Publications by authors named "Kyung Hyun Ahn"

Heterogeneous photocatalysis offers substantial potential for sustainable energy conversion, yet its industrial application is constrained by limited durability under stringent photochemical conditions. Achieving high photocatalytic activity often requires harsh reaction conditions, compromising catalyst stability and longevity. Here we propose a strategy involving polymeric stabilization of photocatalytic centres uniquely localized at the gas-liquid interface, substantially enhancing both the catalytic activity and stability.

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  • The size and shape of graphite are crucial for the performance of lithium-ion batteries and affect the manufacturing of electrode slurries.
  • A novel method was developed to accurately characterize graphite particles' edge size and shape by aligning them through a specific flow field in a microchannel.
  • The study reveals that ball-milled graphite has a different shape compared to natural graphite, which impacts the rheological properties of slurries, electrode structures, and ultimately the electrochemical performance of the batteries.
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 The greater the viscosity of the blood, the more difficult its flow becomes, leading to an increased incidence of diseases caused by blood circulation disorders. These diseases are commonly associated with the cardiovascular and cerebrovascular systems. High blood viscosity is a primary cause of circulatory system diseases.

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Processing of electrode slurry, which is highly non-Newtonian fluid, is a critical step in the mass production of lithium-ion batteries (LIBs). While extensional flow plays an important role in the electrode slurry processes such as coating, most previous studies have focused only on the shear rheology, due to the lack of a reliable method to measure the extensional rheological properties of the slurry. Here, it is demonstrated that the extensional rheological properties of the anode slurries can be successfully characterized using the stop-flow-dripping-onto-substrate/capillary break-up rheometry (SF-DoS/CaBER).

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  • The study investigates how blood viscosity affects stroke outcomes and its clinical usefulness when measured at hospital arrival.
  • Among 112 patients suspected of having a stroke, blood viscosity was significantly higher in those with ischemic stroke compared to those diagnosed with stroke mimics.
  • The findings suggest that measuring blood viscosity can help differentiate ischemic stroke from other conditions, as it correlates with different shear rates at various frequencies.
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  • The text discusses the potential of using microbial metabolism to convert sunlight and organic carbon into sustainable energy, highlighting the current limitations in developing effective microbial platforms for fuel production.
  • A new microbial device inspired by water lily leaves is introduced, which functions at the air-water interface, enhancing the supply and capture of gases while optimizing sunlight delivery.
  • The device, utilizing the microorganism Rhodopseudomonas parapalustris, demonstrates significantly improved hydrogen production rates compared to traditional devices, showcasing its promise for efficient and sustainable solar energy conversion.
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Storing solar energy in chemical bonds aided by heterogeneous photocatalysis is desirable for sustainable energy conversion. Despite recent progress in designing highly active photocatalysts, inefficient solar energy and mass transfer, the instability of catalysts and reverse reactions impede their practical large-scale applications. Here we tackle these challenges by designing a floatable photocatalytic platform constructed from porous elastomer-hydrogel nanocomposites.

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Clogging is ubiquitous. It happens in a wide range of material processing and causes severe performance degradation or process breakdown. In this study, we investigate clogging dynamics in a single micropore by controlling the surface property of the particle and processing condition.

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The evolution of the normal stress and microstructure in the drying process of bidisperse colloidal films is studied using the Brownian dynamics simulation. Here, we show that the formation process of small-on-top stratification can be explained by normal stress development. At high 's, a stratified layer with small particles is formed near the interface.

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A ternary composite of poly(lactic acid) (PLA), poly(caprolactone) (PCL), and carbon black (CB) shows the PCL-induced CB self-aggregation and percolation formation when the amount of the PCL phase as the secondary phase is as small as the amount of CB. Furthermore, when the drop size of the PCL phase becomes smaller, the ternary composite forms a percolation of high order structure, resulting in a remarkable enhancement of the electrical conductivity (~4 × 10 S/m with 4 wt.% CB).

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We carry out a numerical study to investigate the dynamics of non-Brownian hard-sphere suspensions near the liquid and crystal coexistence region in small to large amplitude oscillatory shear flow. The first normal stress difference (N1) and related rheological functions are carefully analyzed, focusing on the strain stiffening phenomenon, which occurs in the large strain amplitude region. Under oscillatory shear, we observe several unique behaviors of N1.

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A binder plays a critical role in dispersion of coating liquids and the quality of coating. Poly(vinylidene fluoride) (PVDF) is widely used as a binder in cathode slurries; however, its role as a binder is still under debate. In this paper, we study the role of PVDF on the rheology of cathode battery slurries consisting of Li(NiMnCo)O (NCM), carbon black (CB) and N-methyl-2-pyrrolidone (NMP).

