Computational studies of shear-dependent non-newtonian droplet formation at microfluidics T-junction with experimental justification

When Reynolds number (Re) is typically small, the dominant forces governing droplet formation in a microfluidic system includes surface tension, viscous, adhesion, and inertial forces, and the rheology of fluid becomes significantly important when non-Newtonian fluids are involved. The aim of this thesis is to systematically investigate the non-Newtonian shear-thinning effect of sodium carboxymethylcellulose (CMC) on the physical process of droplet formation. A two-phase conservative level-set formulation is adopted to capture the droplets breakup dynamics and relevant hydrodynamics. Detailed two-dimensional (2D) computational microfluidics flow simulations were carried out to examine systematically the influence of different controlling parameters such as degree of shear-thinning (ηo/η∞), relaxation time (λCY), flow rates (Qc, Qd), viscosities (ηc, ηd), surface wettability (θ), and interfacial tensions (σ) on CMC microdroplets formation in a Newtonian continuum. Experimental tests and numerical model justification were performed in conjunction with grid refinement to support the computational analysis and ensure its accuracy and numerical stability. The breakup process of CMC microdroplets in the cross-flowing immiscible liquids in microfluidic device with T-shaped geometry was predicted well. Data for the rheological and physical properties obeying the Carreau-Yasuda stress model were experimentally obtained to support the computational work. In present study, it is worth noting that the dynamics of shear-thinning breakup process is very sensitive to the rheological quantities (ηo/η∞, λCY) under a range of typical shear rate that associated with microchannel. The systematic variation in these rheological quantities has demonstrated different velocity profile and droplet properties. This variation significantly affects the size of droplet and breakup regime, which has never been studied previously. In contrast to previous findings based on Newtonian solutions, the dependence of flow regimes, breakup time and generation frequency on CMC polymer concentration is distinctly different in dilute and semi-dilute concentration regimes, which only exists in polymer solutions. In dilute regimes, the breakup dynamics is similar to pure Newtonian solutions, which is droplet breakup sharply at the corner of T-Junction, as the polymers are at sufficiently low concentration. Conversely, in semi-dilute regime, the presence of highly polymer molecules leads to an elongated fluid thread, a delay in breakup time, and lower production rate of droplet. Interestingly, the existence of thin polymeric filament can be observed prior to breakup for shear-thinning solution. This feature is rarely observed in Newtonian solution, but a similar phenomenon that was previously attributed to elastic effects in the fluid. Besides, the instabilities in the filament leading to the formation and breakup of satellite droplets. In the view of essential role of interfacial tension, adhesion, viscous and inertial forces, the size of shear-thinning CMC droplets is always found to be smaller than the size of Newtonian droplets as it is believed that the shear-thinning thread encounter less resistance, resulting in rapid breakup phenomenon. Present investigations enhance the understanding of the polymer structural features that govern the droplet behaviour in different flow condition. This may contributes a conceptual framework to rheological application in pharmaceutical field, especially drug delivery system, which focuses on the stability and diffusion of drug particles in dispersion into the outer fluid

Computational studies of shear-dependent non-newtonian droplet formation at microfluidics T-junction with experimental justification

When Reynolds number (Re) is typically small, the dominant forces governing droplet formation in a microfluidic system includes surface tension, viscous, adhesion, and inertial forces, and the rheology of fluid becomes significantly important when non-Newtonian fluids are involved. The aim of this thesis is to systematically investigate the non-Newtonian shear-thinning effect of sodium carboxymethylcellulose (CMC) on the physical process of droplet formation. A two-phase conservative level-set formulation is adopted to capture the droplets breakup dynamics and relevant hydrodynamics. Detailed two-dimensional (2D) computational microfluidics flow simulations were carried out to examine systematically the influence of different controlling parameters such as degree of shear-thinning (ηo/η∞), relaxation time (λCY), flow rates (Qc, Qd), viscosities (ηc, ηd), surface wettability (θ), and interfacial tensions (σ) on CMC microdroplets formation in a Newtonian continuum. Experimental tests and numerical model justification were performed in conjunction with grid refinement to support the computational analysis and ensure its accuracy and numerical stability. The breakup process of CMC microdroplets in the cross-flowing immiscible liquids in microfluidic device with T-shaped geometry was predicted well. Data for the rheological and physical properties obeying the Carreau-Yasuda stress model were experimentally obtained to support the computational work. In present study, it is worth noting that the dynamics of shear-thinning breakup process is very sensitive to the rheological quantities (ηo/η∞, λCY) under a range of typical shear rate that associated with microchannel. The systematic variation in these rheological quantities has demonstrated different velocity profile and droplet properties. This variation significantly affects the size of droplet and breakup regime, which has never been studied previously. In contrast to previous findings based on Newtonian solutions, the dependence of flow regimes, breakup time and generation frequency on CMC polymer concentration is distinctly different in dilute and semi-dilute concentration regimes, which only exists in polymer solutions. In dilute regimes, the breakup dynamics is similar to pure Newtonian solutions, which is droplet breakup sharply at the corner of T-Junction, as the polymers are at sufficiently low concentration. Conversely, in semi-dilute regime, the presence of highly polymer molecules leads to an elongated fluid thread, a delay in breakup time, and lower production rate of droplet. Interestingly, the existence of thin polymeric filament can be observed prior to breakup for shear-thinning solution. This feature is rarely observed in Newtonian solution, but a similar phenomenon that was previously attributed to elastic effects in the fluid. Besides, the instabilities in the filament leading to the formation and breakup of satellite droplets. In the view of essential role of interfacial tension, adhesion, viscous and inertial forces, the size of shear-thinning CMC droplets is always found to be smaller than the size of Newtonian droplets as it is believed that the shear-thinning thread encounter less resistance, resulting in rapid breakup phenomenon. Present investigations enhance the understanding of the polymer structural features that govern the droplet behaviour in different flow condition. This may contributes a conceptual framework to rheological application in pharmaceutical field, especially drug delivery system, which focuses on the stability and diffusion of drug particles in dispersion into the outer fluid

