Ching-Chang Chieng

Fluid filling into micro-fabricated reservoirs

Abstract This study reports that the success of reservoir-filling strongly depends on the designs of the hydrophilic wall surface and the well shape/size of the flow network. The idea is illustrated both by experiments and numerical simulations: micro-particle-image-velocimetry (μ-PIV) system is setup to monitor the process of a liquid slug moving in and out of the micro-reservoir and numerical computations are performed by solving first principle equations to provide the details of the flow process. The cross-check between measurements and computations validate the computations. Numerical computations solve conservation equations similar to homogenous flow model used in two phase flow calculation in co-operation with volume-of-fluid (VOF) interface tracking methodology and continuum surface force (CSF) model. The simulations show that wall surface property as hydrophilic/hydrophobic is a dominating factor in filling processes of reservoirs of various shapes. A flow system consisting of micro-channels and micro-wells is fabricated using MEMS technology to demonstrate the filling process and validate numerical simulation. The agreement between measurement and computation helps to fully understand the process.

Effective enhancement of fluorescence detection efficiency in protein microarray assays: application of a highly fluorinated organosilane as the blocking agent on the background surface by a facile vapor-phase deposition process.

Protein microarrays are emerging as an important enabling technology for the simultaneous investigation of complicated interactions among thousands of proteins. The solution-based blocking protocols commonly used in protein microarray assays often cause cross-contamination among probes and diminution of protein binding efficiency because of the spreading of blocking solution and the obstruction formed by the blocking molecules. In this paper, an alternative blocking process for protein microarray assays is proposed to obtain better performance by employing a vapor-phase deposition method to form self-assembled surface coatings using a highly fluorinated organosilane as the blocking agent on the background surfaces. Compared to conventional solution-based blocking processes, our experimental results showed that this vapor-phase process could shorten the blocking time from hours to less than 10 min, enhance the binding efficiency by up to 6 times, reduce the background noise by up to 16 times, and improve the S/N ratio by up to 64 times. This facile blocking process is compatible with current microarray assays using silica-based substrates and can be performed on many types of silane-modified surfaces.

Uniform Solute Deposition of Evaporable Droplet in Nanoliter Wells

There have been many microdeposition processes that are based on the evaporation of nanoliter-sized droplets, such as inkjet printing, deoxyribonucleic acid/protein microarrays, or lithography direct writing. However, it is important but still difficult to control the uniformity of the solute deposition from a nanoliter sessile droplet on a plane substrate. This paper proposes a method for uniform solute deposition from evaporable droplet by confining the droplet with rib structures (wells) of specific surface properties. The hydrodynamic process was experimentally investigated and analyzed in detail. Surface wettability on the well surface is verified to be critical for controlling a droplet as a flat film inside a well during evaporation to minimize horizontal solute transfer for uniform solute deposition. Pure water and water/tracing particle mixture (2.57% solid latex, dyed blue) were employed for the test. The results demonstrated that a 97% uniformity is obtained for the solute deposited from a 37-nL droplet in a well with hydrophobic surface (contact angle of 100deg), whereas a 31% uniformity is obtained for a more hydrophilic surface (contact angle of 25deg). The higher hydrophobicity (contact angle above 90deg) on the well surface yields a flatter profile of film during droplet evaporation inside a well and, thus, promotes a more uniform deposition of the solute.

Roles of nanolayer and particle size on thermophysical characteristics of ethylene glycol-based copper nanofluids

Calculation of thermal conductivity and the characterization of the molecular-level mechanisms of ethylene-glycol-based copper nanofluid are conducted using the molecular dynamics (MD) Simulation when the nanoparticle size ranges from 6 to 14 A. Layer–Maxwell model is developed for the calculation of effective thermal conductivity of the nanofluid with nanoparticle size up to 2000 A by the application of distinct thermal conductivity in the nanolayers around nanoparticle obtained from MD simulations. The comparison between computational and experimental results reveals the roles of interfacial layer and nanoparticle size in the thermal conductivity enhancement.

Molecular dynamics simulation of the enhancement of cobra cardiotoxin and E6 protein binding on mixed self-assembled monolayer molecules

Molecular dynamics simulations are performed on n-alkinethiol self-assembled monolayers (SAMs) and their mixture on a gold surface so that the orientations of the binding of cobra cardiotoxin and E6 protein molecules can be selected using the mixing ratio of CH3-terminated SAMs with different chain lengths. The simulations suggest that a SAM surface with different mixing ratios may provide a possible platform for aligning protein molecules with a desired orientation and for enhancing the binding energy of the protein on the designed surface.

