scholarly journals Breakup Dynamics of Semi-dilute Polymer Solutions in a Microfluidic Flow-focusing Device

Micromachines ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 406
Author(s):  
Chun-Dong Xue ◽  
Xiao-Dong Chen ◽  
Yong-Jiang Li ◽  
Guo-Qing Hu ◽  
Tun Cao ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Polymer Solutions ◽  
Newtonian Fluids ◽  
Droplet Microfluidics ◽  
Droplet Generation ◽  
Flow Focusing ◽  
Polymeric Fluids ◽  
Practical Applications ◽  
Dilute Polymer Solutions ◽  
Microfluidic Flow

Droplet microfluidics involving non-Newtonian fluids is of great importance in both fundamental mechanisms and practical applications. In the present study, breakup dynamics in droplet generation of semi-dilute polymer solutions in a microfluidic flow-focusing device were experimentally investigated. We found that the filament thinning experiences a transition from a flow-driven to a capillary-driven regime, analogous to that of purely elastic fluids, while the highly elevated viscosity and complex network structures in the semi-dilute polymer solutions induce the breakup stages with a smaller power-law exponent and extensional relaxation time. It is elucidated that the elevated viscosity of the semi-dilute solution decelerates filament thinning in the flow-driven regime and the incomplete stretch of polymer molecules results in the smaller extensional relaxation time in the capillary-driven regime. These results extend the understanding of breakup dynamics in droplet generation of non-Newtonian fluids and provide guidance for microfluidic synthesis applications involving dense polymeric fluids.

Non-Newtonian Droplet Generation in a Flow-Focusing Microchannel

2019 ◽  
Author(s):  
C. D. Xue ◽  
Z. P. Sun ◽  
Y. J. Li ◽  
K. R. Qin
Keyword(s):  
Polyethylene Oxide ◽  
Food Production ◽  
Continuous Phase ◽  
Droplet Microfluidics ◽  
Droplet Generation ◽  
Flow Focusing ◽  
Complete Understanding ◽  
Practical Applications ◽  
Primary Droplet ◽  
Newtonian Behavior

Abstract The emergence of microfluidic droplets offers new opportunities to advance biomedical engineering, food production, and energy storage applications. These applications always involve complex fluids exhibiting obvious non-Newtonian behavior. Droplet generation has been extensively addressed, while the complete understanding of droplet generation in non-Newtonian fluid system is still nascent. Here, we present the study of non-Newtonian droplet generation in a flow-focusing microchannel. Polyethylene oxide aqueous solutions are used as the dispersed phase, while olive oil serves as the continuous phase to induce the generation. The molecular weight of polymer is constant while the concentrations are varied from dilute to semi-dilute regimes that are rarely explored in existing studies. The main features of non-Newtonian droplet generation are first identified, after which the concentration-dependent dripping to jetting transitions are clarified. The effects of shear thinning and elasticity on droplet generation are then separately investigated. We finally propose a scaling relation to predict the primary droplet size with the satellite droplets neglected. These results can not only extend the fundamental theory of droplet microfluidics but also facilitate the practical applications.

scholarly journals Negative Pressure Provides Simple and Stable Droplet Generation in a Flow-Focusing Microfluidic Device

Micromachines ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 662
Author(s):  
Nikita A. Filatov ◽  
Anatoly A. Evstrapov ◽  
Anton S. Bukatin
Keyword(s):  
Microfluidic Device ◽  
Negative Pressure ◽  
Low Cost ◽  
Control Valve ◽  
Droplet Microfluidics ◽  
Droplet Generation ◽  
Electric Signal ◽  
Absolute Pressure ◽  
Flow Focusing ◽  
Wide Range

Droplet microfluidics is an extremely useful and powerful tool for industrial, environmental, and biotechnological applications, due to advantages such as the small volume of reagents required, ultrahigh-throughput, precise control, and independent manipulations of each droplet. For the generation of monodisperse water-in-oil droplets, usually T-junction and flow-focusing microfluidic devices connected to syringe pumps or pressure controllers are used. Here, we investigated droplet-generation regimes in a flow-focusing microfluidic device induced by the negative pressure in the outlet reservoir, generated by a low-cost mini diaphragm vacuum pump. During the study, we compared two ways of adjusting the negative pressure using a compact electro-pneumatic regulator and a manual airflow control valve. The results showed that both types of regulators are suitable for the stable generation of monodisperse droplets for at least 4 h, with variations in diameter less than 1 µm. Droplet diameters at high levels of negative pressure were mainly determined by the hydrodynamic resistances of the inlet microchannels, although the absolute pressure value defined the generation frequency; however, the electro-pneumatic regulator is preferable and convenient for the accurate control of the pressure by an external electric signal, providing more stable pressure, and a wide range of droplet diameters and generation frequencies. The method of droplet generation suggested here is a simple, stable, reliable, and portable way of high-throughput production of relatively large volumes of monodisperse emulsions for biomedical applications.

