Frequency-Dependent Viscosity of Membrane Solutions

It is shown that dilute suspensions of membranes have strongly frequency-dependent viscosities. This behaviour should be seen in a variety of measurements such as capillary flow, mechanical impedance and ultrasound damping.

Functional Surfaces for Microfluidics in Proteomic Analysis

Microchips for use in biomolecular analysis show a lot of promise for medical diagnostics and biomedical basic research. Among the potential advantages are more sensitive and faster analyses as well as reduced cost and sample consumption. Due to scaling laws, the surface are to volume ratios of microfluidic chips is very high. Because of this, tailoring the surface properties and surface functionalization are very important technical issues for microchip development. This thesis studies two different types of functional surfaces, surfaces for open surface capillary microfluidics and surfaces for surface assisted laser desorption ionization mass spectrometry, and combinations thereof. Open surface capillary microfluidics can be used to transport and control liquid samples on easily accessible open surfaces simply based on surface forces, without any connections to pumps or electrical power sources. Capillary filling of open partially wetting grooves is shown to be possible with certain geometries, aspect ratios and contact angles, and a theoretical model is developed to identify complete channel filling domains, as well as partial filling domains. On the other hand, partially wetting surfaces with triangular microstructures can be used for achieving directional wetting, where the water droplets do not spread isotropically, but instead only spread to a predetermined sector. Furthermore, by patterning completely wetting and superhydrophobic areas on the same surface, complex droplet shapes are achieved, as the water stretches to make contact with the wetting surface, but does not enter into the superhydrophobic domains. Surfaces for surface assisted laser desorption ionization mass spectrometry are developed by applying various active thin film coatings on multiple substrates, in order to separate surface and bulk effects. Clear differences are observed between both surface and substrate layers. The best performance surfaces consisted of amorphous silicon coating and an inorganic-organic hybrid substrate, with nanopillars and nanopores. These surfaces are used for matrix-free ionization of drugs, peptides and proteins, and for some analytes, the detection limits were in the high attomoles. Microfluidics and laser desorption ionization surfaces are combined on a functionalized drying platforms, where the surface is used to control the shape of the deposited analyte droplet, and the shape of the initial analyte droplet affects the dried droplet solute deposition pattern. The deposited droplets can then directly detected by mass spectrometry. Utilizing this approach, results of analyte concentration, splitting and separation are demonstrated.

Micropillar Array Based Microchips for Electrospray Ionization Mass Spectrometry, Microreactors, and Liquid Chromatographic Separation

This dissertation deals with the design, fabrication, and applications of microscale electrospray ionization chips for mass spectrometry. The microchip consists of microchannel, which leads to a sharp electrospray tip. Microchannel contain micropillars that facilitate a powerful capillary action in the channels. The capillary action delivers the liquid sample to the electrospray tip, which sprays the liquid sample to gas phase ions that can be analyzed with mass spectrometry. The microchip uses a high voltage, which can be utilized as a valve between the microchip and mass spectrometry. The microchips can be used in various applications, such as for analyses of drugs, proteins, peptides, or metabolites. The microchip works without pumps for liquid transfer, is usable for rapid analyses, and is sensitive. The characteristics of performance of the single microchips are studied and a rotating multitip version of the microchips are designed and fabricated. It is possible to use the microchip also as a microreactor and reaction products can be detected online with mass spectrometry. This property can be utilized for protein identification for example. Proteins can be digested enzymatically on-chip and reaction products, which are in this case peptides, can be detected with mass spectrometry. Because reactions occur faster in a microscale due to shorter diffusion lengths, the amount of protein can be very low, which is a benefit of the method. The microchip is well suited to surface activated reactions because of a high surface-to-volume ratio due to a dense micropillar array. For example, titanium dioxide nanolayer on the micropillar array combined with UV radiation produces photocatalytic reactions which can be used for mimicking drug metabolism biotransformation reactions. Rapid mimicking with the microchip eases the detection of possibly toxic compounds in preclinical research and therefore could speed up the research of new drugs. A micropillar array chip can also be utilized in the fabrication of liquid chromatographic columns. Precisely ordered micropillar arrays offer a very homogenous column, where separation of compounds has been demonstrated by using both laser induced fluorescence and mass spectrometry. Because of small dimensions on the microchip, the integrated microchip based liquid chromatography electrospray microchip is especially well suited to low sample concentrations. Overall, this work demonstrates that the designed and fabricated silicon/glass three dimensionally sharp electrospray tip is unique and facilitates stable ion spray for mass spectrometry.

