Interfacial viscosity-induced suppression of lateral migration of a surfactant laden droplet in a nonisothermal Poiseuille flow

Abstract

Understanding and modulating the cross-stream motion of a surfactant-coated droplet in pressure driven flow has great implications in many practical applications. A combination of interfacial viscosity and Marangoni stress acting over a surfactant-coated droplet in pressure driven flow offers greater flexibility to modulate the cross-stream motion of it. Despite the intense theoretical and numerical research towards manipulating the surfactant-laden Newtonian droplets in Poiseuille flow, the experimental investigations are seldom explored. Herein, we report our study on understanding the influence of interfacial viscosity on the cross-stream motion of a surfactantcoated Newtonian droplet in both isothermal and non-isothermal Poiseuille flow from a theoretical as well as an experimental perspective. A theoretical model has been developed to understand the effect of interfacial viscosity on the lateral migration of a droplet under the assumptions of no shape deformation and negligible fluid inertia or thermal convection. Theoretical analysis is performed under two limiting conditions: (i) when the transport of surfactants is dominated by surface-diffusion and (ii) when the transportation of surfactants is dominated by surface-convection. Our theoretical analysis shows that both the dilatational as well as the shear surface viscosities suppress the lateral migration velocity of the droplet. Experiments have been performed to validate the theoretically predicted droplet trajectories and to understand the influence of channel confinement on the lateral migration of the droplet. It has been observed from the experiments that the droplet travels faster towards the centerline of the flow in a highly confined domain. The results presented in this study could provide new vistas in designing and analyzing various droplet-based microfluidic, biomedical and bio-microfluidic devices.

Electric-field-mediated morpho-dynamic evolution in drop–drop coalescence phenomena in the inertio-capillary regime

“…From the early development of the subject, the dynamics of coalescence at drop-drop interfaces or drop-pool interfaces has been widely studied, in an effort to explain a plethora of natural phenomena such as the formation of mist, size variations of rain droplets in the atmosphere and fusion of raindrops into water reservoirs (Qian & Law 1997;Blanchette & Bigioni 2009;Tang, Zhang & Law 2012). In more recent years, there has been a growing interest in investigating the interactive dynamics of droplet arrays in engineered devices for manipulating various chemical and biological processes (Anna 2016;Sánchez Barea, Lee & Kang 2019;Panigrahi et al 2021;. Furthermore, in industrial applications like ink-jet printing, surface coating and fuel injectors, frequent events of drop collision appear inevitable (Aarts et al 2005;Tang et al 2012;Peng et al 2018;Varma et al 2020).…”

“…In more recent years, there has been a growing interest in investigating the interactive dynamics of droplet arrays in engineered devices for manipulating various chemical and biological processes (Anna 2016; Sánchez Barea, Lee & Kang 2019; Panigrahi et al. 2021; Santra & Chakraborty 2021). Furthermore, in industrial applications like ink-jet printing, surface coating and fuel injectors, frequent events of drop collision appear inevitable (Aarts et al.…”

Application of droplet migration scaling behavior to microchannel flow measurements

“…A general understanding of parametric dependency on droplet migration could be a useful tool in designing experimental studies. 27–29…”

“…A general understanding of parametric dependency on droplet migration could be a useful tool in designing experimental studies. [27][28][29] In this paper, we explore the feasibility of applying the margination scaling argument to polydisperse droplet emulsion experiments in steady state parabolic flow with varying conditions. We specifically compare theory to experimental techniques to study how droplets separate in a channel based on size, flow rate, volume fraction, and continuous phase viscosity.…”

Thermotactic navigation of an artificial microswimmer near a plane wall

“…In addition to self-phoresis, the application of an external temperature gradient was found to be advantageous in the creeping motion of droplets (Panigrahi et al. 2021; Mantripragada & Poddar 2022).…”