Modeling and simulation of micro/nano-rod distribution in micro channel flows

The behavior of a typical nanorod particle in microscale flows was theoretically investigated, considering the effect of the wall on the rotational and translation motions of the non-spherical particle. Initially, a systematic method using Brownian dynamics simulation of the rotational motion of nanorod was performed to obtain the average orientation distribution of a nanorod in various range of Peclet number and position from the confining wall. Subsequently, the results of the angle distributions simulation were employed to generate a universal mathematical model for the particle orientation distribution, which our model of concentration distribution of high aspect ratio nanorods in the microchannel was later built on. We identified three different rod-wall interaction mechanisms in the entire rages of Pe. Then, the model was extended to study low and high aspect ratio ellipsoidal nanorod particle separation in a Field Flow Fractionation channel. The model can describe the aspect ratio dependent elution behavior. In addition, Brownian dynamics simulation of microchannel separation of differently sized DNA chains driven by electrophoretic properties of DNA in an electric field was studied. COMSOL Multiphysics®, a popular science and engineering simulation software based on the finite element method, was used to perform the bead-spring dynamic simulation of the semi-flexible chain. The simulation results for DNA migration in an array of entropic traps were validated with the previous findings --Abstract, page iv

A Constitutive Model for Entangled Polydisperse Linear Flexible Polymers with Entanglement Dynamics and a Configuration Dependent Friction Coefficient. Part I: Model Derivation

A new polydisperse toy constitutive model is derived and developed from fundamental principles and ideas governing the nonlinear rheology of linear flexible polymers [Mead et al., J. Rheol. 59, 335-363 (2015)]. Specifically, the new model is comprised of four fundamental pieces. First, the model contains a simple differential description of the entanglement dynamics of discrete entanglement pairs. Second, the model contains a differential description of the ij entanglement pair orientation tensor dynamics. Third, following a similar development by Mead and Mishler [J. Non-Newtonian Fluid Mech. 197, 61-79 and 80-90 (2013).], a diluted stretch tube is constructed to describe the relative stretch of each component in the molecular weight distribution (MWD). Fourth, a description of configuration dependent friction coefficients is generated by generalizing the monodisperse formulation of Ianniruberto et al. [Macromolecules 45, 8058-8066 (2012)]. The polydisperse stress calculator is developed from the orientation, stretch and entanglement density and is fundamentally different from other molecular models that assume a constant entanglement density. The resulting model is comprised of three differential evolution equations and is simple to code and fast to execute. The model can simulate arbitrary fast nonlinear flows of arbitrary MWD\u27s. In the slow flow linear viscoelastic limit, the model collapses to the double reptation model. This welcome result has positive implications with respect to our model parameter determination [Ye et al., J. Rheol. 47, 443-468 (2003); Ye and Sridhar, Macromolecules 38, 3442-3449 (2005)] for making quantitative calculations

The Effect of Weak Confinement on the Orientation of Nanorods under Shear Flows

We performed a numerical analysis to study the orientation distribution of a dilute suspension of thin, rigid, rod-like nanoparticles under shearing flow near a solid boundary of weak confinement. Brownian dynamics simulation of a rod was performed under various ratios of shear rate and rod diffusivity (Peclet number), as well as the center-of-mass position (wall confinement). We discuss the effects of Peclet number and wall confinement on the angle distributions, Jeffery orbit distribution and average orientation moments. The average orientation moments, obtained as a function of Peclet number and wall confinement, can be used to improve a previous shear-induced migration model. We demonstrate that the improved model can give excellent prediction of the orientation moment distributions in a microchannel flow

Shape-Based Separation of Micro-/Nanoparticles in Liquid Phases

The production of particles with shape-specific properties is reliant upon the separation of micro-/nanoparticles of particular shapes from particle mixtures of similar volumes. However, compared to a large number of size-based particle separation methods, shape-based separation methods have not been adequately explored. We review various up-to-date approaches to shape-based separation of rigid micro-/nanoparticles in liquid phases including size exclusion chromatography, field flow fractionation, deterministic lateral displacement, inertial focusing, electrophoresis, magnetophoresis, self-assembly precipitation, and centrifugation. We discuss separation mechanisms by classifying them as either changes in surface interactions or extensions of size-based separation. The latter includes geometric restrictions and shape-dependent transport properties

A Constitutive Model for Entangled Polydisperse Linear Flexible Polymers with Entanglement Dynamics and a Configuration Dependent Friction Coefficient. Part II. Modeling Shear Modification Following Cessation of Fast Shear Flows

The polydisperse Mead-Park (MP) toy molecular constitutive model developed in Paper I [Mead et al., J. Rheol. 62, 121-134 (2017)] as well as our previously published work [e.g., J. Rheol. 59, 335-363 (2015)] is used in the forward direction to study model polydisperse melts of entangled linear flexible polymers in severe, fast shear flows. The properties of our new model are elucidated by way of numerical simulation of a representative model polydisperse polymer melt in step shear rate and interrupted shear flow. In particular, we demonstrate how the MP model simulates the individual molecular weight distribution (MWD) component dynamics as well as the bulk material properties. Additionally, we demonstrate that the polydisperse MP model predicts the phenomenon of shear modification for model MWD\u27s with a long, high molecular weight tail. Specifically, the terminal dynamic moduli following cessation of severe, disentangling deformation, are shown to slowly heal/recover on the orientational relaxation time scale of the longest chains in the MWD. This is the first molecular constitutive equation to predict the phenomenon of shear modification. We provide detailed insight into the molecular mechanism responsible for this previously enigmatic and important phenomenon. Additionally, the presence of shear modification is not necessarily associated with the presence of shear stress peak overshoot transients in interrupted shear flow. Specifically, we examine and analyze the interrupted shear experiments reported by Tsang and Dealy [J. Non-Newtonian Fluid Mech. 9, 203-222 (1981)] and demonstrate quantitatively their lack of a relationship to shear modification. We also demonstrate that the new MP model accurately predicts the Cox-Merz rule, Laun\u27s rule and Gleissele\u27s mirror relations in steady shear