Microdroplets Advancement in Newtonian and Non- Newtonian Microfluidic Multiphase System

With recent advancement in droplet microfluidics for both microdroplet encapsulation and fission, it is of paramount importance to understand the flow physics for both Newtonian and non-Newtonian fluids in microdroplet encapsulation and fission as the development of the field is approaching to its maturity. The chapter aims to review and discuss the fluid flow behavior of the multiphase system, mathematical models as well as the fundamental phenomena driving force of microdroplet encapsulation and fission multiphase system. Together, the recent advances in technologies that enable fabrication and application of droplets encapsulation and fission from both Newtonian and non-Newtonian microfluidic multiphase system will be reviewed as well

Microfluidic Synthesis of Functional Materials as Potential Sorbents for Water Remediation and Resource Recovery

The advance of droplet-based microfluidics has enabled compartmentalization and controlled manipulation of monodispersed emulsions with high yield and incorporation efficiency. It has become a highly exotic platform in synthesizing functional material due to the presence of two immiscible liquids and the interface between them. With its intrinsic feature in high degree of product control, advanced emulsion-based synthesis of functional material is constituted as a template for effective water remediation and resource recovery. This chapter aims to provide an overview of recent advances in microfluidic technology for environmental remediation. More specifically, the facility of microemulsion-based functional materials for water remediation is reviewed. Moreover, the removal and recovery of pollutants, such as heavy metal, dye, pharmaceuticals, etc., from aquatic environment by the applications of adsorption on functional micro/nanomaterials are unfolded with respect to its potential for wastewater purification

Numerical studies of shear-thinning droplet formation in a microfluidic T-junction using two-phase level-set method

A conservative level-set method (LSM) embedded in a computational fluid dynamics (CFD) simulation provides a useful approach for the studying the physics and underlying mechanism in two-phase flow. Detailed two-dimensional (2D) computational microfluidics flow simulations have been carried out to examine systematically the influence of different controlling parameters such as flow rates, viscosities, surface wettability, and interfacial tensions between two immiscible fluids on the non-Newtonian shear-thinning microdroplets generation process. For the two-phase flow system that neglects the Marangoni effect, the breakup process of shear-thinning microdroplets in cross-flowing immiscible liquids in a microfluidic device with a T-shaped geometry was predicted. Data for the rheological and physical properties of fluids obeying Carreau-Yasuda stress model were empirically obtained to support the computational work. The simulation results show that the relevant control parameters mentioned above have a strong impact on the size of shear-thinning droplets generated. Present computational studies on the role and relative importance of controlling parameters can be established as a conceptual framework of the non-Newtonian droplet generation process and relevant phenomena for future studies

Nanoemulsions - Properties, Fabrications and Applications

Fluidics, an increasingly examined topic in nanoscience and nanotechnology is often discussed with regard to the handling of fluid flow, material processing, and material synthesis in innovative devices ranging from the macroscale to the nanoscale. Nanoemulsions - Properties, Fabrications and Applications reviews key concepts in nanoscale fluid mechanics, its corresponding properties, as well as the latest trends in nanofluidics applications. With attention to the fundamentals as well as advanced applications of fluidics, this book imparts a solid knowledge base and develops skill for future problem-solving and system analysis. This is a vital resource for upper-level engineering students who want to expand their potential career opportunities and familiarize themselves with an increasingly important field