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We suggest a numerical method to describe particle dynamics at the fluid interface. We adopt a coupling strategy by combining the color gradient lattice Boltzmann method (CGLBM) and smoothed profile method (SPM). The proposed scheme correctly resolves the momentum transfer among the solid particles and fluid phases while effectively controlling the wetting condition.

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Air pollution is one of the most serious problems facing mankind because of its impact on ecosystems and human beings. Although particulate matter (PM) consists of both filterable PM (FPM) and condensable PM (CPM), most research has focused on eliminating only FPM. In this work, we introduce a filter system that removes both FPM and CPM from pollution source with high efficiency.

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  • This study focuses on optimizing a microfluidic crossflow filtration system by integrating a staggered herringbone micromixer (SHM).
  • Computational fluid dynamics (CFD) and the Taguchi method were used to identify optimal design parameters that reduce fouling, investigating how flow and mass transfer differ between the SHM model and a plain rectangular microchannel.
  • Key design parameters evaluated include the number of grooves, groove depth, inter-groove spacing, and half mixing period spacing, with Analysis of Variance (ANOVA) helping to pinpoint their contributions, ultimately demonstrating that the optimized SHM model minimizes wall concentration growth the most effectively.
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We explore the relaxation behavior of model colloidal gels under steady shear flow by means of orthogonal superposition rheometry. Fumed silica and carbon black dispersions in Newtonian matrices are used as a model system. As shear rate increases, the frequency dependent orthogonal moduli of the gels shift along the frequency axis without changing their shape, which finally can be superimposed to yield a single master curve.

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Deformation and breakup of a single agglomerate exposed to pure planar extensional flow in a cross-channel were experimentally investigated. Aggregation was generated by applying shear with destabilized polystyrene particles, and the fractal dimension, d, of the agglomerate was 2.25.

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A systematic study has been performed to investigate the effect of surface potential of nanoparticles on the rheological behavior of bimodal suspensions, using a model system consisting of polystyrene latex (primary size ∼530 nm) and alumina-coated silica (primary size ∼12 nm) particles. The surface potential of small particles was tuned by varying the solution pH, causing them to be repulsive to each other, attractive to each other, and oppositely charged to the large particles, while the large particles remained electrostatically stabilized. We found that the rheological properties could be dramatically changed from viscous to gel-like depending on the surface potential and concentration of small particles.

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The dynamics and rheological behavior of colloidal gels under oscillatory shear flow have been studied by using the Brownian dynamics simulations. The dynamics is studied under the oscillatory shear of small, medium, and large amplitudes. In the small amplitude oscillatory shear (SAOS) regime, the colloidal gel retains a rigid-chain network structure.

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Preheating of dental composites improves their flowability, facilitating successful restorations. However, the flowability of dental composites is affected not only by temperature but also by the deformation conditions. In the present work, the effects of various deformation conditions upon the viscoelastic properties of a preheated dental composite were studied.

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Coculturing stem cells with the desired cell type is an effective method to promote the differentiation of stem cells. The features of the membrane used for coculturing are crucial to achieving the best outcome. Not only should the membrane act as a physical barrier that prevents the mixing of the cocultured cell populations, but it should also allow effective interactions between the cells.

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We report a type of colloidal gel, induced by a minute incremental addition of mutually attractive small particles (size ∼12 nm) to a suspension of highly charged large particles (size ∼500 nm). The gel's morphological behavior does not follow the typical power-law scaling for fractal clusters. Its unique scaling behavior has two distinct power-law indices, based on particle volume fraction.

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Concentrated hard-sphere suspensions in the liquid and crystal coexistence region show a unique nonlinear behavior under a large amplitude oscillatory shear flow, the so-called strain stiffening, in which the viscosity or modulus suddenly starts to increase near a critical strain amplitude. Even though this phenomenon has been widely reported in experiments, its key mechanism has never been investigated in a systematic way. To have a good understanding of this behavior, a numerical simulation was performed using the lattice Boltzmann method (LBM).

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The local shear stress of non-Brownian suspensions was investigated using the lattice Boltzmann method coupled with the smoothed profile method. Previous studies have only focused on the bulk rheology of complex fluids because the local rheology of complex fluids was not accessible due to technical limitations. In this study, the local shear stress of two-dimensional solid particle suspensions in Couette flow was investigated with the method of planes to correlate non-Newtonian fluid behavior with the structural evolution of concentrated particle suspensions.

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We study the mechanism of depletion stabilization and the resultant microstructure of aqueous suspensions of nanosized silica and poly(vinyl alcohol) (PVA). Rheology, small-angle light scattering (SALS), and small-angle X-ray scattering (SAXS) techniques enable us to analyze the microstructure at broad length scale from single particle size to the size of a cluster of aggregated particles. As PVA concentration increases, the microstructure evolves from bridging flocculation, steric stabilization, depletion flocculation to depletion stabilization.

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