Polyaniline Membranes for Nanofiltration of Solvent from Dewaxed Lube Oil

Polyaniline nanofiltration membranes were synthesized to examine a potential candidate for application of solvent recovery from lube oil. An integrally skinned polyaniline membrane was cast on a woven polyester fabric and then was chemically crosslinked with glutaraldehyde in order to further increase the membranes resistant in a methyl ethyl ketone and toluene mixture. Subsequently, membrane performance was tested under different operational conditions. The operation pressure was fixed at 35 bar and was held constant for all of the tests. The membrane demonstrated a permeate flux of 10 l/(m2 h) and oil rejection of 69%

The Shape Effect on the Retention Behaviors of Ellipsoidal Particles in Field-Flow Fractionation: Theoretical Model Derivation Considering the Steric-Entropic Mode

A theoretical model is proposed to analyze the shape effect on the retention behaviors of rod-like particles in field-flow fractionation. This model is improved from a previous model for slender-body rods by Park and Mittal [Chromatography (2015) 2: 472—487]: The model can predict the retention behaviors of the rods, of which shape is assumed as a prolate ellipsoid, with low and high aspect ratios in various flow conditions of the flow-field flow fractionation. The effects of rod aspect ratio on the retention behaviors of the rods with the same volume are investigated in each operation mode. In normal mode, the retention ratio decreases with increasing aspect ratio. In steric-entropic mode, where we substantially improved the model to evaluate the rod orientation and the cross-sectional concentration distribution more rigorously based on our recent studies [Nanomaterials (2018) 8:130; Chem. Eng. Sci. (2018) 189:396-400], the retention ratio increases with the increasing aspect ratio. In steric mode, the retention ratio decreases with increasing aspect ratio again. Those results are discussed based on how the cross-sectional concentration distributions are affected by the aspect ratio. The new criteria for the prediction of each mode are also discussed and suggested Comparison with the experimental data shows the qualitative agreement

The Effect of Weak Confinement on the Orientation of Nanorods under Shear Flows

We performed a numerical analysis to study the orientation distribution of a dilute suspension of thin, rigid, rod-like nanoparticles under shearing flow near a solid boundary of weak confinement. Brownian dynamics simulation of a rod was performed under various ratios of shear rate and rod diffusivity (Peclet number), as well as the center-of-mass position (wall confinement). We discuss the effects of Peclet number and wall confinement on the angle distributions, Jeffery orbit distribution and average orientation moments. The average orientation moments, obtained as a function of Peclet number and wall confinement, can be used to improve a previous shear-induced migration model. We demonstrate that the improved model can give excellent prediction of the orientation moment distributions in a microchannel flow

A Model for the Depletion Layer Prediction in a Dilute Suspension of Rigid Rod-Like Particles under Shear Flows in the Entire Range of Peclet Numbers

We derived a model to predict the concentration profile, or the center-of-mass distribution, of rod-like particles near a wall under shear flows. Various excluded volume mechanisms of a rod near a wall for each Peclet number (a ratio of shear rate and diffusivity) regime were incorporated into the model through a steric factor concept. At low and moderate Peclet numbers, the steric factor is mainly determined by the ratio of the restricted/unrestricted rod orientation distributions. However, at high Peclet number, the ratio between the rod penetration time in a depletion layer and the Jeffery orbit frequency mainly affects the steric factor. The predicted concentration profiles showed a good agreement with the results from previous works

Direct Numerical Simulation of Microbubble Streaming in a Microfluidic Device: The Effect of the Bubble Protrusion Depth on the Vortex Pattern

Microbubble streaming in a microfluidic device has been increasingly studied and used in recent years, due to its unique flow pattern that can promote mixing, sort particles and trap particles in microscale flows. However, there have been few numerical studies of this subject. We performed a 3D direct simulation of a cylindrical-shaped micro-bubble, trapped in a pit of a microchannel and sandwiched between two parallel plates, vibrated by pressure oscillation. Our simulation was able to reproduce the experimentally observed relation between the bubble protrusion depth and the vortex pattern: As the bubble protrusion depth increased, new vortices emerged and grew larger. Our investigation of the streamlines near the bubble interface indicates that the number of non-spherical nodes in the bubble interface is closely related to the flow pattern in the liquid phase. It was also validated by our simulation that the flow velocity showed an exponentially decaying trend as the radial distance outward from the vortex center. Our numerical model was also used to investigate the effects of surface tension and channel size on the vortex pattern. Larger surface tension or smaller channel size showed a similar effect as the increased protrusion depth induced more vortices