Hantavirus glycoprotein GN in virion assembly and regulation of interferon response

Hantaviruses have a tri-segmented negative-stranded RNA genome. The S segment encodes the nucleocapsid protein (N), M segment two glycoproteins, Gn and Gc, and the L segment the RNA polymerase. Gn and Gc are co-translationally cleaved from a precursor and targeted to the cis-Golgi compartment. The Gn glycoprotein consists of an external domain, a transmembrane domain and a C-terminal cytoplasmic domain. In addition, the S segment of some hantaviruses, including Tula and Puumala virus, have an open reading frame (ORF) encoding a nonstructural potein NSs that can function as a weak interferon antagonist. The mechanisms of hantavirus-induced pathogenesis are not fully understood but it is known that both hemorrhagic fever with renal syndrome (HFRS) and hantavirus (cardio) pulmonary syndrome (HCPS) share various features such as increased capillary permeability, thrombocytopenia and upregulation of TNF-. Several hantaviruses have been reported to induce programmed cell death (apoptosis), such as TULV-infected Vero E6 cells which is known to be defective in interferon signaling. Recently reports describing properties of the hantavirus Gn cytoplasmic tail (Gn-CT) have appeared. The Gn-CT of hantaviruses contains animmunoreceptor tyrosine-based activation motif (ITAM) which directs receptor signaling in immune and endothelial cells; and contain highly conserved classical zinc finger domains which may have a role in the interaction with N protein. More functions of Gn protein have been discovered, but much still remains unknown. Our aim was to study the functions of Gn protein from several aspects: synthesis, degradation and interaction with N protein. Gn protein was reported to inhibit interferon induction and amplication. For this reason, we also carried out projects studying the mechanisms of IFN induction and evasion by hantavirus. We first showed degradation and aggresome formation of the Gn-CT of the apathogenic TULV. It was reported earlier that the degradation of Gn-CT is related to the pathogenicity of hantavirus. We found that the Gn-CT of the apathogenic hantaviruses (TULV, Prospect Hill virus) was degraded through the ubiquitin-proteasome pathway, and TULV Gn-CT formed aggresomes upon treatment with proteasomal inhibitor. Thus the results suggest that degradation and aggregation of the Gn-CT may be a general property of most hantaviruses, unrelated to pathogenicity. Second, we investigated the interaction of TULV N protein and the TULV Gn-CT. The Gn protein is located on the Golgi membrane and its interaction with N protein has been thought to determine the cargo of the hantaviral ribonucleoprotein which is an important step in virus assembly, but direct evidence has not been reported. We found that TULV Gn-CT fused with GST tag expressed in bacteria can pull-down the N protein expressed in mammalian cells; a mutagenesis assay was carried out, in which we found that the zinc finger motif in Gn-CT and RNA-binding motif in N protein are indispensable for the interaction. For the study of mechanisms of IFN induction and evasion by Old World hantavirus, we found that Old World hantaviruses do not produce detectable amounts of dsRNA in infected cells and the 5 -termini of their genomic RNAs are monophosphorylated. DsRNA and tri-phosphorylated RNA are considered to be critical activators of innate immnity response by interacting with PRRs (pattern recognition receptors). We examined systematically the 5´-termini of hantavirus genomic RNAs and the dsRNA production by different species of hantaviruses. We found that no detectable dsRNA was produced in cells infected by the two groups of the old world hantaviruses: Seoul, Dobrava, Saaremaa, Puumala and Tula. We also found that the genomic RNAs of these Old World hantaviruses carry 5´-monophosphate and are unable to trigger interferon induction. The antiviral response is mainly mediated by alpha/beta interferon. Recently the glycoproteins of the pathogenic hantaviruses Sin Nombre and New York-1 viruses were reported to regulate cellular interferon. We found that Gn-CT can inhibit the induction of IFN activation through Toll-like receptor (TLR) and retinoic acid-inducible gene I-like RNA helicases (RLH) pathway and that the inhibition target lies at the level of TANK-binding kinase 1 (TBK-1)/ IKK epislon complex and myeloid differentiation primary response gene (88) (MyD88) / interferon regulatory factor 7 (IRF-7) complex.

