clean drop; (ii) different values of the viscosity ratio and the dimensionless surface viscosity (defined by the symbol '\beta') for the case of a surfactant-laden drop; and (iii) different values of the dimensionless dipole strength (defined by the symbol '\alpha') of the micro-swimmer. The viscosity ratio is defined as: \lambda = \mu_i/\mu_e, where '\mu_i' and '\mu_e' denote the viscosity of the fluid inside and outside the drop. The dimensionless interfacial viscosity is defined as: \beta = \mu_s/(\mu_e*a), where '\mu_s' and 'a' are the interfacial viscosity and the radius of the drop, respectively. Note that the concept of the interfacial viscosity is applicable only for a surfactant-laden drop and not for a clean drop. The dimensionless dipole strength is defined as: \alpha = F/(8*\pi*\mu_e*b^2*V_s), where 'F' is the micro-swimmer's dimensional dipole strength (SI units of 'F' -> Newton-meter), while the other parameters have been defined in the previous paragraphs.

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