Viscoelasticity-induced particle migration has recently received increasing attention due to its ability to obtain high-quality focusing over a wide range of flow rates. However, its application is limited to low throughput regime since the particles can defocus as flow rate increases. Using an engineered carrier medium with constant and low viscosity and strong elasticity, the sample flow rates are improved to be one order of magnitude higher than those in existing studies. Utilizing differential focusing of particles of different sizes, here we present sheathless particle/cell separation in simple straight microchannels that possess excellent parallelizability for further throughput enhancement. The present method can be implemented over a wide range of particle/cell sizes and flow rates. We successfully separate small particles from larger particles, MCF-7 cells from red blood cells (RBCs), and Escherichia coli (E. coli) bacteria from RBCs in different straight microchannels. The proposed method could broaden the applications of viscoelastic microfluidic devices to particle/cell separation due to the enhanced sample throughput and simple channel design.Continuous manipulation and separation of particles and cells is important for a wide range of applications in biology, 1,2 medicine, 2,3 and industry. [4][5][6] Microfluidic systems have been proven to be promising tools for particle/cell manipulation with higher sensitivity and accuracy than their macroscale counterparts. The last decade has seen extensive development of microfluidic approaches for particle/cell manipulation that resort to immunocapture, 7 externally applied physical fields, [8][9][10][11][12][13][14][15][16][17][18] microfiltration, 19,20 gravitational sedimentation, 21 or deterministic lateral migration. 22,23 More recently, cross-streamline migration induced by the hydrodynamic effects of carrier media, such as inertia 24,25 and viscoelasticity, 26,27 has shown its promise for effective particle/cell manipulation without need of labeling and external force fields. Particles and cells can be separated based on the size-dependent nature of hydrodynamic forces. Briefly, the inertial lift scales as F a ∝ , where a is the particle diameter. There are several cell types of biological and clinical interest with separable size ranges: epithelial tumor cells (15-25 µm in diameter), blood cells (erythrocytes are 6-8 µm biconcave disks and peripheral blood lymphocytes are 7-10 µm in diameter), and bacteria (1-3 µm). Inertial migration in Newtonian fluids has been intensively studied and implemented in high-throughput label-free separation devices for cell separation. [28][29][30][31][32][33][34] Recently, particle migration induced by viscoelasticity has begun to attract increasing attention due to its simple focusing pattern and potential for achieving efficient focusing over a wide range of flow rates. 35,36 In a viscoelastic medium, elasticity coupled with non-negligible inertia will drive particles towards the channel centerline, whic...

Confined diffusion is ubiquitous in nature. Ever since the “anomalous yet Brownian” motion was observed, the non-Gaussianity in confined diffusion has been unveiled as an important issue. In this Letter, we experimentally investigate the characteristics and source of non-Gaussian behavior in confined diffusion of nanoparticles suspended in polymer solutions. A time-varied and size-dependent non-Gaussianity is reported based on the non-Gaussian parameter and displacement probability distribution, especially when the nanoparticle’s size is smaller than the typical polymer mesh size. This non-Gaussianity does not vanish even at the long-time Brownian stage. By inspecting the displacement autocorrelation, we observe that the nanoparticle–structure interaction, indicated by the anticorrelation, is limited in the short-time stage and makes little contribution to the non-Gaussianity in the long-time stage. The main source of the non-Gaussianity can therefore be attributed to hopping diffusion that results in an exponential probability distribution with the large displacements, which may also explain certain processes dominated by rare events in the biological environment.

We propose a fitting formula for the inertial lift on a sphere drawn from direct numerical simulation data obtained in straight microchannels. The formula consists of four terms that represent the shear-gradient-induced lift, the wall-induced lift, the slip-shear lift, and the correction of the shear-gradient-induced lift, respectively.

Viscoelastic microfluidics becomes an efficient and label-free hydrodynamic technology to enrich and separate micrometer-scale particles, including blood cells, circulating tumor cells, and bacteria. However, the manipulation of nanoscale particles by viscoelastic microfluidics remains a major challenge, because the viscoelastic force acting on the smaller particle decreases dramatically. In contrast to the commonly used polymer solutions of high molecular weight, herein we utilize the aqueous solutions of poly­(ethylene oxide) (PEO) of low molecular weight with minimized shear thinning but sufficient elastic force for high-quality focusing and separation of various nanoparticles. The focusing efficiencies of 100 nm polystyrene (PS) nanoparticles and λ-DNA molecules are 84% and 85%, respectively, in a double spiral microchannel, without the aid of sheath flows. Furthermore, we demonstrate the size-based viscoelastic separation of two sets of binary mixtures100/2000 nm PS particles and λ-DNA molecules/blood plateletsall achieving separation efficiencies of >95% in the same device. Our proposal technique would be a promising approach for enrichment/separation of the nanoparticles encountered in applications of analytical chemistry and nanotechnology.