Modified-Pore-Filled-PVDF-Membrane Electrolytes for Direct Methanol Fuel Cells

The polyvinylidene fluoride (PVDF) membrane is modified by the chemical etchant-route employing a sodium naphthalene charge-transfer complex followed by impregnation with Nafion ionomer or polyvinyl alcohol (PVA)-polystyrene sulfonic acid (PSSA) polymeric blend solutions by a dip-coating technique to form pore-filled-membrane electrolytes for application in direct methanol fuel cells (DMFCs). The number of coatings on the surface-modified PVDF membrane is varied between 5 and 15 and is found to be optimum at 10 layers both for Nafion and PVA-PSSA impregnations for effective DMFC performance. Hydrophilicity of the modified-membrane electrolytes is studied by determining average contact angle and surface-wetting energy. Morphology of the membranes is analyzed by a cross-sectional scanning electron microscope. The modified PVDF membrane electrolytes are characterized for their water-methanol sorption in conjunction with their mechanical properties, proton conductivity, and DMFC performance. Air permeability for the modified membranes is studied by a capillary-flow porometer. Methanol crossover flux across modified-PVDF-membrane electrolytes is studied by measuring the mass balance of methanol using a density meter. DMFCs employing membrane electrode assemblies with the modified PVDF membranes exhibit a peak power-density of 83 mW/cm(2) with Nafion impregnation and 59 mW/cm(2) for PVA-PSSA impregnation, respectively. Among the membranes studied here, stabilities of modified-pore-filled PVDF-Nafion and PVDF-PVA-PSSA membranes with 10-layers coat are promising for application in DMFCs. (C) 2010 The Electrochemical Society. DOI: 10.1149/1.3518774] All rights reserved.

Dimple and nose coalescences in phase-separation processes

Coalescence processes are investigated during phase separation in a density-matched liquid mixture (partially deuterated cyclohexane and methanol) under near-critical conditions. As a result of the interplay between capillary and lubrication forces, ''nose'' coalescence appears to be always associated with the slow growth of isolated droplets (exponent almost-equal-to 1/3), whereas ''dimple'' coalescence corresponds to the fast growth of interconnected droplets (exponent almost-equal-to 1). At each stage of growth, the distribution of droplets trapped during dimple coalescence is reminiscent of all of the previous coalescence events.

Collapse Behavior of an Artificially Cemented Clayey Silt

The present study examines the role of interparticle cementation in the collapse behavior of two partly saturated (S-r = 4 to 12%) and very highly porous (initial void ratio = 1.5 to 2) laboratory-desiccated clayey silt specimens containing varying amounts (5 and 15% by dry weight of the respective specimens) of the cementitious iron oxides hematite and goethite, which are generally encountered in tropical residual soils. Kaolinite is the representative clay mineral of the soil matrix used for this research. Interparticle cementation by the crystalline iron oxides was generated in the laboratory by repeated (six times) wetting and drying of the iron-hydroxide-admixed clayey silt specimens under ambient conditions of temperature and humidity. Results showed that, for a given laboratory-desiccated clayey silt specimen (i.e., a specimen containing 5 or 15% of iron oxide on a dry weight basis), the amount of collapse (represented by Delta epsilon, the change in vertical strain upon wetting under constant pressure) increases with an increase in the experimental loading under which the specimen is inundated. The laboratory results also show that the desiccated specimen with a higher iron oxide content (containing 15% iron oxide by dry weight of the desiccated specimen) in spite of a lower dry unit weight (gamma(d) = 8.8 kN/m(3)) undergoes a lesser amount of collapse on soaking under a constant external stress (50 or 100 kPa) than the desiccated specimen with a lower iron oxide content (i.e., containing 5% iron oxide by dry weight of the desiccated specimen, gamma(d) = 10.4 KN/m(3)). Based on the X-ray diffraction results and the stress-strain relationships obtained from isotropically consolidated undrained triaxial tests, it is suggested that the laboratory-desiccated specimens are characterized by a metastable bonding provided by capillary suction and the crystalline iron oxides. On soaking under load owing to the loss of the metastable bonding, collapse of the laboratory-desiccated specimens occurs. Also, in the case of the laboratory-desiccated specimen with a higher iron oxide content, the presence of a stronger interparticle cementation (due to a greater abundance of crystalline iron oxides) and a higher initial moisture content are considered responsible for the specimen exhibiting a lower amount of collapse in comparison to that exhibited by the desiccated specimen with a lesser iron oxide content.

