Droplet shape relaxation in a four-channel microfluidic hydrodynamic trap

Narayan, Shweta; Moravec, Davis B.; Dallas, Andrew J.; Dutcher, Cari S.

doi:10.1103/physrevfluids.5.113603

Cited by 18 publications

(15 citation statements)

References 95 publications

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“…The flow in the channels is controlled by feedback control using a model predictive control (MPC) algorithm . Recently, this device was adapted by the authors’ group for droplet microfluidics by adding a T-junction droplet formation inlet upstream of the cross-slot to form a stream of monodisperse droplets. , Both droplet deformation and coalescence can be studied using this modified version of the Stokes trap. In this work, two sets of droplet coalescence measurements are discussed to illustrate the effect of the phase to which the surfactant is added and the effect of the viscosity ratio on interfacial mobility.…”

Section: Droplet Coalescence: Phase Dependence In Surfactant Systemsmentioning

confidence: 99%

Phase-Dependent Surfactant Transport on the Microscale: Interfacial Tension and Droplet Coalescence

2020

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Liquid−liquid emulsion systems are usually stabilized by additives, known as surfactants, which can be observed in various environments and applications such as oily bilgewater, water-entrained diesel fuel, oil production, food processing, cosmetics, and pharmaceuticals. One important factor that stabilizes emulsions is the lowered interfacial tension (IFT) between the fluid phases due to surfactants, inhibiting the coalescence. Many studies have investigated the surfactant transport behavior that leads to corresponding time-dependent lowering of the IFT. For example, the rate of IFT decay depends on the phase in which the surfactant is added (dispersed vs continuous) due in part to differences in the near-surface depletion depth. Other key factors, such as the viscosity ratio between the dispersed and continuous phases and Marangoni stress, will also have an impact on surfactant transport and therefore the coalescence and emulsion stability. In this feature article, the measurement techniques for dynamic IFT are first reviewed due to their importance in characterizing surfactant transport, with a specific focus on macroscale versus microscale techniques. Next, equilibrium isotherm models as well as dynamic diffusion and kinetic equations are discussed to characterize the surfactant and the time scale of the surfactant transport. Furthermore, recent studies are highlighted showing the different IFT decay rates and its long-time equilibrium value depending on the phase into which the surfactant is added, particularly on the microscale. Finally, recent experiments using a hydrodynamic Stokes trap to investigate the impact of interfacial surfactant transport, or "mobility", and the phase containing the surfactant on film drainage and droplet coalescence will be presented.

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Section: Droplet Coalescence: Phase Dependence In Surfactant Systemsmentioning

confidence: 99%

Phase-Dependent Surfactant Transport on the Microscale: Interfacial Tension and Droplet Coalescence

2020

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“…D is measured by varying the strain rate and droplet confinement at fixed viscosities and interfacial tension of fluids. A recent report has shown that droplet shape relaxation in the moderately confined regime exhibited strong dependence on the droplet radius but not on the ratio of dispersed to continuous phase viscosity [ 31 ]. We also observe that droplet deformation D increases with increasing droplet radius at fixed

( Figure 4 a).…”

Section: Resultsmentioning

confidence: 99%

“…Understanding the influence of confinement to the droplet deformation under homogeneous extensional flows will extend the utility of this approach to reveal droplet dynamics such as surfactant adsorption, droplet aging and transient interfacial dynamics. Recently, Narayan et al [ 31 ] studied the droplet shape relaxation in a four-channel microfluidic hydrodynamic trap in which they trapped and controlled the position of droplets using hydrodynamic forces and investigated the droplet shape relaxation after cessation of the pressure pulse. An empirical scaling relationship between the droplet shape relaxation and droplet radius was subsequently established and compared to the characteristic relaxation time for a droplet relaxing to equilibrium in a quiescent and infinite fluid reservoir.…”

Section: Introductionmentioning

confidence: 99%

Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

Lee

Shen

2021

Micromachines

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Droplet microfluidics provides a versatile tool for measuring interfacial tensions between two immiscible fluids owing to its abilities of fast response, enhanced throughput, portability and easy manipulations of fluid compositions, comparing to conventional techniques. Purely homogeneous extension in the microfluidic device is desirable to measure the interfacial tension because the flow field enables symmetric droplet deformation along the outflow direction. To do so, we designed a microfluidic device consisting of a droplet production region to first generate emulsion droplets at a flow-focusing area. The droplets are then trapped at a stagnation point in the cross junction area, subsequently being stretched along the outflow direction under the extensional flow. These droplets in the device are either confined or unconfined in the channel walls depending on the channel height, which yields different droplet deformations. To calculate the interfacial tension for confined and unconfined droplet cases, quasi-static 2D Darcy approximation model and quasi-static 3D small deformation model are used. For the confined droplet case under the extensional flow, an effective viscosity of the two immiscible fluids, accounting for the viscosity ratio of continuous and dispersed phases, captures the droplet deformation well. However, the 2D model is limited to the case where the droplet is confined in the channel walls and deforms two-dimensionally. For the unconfined droplet case, the 3D model provides more robust estimates than the 2D model. We demonstrate that both 2D and 3D models provide good interfacial tension measurements under quasi-static extensional flows in comparison with the conventional pendant drop method.

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“…The accuracy of the employed PIV algorithm has been previously exstensively assessed in literature (e.g., Guérin et al (2020), Vennemann and Rösgen (2020), Mohammadshahi et al (2020), Narayan et al (2020)). However, in order to ensure the physical consistency of our PIV measurements, two benchmark cases are here presented.…”

Section: Assessment Of Piv Chain Analysismentioning

confidence: 99%

A new dynamic masking technique for time resolved PIV analysis

Lombardi

Rocca

Prestininzi

2021

J Vis

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Time resolved PIV encompassing moving and/or deformable objects interfering with the light source requires the employment of dynamic masking (DM). A few DM techniques have been recently developed, mainly in microfluidics and multiphase flows fields. Most of them require ad-hoc design of the experimental setup, and may spoil the accuracy of the resulting PIV analysis. A new DM technique is here presented which envisages, along with a dedicated masking algorithm, the employment of fluorescent coating to allow for accurate tracking of the object. We show results from measurements obtained through a validated PIV setup demonstrating the need to include a DM step even for objects featuring limited displacements. We compare the proposed algorithm with both a no-masking and a static masking solution. In the framework of developing low cost, flexible and accurate PIV setups, the proposed algorithm is made available through a freeware application able to generate masks to be used by an existing, freeware PIV analysis package. Graphic abstract

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Droplet shape relaxation in a four-channel microfluidic hydrodynamic trap

Cited by 18 publications

References 95 publications

Phase-Dependent Surfactant Transport on the Microscale: Interfacial Tension and Droplet Coalescence

Phase-Dependent Surfactant Transport on the Microscale: Interfacial Tension and Droplet Coalescence

Interfacial Tension Measurements in Microfluidic Quasi-Static Extensional Flows

A new dynamic masking technique for time resolved PIV analysis

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