A long-distance hop of diffusive nanoparticles (NPs) in crowded environments was commonly considered unlikely, and its characteristics remain unclear. In this work, we experimentally identify the occurrence of the intermittent hops of large NPs in crowded entangled poly­(ethylene oxide) (PEO) solutions, which are attributed to thermally induced activated hopping. We show that the diffusion of NPs in crowded solutions is considered as a superposition of the activated hopping and the reptation of the polymer solution. Such activated hopping becomes significant when either the PEO molecular weight is large enough or the NP size is relatively small. We reveal that the time-dependent non-Gaussianity of the NP diffusion is determined by the competition of the short-time relaxation of a polymer entanglement strand, the activated hopping, and the long-time reptation. We propose an exponential scaling law τhop/τe ∼ exp­(d/d t) to characterize the hopping time scale, suggesting a linear dependence of the activated hopping energy barrier on the dimensionless NP size. The activated hopping motion can only be observed between the onset time scale of the short-time relaxation of local entanglement strands and the termination time scale of the long-time relaxation. Our findings on activated hopping provide new insights into long-distance transportation of NPs in crowded biological environments, which is essential to the delivery and targeting of nanomedicines.

The microfluidic inertial effect is an effective way of focusing and sorting droplets suspended in a carrier fluid in microchannels. To understand the flow dynamics of microscale droplet migration, we conduct numerical simulations on the droplet motion and deformation in a straight microchannel. The results are compared with preliminary experiments and theoretical analysis. In contrast to most existing literature, the present simulations are three-dimensional and full length in the streamwise direction and consider the confinement effects for a rectangular cross section. To thoroughly examine the effect of the velocity distribution, the release positions of single droplets are varied in a quarter of the channel cross section based on the geometrical symmetries. The migration dynamics and equilibrium positions of the droplets are obtained for different fluid velocities and droplet sizes. Droplets with diameters larger than half of the channel height migrate to the centerline in the height direction and two equilibrium positions are observed between the centerline and the wall in the width direction. In addition to the well-known Segré-Silberberg equilibrium positions, new equilibrium positions closer to the centerline are observed. This finding is validated by preliminary experiments that are designed to introduce droplets at different initial lateral positions. Small droplets also migrate to two equilibrium positions in the quarter of the channel cross section, but the coordinates in the width direction are between the centerline and the wall. The equilibrium positions move toward the centerlines with increasing Reynolds number due to increasing deformations of the droplets. The distributions of the lift forces, angular velocities, and the deformation parameters of droplets along the two confinement direction are investigated in detail. Comparisons are made with theoretical predictions to determine the fundamentals of droplet migration in microchannels. In addition, existence of the inner equilibrium position is linked to the quartic velocity distribution in the width direction through a simple model for the slip angular velocities of droplets.

As an emerging green and sustainable solvent, a deep eutectic solvent (DES) applied to the carbon capture process is considered to be a promising absorbent. This work aims to comprehensively evaluate the potential and effectiveness of DESs for CO2 capture. First, a hydrophobic DES, which is composed of tetrabutylammonium bromide as the hydrogen bond acceptor (HBA) and decanoic acid as the hydrogen bond donor (HBD) with a molar ratio of 1:2, was screened out from 280 DESs by the conductor-like screening models–segment activity coefficient (COSMO-SAC) model. Then, quantum chemistry methods were used to investigate the interaction mechanism between the DES and CO2. The results show that the interactions between CO2 and the DES are mainly weak hydrogen bonds and van der Waals dispersion attraction forces. Next, gas–liquid equilibrium experiments were performed to investigate the effects of temperature and pressure, the types of HBAs and HBDs, and the molar ratios of HBA to HBD on the solubility of CO2. The results show that the process of DES absorbing CO2 obeys Henry’s law and confirm the reliability of the COSMO-SAC model prediction. Finally, a rigorous rate-based model for the DES-based postcombustion CO2 capture process was simulated, and the life cycle environmental sustainability was evaluated and compared with that of the traditional solvent monoethanolamine, confirming the advantages of the negligible vapor pressure, thermal stability, and low ecological toxicity of the DES. This study provides a technical reference for applying new solvents developed in the laboratory to practical industrial processes.

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