Stability of the viscous flow of a fluid through a flexible tube

The stability of Hagen-Poiseuille flow of a Newtonian fluid of viscosity eta in a tube of radius R surrounded by a viscoelastic medium of elasticity G and viscosity eta(s) occupying the annulus R < r < HR is determined using a linear stability analysis. The inertia of the fluid and the medium are neglected, and the mass and momentum conservation equations for the fluid and wall are linear. The only coupling between the mean flow and fluctuations enters via an additional term in the boundary condition for the tangential velocity at the interface, due to the discontinuity in the strain rate in the mean flow at the surface. This additional term is responsible for destabilizing the surface when the mean velocity increases beyond a transition value, and the physical mechanism driving the instability is the transfer of energy from the mean flow to the fluctuations due to the work done by the mean flow at the interface. The transition velocity Gamma(t) for the presence of surface instabilities depends on the wavenumber k and three dimensionless parameters: the ratio of the solid and fluid viscosities eta(r) = (eta(s)/eta), the capillary number Lambda = (T/GR) and the ratio of radii H, where T is the surface tension of the interface. For eta(r) = 0 and Lambda = 0, the transition velocity Gamma(t) diverges in the limits k much less than 1 and k much greater than 1, and has a minimum for finite k. The qualitative behaviour of the transition velocity is the same for Lambda > 0 and eta(r) = 0, though there is an increase in Gamma(t) in the limit k much greater than 1. When the viscosity of the surface is non-zero (eta(r) > 0), however, there is a qualitative change in the Gamma(t) vs. k curves. For eta(r) < 1, the transition velocity Gamma(t) is finite only when k is greater than a minimum value k(min), while perturbations with wavenumber k < k(min) are stable even for Gamma--> infinity. For eta(r) > 1, Gamma(t) is finite only for k(min) < k < k(max), while perturbations with wavenumber k < k(min) or k > k(max) are stable in the limit Gamma--> infinity. As H decreases or eta(r) increases, the difference k(max)- k(min) decreases. At minimum value H = H-min, which is a function of eta(r), the difference k(max)-k(min) = 0, and for H < H-min, perturbations of all wavenumbers are stable even in the limit Gamma--> infinity. The calculations indicate that H-min shows a strong divergence proportional to exp (0.0832 eta(r)(2)) for eta(r) much greater than 1.

Transient analysis of mammalian cell growth in hollow fibre bioreactor

A mathematical model describing the dynamics of mammalian cell growth in hollow fibre bioreactor operated in closed shell mode is developed. Mammalian cells are assumed to grow as an expanding biofilm in the extra-capillary space surrounding the fibre. Diffusion is assumed to be the dominant process in the radial direction while axial convection dominates in the lumen of the bioreactor. The transient simulation results show that steep gradients in the cell number are possible under the condition of substrate limitation. The precise conditions which result in nonuniform growth of cells along the length of the bioreactor are delineated. The effect of various operating conditions, such as substrate feed rate, length of the bioreactor and diffusivity of substrate in different regions of the bioreactor, on the bioreactor performance are evaluated in terms of time required to attain the steady-state. The rime of growth is introduced as a measure of effectiveness factor for the bioreactor and is found to be dependent on two parameters, a modified Peclet number and a Thiele modulus. Diffusion, reaction and/or convection control regimes are identified based on these two parameters. The model is further extended to include dual substrate growth limitations, and the relative growth limiting characteristics of two substrates are evaluated. (C) 1997 Elsevier Science Ltd.