Surface-tension-driven breakup of viscoelastic liquid threads

1982 ◽  
Vol 120 ◽  
pp. 245-266 ◽  
Author(s):  
Simon L. Goren ◽  
Moshe Gottlieb
Keyword(s):  
Relaxation Time ◽  
Stress Relaxation ◽  
Polymer Solutions ◽  
Small Diameter ◽  
Shear Thinning ◽  
Prior History ◽  
Axial Tension ◽  
Dilute Polymer Solutions ◽  
Linearized Stability ◽  
Newtonian Liquids

A linearized stability analysis is carried out for the breakup of small-diameter liquid filaments of dilute polymer solutions into droplets. Oldroyd's 8-constant model expressed in a corotational reference frame is used as the rheological equation of state. The crucial idea in this theory is the recognition that the liquid may be subject to an unrelaxed axial tension due to its prior history. If the tension is zero, the present analysis predicts that jets of shear-thinning liquids are less stable than comparable jets of Newtonian liquids; this is in agreement with previous analyses. However, when the axial tension is not zero, and provided the stress relaxation time constant is sufficiently large, the new theory predicts that the axial elastic tension can be a significant stabilizing influence. With reasonable values for the tension and stress relaxation time the theory explains the great stability observed for jets of some shear- thinning, dilute polymer solutions. The theory explains why drops produced from jets of such liquids are larger than drops from corresponding Newtonian liquids. The theory also appears capable of explaining the sudden appearance of irregularly spaced bulges on jets after long distances of t,ravel with little amplification of disturbances.

scholarly journals The laminar flow of dilute polymer solutions around circular cylinders

1970 ◽  
Vol 42 (2) ◽  
pp. 269-288 ◽  
Author(s):  
David F. James ◽  
Allan J. Acosta
Keyword(s):  
Heat Transfer ◽  
Relaxation Time ◽  
Polymer Solutions ◽  
Fluid Velocity ◽  
Maxwell Model ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Dimensionless Group ◽  
Number Range ◽  
Dilute Polymer Solutions

This paper describes the measurements of heat transfer and drag for the flow of dilute polymer solutions around very small cylinders. The thermal experiments were carried out at Reynolds numbers less than 50, and the results establish the dependence of the heat transfer on fluid velocity, cylinder diameter, solution concentration, and polymer molecular weight. The drag measurements were conducted with the same type of solutions and in the same Reynolds-number range. To complement the heat-transfer and drag measurements, the flows around a cylinder and through an orifice were examined visually. These flow-visualization studies showed that the streamline pattern with dilute polymer solutions can be significantly different from that with Newtonian fluids because of viscoelastic effects.An analysis of Rouse's theory of macromolecules shows that for low accelerations a dilute polymer solution behaves mechanically like a Maxwell model. The analysis thereby produces a relaxation time, a single parameter representing the elasticity of the fluid, which can be related to the properties of the solute and solvent. This relaxation time is contained in a new dimensionless group which governs dynamic similarity when induced elastic stresses dominate viscous stresses in the flow around a circular cylinder. The dimensionless group is shown to correlate the thermal data when the heat transfer does not depend on the free stream velocity.

Energy transfer in turbulent polymer solutions

2007 ◽  
Vol 581 ◽  
pp. 419-436 ◽  
Author(s):  
C. M. CASCIOLA ◽  
E. DE ANGELIS
Keyword(s):  
Polymer Solutions ◽  
Classical Method ◽  
Physical Space ◽  
Free Energy Density ◽  
Turbulence Theory ◽  
Spectral Space ◽  
Micro Structure ◽  
Polymeric Fluids ◽  
Dilute Polymer Solutions ◽  
Polymeric Chains

The paper addresses a set of new equations concerning the scale-by-scale balance of turbulent fluctuations in dilute polymer solutions. The main difficulty is the energy associated with the polymers, which is not of a quadratic form in terms of the traditional descriptor of the micro-structure. A different choice is however possible, which, at least for mild stretching of the polymeric chains, directly leads to an L2 structure for the total free-energy density of the system thus allowing the extension of the classical method to polymeric fluids. On this basis, the energy budget in spectral space is discussed, providing the spectral decomposition of the energy of the system. New equations are also derived in physical space, to provide balance equations for the fluctuations in both the kinetic field and the micro-structure, thus extending, in a sense, the celebrated Kármán–Howarth and Kolmogorov equations of classical turbulence theory. The paper is limited to the context of homogeneous turbulence. However the necessary steps required to expand the treatment to wall-bounded flows of polymeric liquids are indicated in detail.

Electrowetting-controlled droplet generation in a microfluidic flow-focusing device

2007 ◽  
Vol 19 (46) ◽  
pp. 462101 ◽  
Author(s):  
Florent Malloggi ◽  
Siva A Vanapalli ◽  
Hao Gu ◽  
Dirk van den Ende ◽  
Frieder Mugele
Keyword(s):  
Droplet Generation ◽  
Flow Focusing ◽  
Microfluidic Flow
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