Enhanced thermal conductivity of nanofluids diagnosis by molecular dynamics simulations.

Boehmite nanoparticles covered with a polymer shell enhancing the organophilicity of the surface were prepared by physical adsorption of a polyelectrolyte atom transfer radical polymerization (ATRP) macroinitiator followed by graft-polymerization of methyl methacrylate or 2-hydroxyethyl methacrylate. The presence of polymer chains adsorbed/grafted on the Boehmite was confirmed by attenuated total reflection infrared (ATR-IR) spectroscopy and by thermo-gravimetric analysis (TGA), which showed a significant amount of polymer covering the particles. The methodology of polymerization and the kinetics suggested the possibility to modulate the amount, type and thickness of grafted polymer shell. These organic-inorganic hybrid materials were melt compounded in a Brabender mixer with isotactic polypropylene in the presence of functionalized polypropylene. The dispersion degree of Boehmite nanoparticles in the polypropylene matrix as well as their reinforcing effect were studied by morphology characterization [scanning electron microscopy (SEM) and X-ray diffraction (XRD)], whereas thermal and thermo-mechanical properties were assessed by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA).

Protein micro arrays immobilized by μ-stamps and -protein wells on PhastGel® pad

This paper reports a novel stamping system, employing μ-stamps and -protein wells to simultaneously transfer proteins onto an array without de-naturalization, cross-contamination, and de-attachment of the proteins. The μ-stamps and -protein wells were successfully fabricated by micro machining and micro molding process. The effect of surface properties of μ-stamp on micro printing has been studied, and results demonstrated the feasibility of printing protein arrays with spot-size of 350 m square and pitch of 100 m. Testing results show that each stamped protein sample can be clearly identified with uniform deposition, and lasts for 6 h under water washing without appreciable de-attachment. This method may be used to transfer numerous different protein samples with the help of pre-filled μ-protein wells.

NUMERICAL SIMULATIONS OF ELECTRO-SLAG REMELTING PROCESS

Flow and heat transfer characteristics in the electro-slag remelting process (ESR) are important in manufacturing steel of good quality. An integrated numerical model is developed to compute the flow field and the temperature distribution inside ESR units with a metal pool profile which is solved simultaneously. In addition to the conservative equations of mass, momentum, energy, and turbulent properties, Maxwells equations are employed to obtain the electromagnetic field by either AC or DC power supply. The results include the effects of power supply type, current amplitude, casting rate, and flow field patterns (laminar or turbulent) on flow and heat transfer characteristics. Different flow patterns and turbulent properties have been predicted using a pool profile close to the real one for AC and DC power supplies. The present model concludes that the casting rate and current amplitude are very effective in affecting the pool shape.

EULERIAN-LAGRANGIAN COMPUTATIONS ON PHASE DISTRIBUTION OF TWO-PHASE BUBBLY FLOWS

SUMMARY A comprehensively theoretical model is developed and numerically solved to investigate the phase distribution phenomena in a two-dimensional, axisymmetric, developing, two-phase bubbly flow. The Eulerian approach treats the fluid phase as a continuum and solved Eulerian conservation equations for the liquid phase. The Lagrangian bubbles are tracked by solving the equation of motion for the gas phase. The interphase momentum changes are included in the equations. The numerical model successfully predicts detailed flow velocity profiles for both liquid and gas phases. The development of the wall-peaking phenomenon of the void fraction and velocity profiles is also characterized for the developing flow. For 42 experiments in which the mean void fraction is less than 20 per cent, numerical calculations demonstrate that the predictions agree well with Liu’s experimental data. 1997 by John Wiley & Sons, Ltd.

Constructing a force interaction model for thermal conductivity computation using molecular dynamics simulation: Ethylene glycol as an example

This study aims to construct a force interaction model for thermal conductivity computation and to analyze the liquid properties in atomic level for liquid ethylene glycol (EG) using molecular dynamic simulation. The microscopic details of the molecular system and the macroscopic properties of experimental interest are connected by Green-Kubo relations. In addition, the major contributions of heat transfer modes for thermal conductivity due to convection, interaction, and torque are obtained quantitatively. This study reveals that the intramolecular interaction force fields result in different conformations of the EG in the liquid and thus the molecular shapes. The trans∕gauche ratio for EGs O-Me-Me-O torsional angle and the number of intermolecular∕intramolecular H-bonds are found to be important parameters affecting the thermal conductivity.