A numerical model of a liquid-feed solid polymer electrolyte DMFC and its experimental validation

A one-dimensional, biphasic, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymeric electrolyte membrane has been developed for a liquid-feed solid polymer electrolyte direct methanol fuel cell (SPE- DMFC). The model employs three important requisites: (i) implementation of analytical treatment of nonlinear terms to obtain a faster numerical solution as also to render the iterative scheme easier to converge, (ii) an appropriate description of two-phase transport phenomena in the diffusive region of the cell to account for flooding and water condensation/evaporation effects, and (iii) treatment of polarization effects due to methanol crossover. An improved numerical solution has been achieved by coupling analytical integration of kinetics and transport equations in the reaction layer, which explicitly include the effect of concentration and pressure gradient on cell polarization within the bulk catalyst layer. In particular, the integrated kinetic treatment explicitly accounts for the nonhomogeneous porous structure of the catalyst layer and the diffusion of reactants within and between the pores in the cathode. At the anode, the analytical integration of electrode kinetics has been obtained within the assumption of macrohomogeneous electrode porous structure, because methanol transport in a liquid-feed SPE- DMFC is essentially a single-phase process because of the high miscibility of methanol with water and its higher concentration in relation to gaseous reactants. A simple empirical model accounts for the effect of capillary forces on liquid-phase saturation in the diffusion layer. Consequently, diffusive and convective flow equations, comprising Nernst-Plank relation for solutes, Darcy law for liquid water, and Stefan-Maxwell equation for gaseous species, have been modified to include the capillary flow contribution to transport. To understand fully the role of model parameters in simulating the performance of the DMCF, we have carried out its parametric study. An experimental validation of model has also been carried out. (C) 2003 The Electrochemical Society.

Crystal structure of quenched and in-field electroluminescent phosphors

Electroluminescent zinc sulfide doped with copper and chloride (ZnS:Cu, Cl) powder was heated to 400°C and rapidly quenched to room temperature. Comparison between the quenched and non-quenched phosphors using synchrotron radiation X-ray powder diffraction (XRPD) (λ = 0.828692 Å) and X-ray absorption spectroscopy (XAS) was made. XRPD shows that the expected highly faulted structure is observed with excellent resolution out to 150° 2θ (or to (12 2 2) of the sphalerite phase). The quenched sample compared to the unheated sample shows a large change in peak ratios between 46.7° and 46.9°, which is thought to correspond to the wurtzite (0 0 6), (0 3 2) and sphalerite (3 3 3)/(5 1 1) peaks. Hence, a large proportion of this sphalerite diffraction is lost from the material upon rapid quenching, but not when the material is allowed to cool slowly. The Zn K-edge XAS data indicate that the crystalline structures are indistinguishable using this technique, but do give an indication that the electronic structure has altered due to changing intensity of the white line. It is noted that the blue electroluminescence (EL) emission bands are lost upon quenching: however, a large amount of total EL emission intensity is also removed, which is consistent with our findings. We report the XRPD of a working alternating-current electroluminescence device in the synchrotron X-ray beam, which exhibits a new diffraction pattern when the device is powered in an AC field even though the phosphor is fixed in the binder. Significantly, only a few crystals are required to yield the diffraction data because of the high flux X-ray source. These in panel data show multiple sharp diffraction lines spread out under the region, where capillary data show broad diffraction intensity indicating that the phosphor powder is comprised of unique crystals, each having different structures.

Instabilities of soft elastic microtubes filled with viscous fluids: Pearls, wrinkles, and sausage strings

A linear stability analysis is presented to study the self-organized instabilities of a highly compliant elastic cylindrical shell filled with a viscous liquid and submerged in another viscous medium. The prototype closely mimics many components of micro-or nanofluidic devices and biological processes such as the budding of a string of pearls inside cells and sausage-string formation of blood vessels. The cylindrical shell is considered to be a soft linear elastic solid with small storage modulus. When the destabilizing capillary force derived from the cross-sectional curvature overcomes the stabilizing elastic and in-plane capillary forces, the microtube can spontaneously self-organize into one of several possible configurations; namely, pearling, in which the viscous fluid in the core of the elastic shell breaks up into droplets; sausage strings, in which the outer interface of the mircrotube deforms more than the inner interface; and wrinkles, in which both interfaces of the thin-walled mircrotube deform in phase with small amplitudes. This study identifies the conditions for the existence of these modes and demonstrates that the ratios of the interfacial tensions at the interfaces, the viscosities, and the thickness of the microtube play crucial roles in the mode selection and the relative amplitudes of deformations at the two interfaces. The analysis also shows asymptotically that an elastic fiber submerged in a viscous liquid is unstable for Y = gamma/(G(e)R) > 6 and an elastic microchannel filled with a viscous liquid should rupture to form spherical cavities (pearling) for Y > 2, where gamma, G(e), and R are the surface tension, elastic shear modulus, and radius, respectively, of the fiber or microchannel.

Synthesis, structural characterization and ferroelectric properties of Pb(0.76)Ca(0.24)TiO(3) nanotubes

A capillary-enforced template-based method has been applied to fabricate Pb(0.76)Ca(0.24)TiO(3) (PCT24) nanotubes via filling PCT24 precursor solution, prepared by modified sol-gel method, into nanochannels of anodic aluminum oxide templates. The morphology and structure of as-prepared PCT24 were examined by scanning electron microscopy, transmission electron microscopy (TEM) and X-ray diffraction techniques. The obtained PCT24 nanotubes with diameter of similar to 200 nm and wall thickness of similar to 20 nm exhibited a tetragonal perovskite structure. High resolution TEM (HRTEM) analysis confirmed that as-obtained PCT24 nanotubes made up of nanoparticles (5-8 nm) which were randomly aligned in the nanotubes. Formation of some solid crystalline PCT24 nanorods, Y-junctions and multi-branches were observed. Interconnections in the pores of template are responsible for the growth of Y-junctions and multi-branches. The possible formation mechanism of PCT24 nanotubes/nanorods was discussed. Ferroelectric hysteresis loops of PCT24 nanotube arrays were measured, showing a room temperature ferroelectric characteristic of as-prepared PCT24 nanotubes. (C) 2011 Elsevier B.V. All rights reserved.

Influence of ethanol/water mixture on the undrained shear strength of pure clays

The mechanical properties of clays are highly dependent not only on the stress/strain ratio to which the material is subjected but also on the chemistry of the pore fluids which in turn affects the intergranular or the effective stresses. Atterberg limits and vane shear tests were performed with different pore fluids in order to observe how the fine-grained material mechanically responded. The diffuse double layer theory has been used to interpret the data of vane shear tests in order to explain the variation of geotechnical responses with the different clays. Van der Waals forces and double layer forces were obtained and capillary forces calculated. The results show that while for kaolinite and illite the chemistry of the pore fluids has no influence on the water content and hence on the mechanical behaviour of the material, Na-smectite shows a strong correlation between the dielectric constant of the pore fluids and an increase in undrained shear strength. The data obtained extends an understanding of the influence of the dielectric constant (epsilon) of the pore fluids on the geotechnical properties of fine-grained materials.

Spreading and atomization of droplets on a vibrating surface in a standing pressure field

We report the first observation and analytical model of deformation and spreading of droplets on a vibrating surface under the influence of an ultrasonic standing pressure field. The standing wave allows the droplet to spread, and the spreading rate varies inversely with viscosity. In low viscosity droplets, the synergistic effect of radial acoustic force and the transducer surface acceleration also leads to capillary waves. These unstable capillary modes grow to cause ultimate disintegration into daughter droplets. We find that using nanosuspensions, spreading and disintegration can be prevented by suppressing the development of capillary modes and subsequent break-up. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4757567]