A Microtube Viscometer with a Thermostat

The viscometer presented in this paper is suit-able for measuring the viscosity of liquids in micro-litre quantities. It consists of a micro-flow experimental system with a thermostat. Using the measurements of the flow rates and pressure drops of a liquid passing through a microtube, the liquid's viscosity can be calculated from on Hagen-Poiseuille theory. After calibration, the viscometer was used to measure viscosities of deionized water and ethyl alcohol at temperatures ranging from 0 to 40 "C. For both test liquids, the relative deviation of the measured values from those quoted in the literature (obtained using other viscometers) was less than 2.6o/o. The relative uncertainty of the experimental system was reduced to +-l.8% using the relative measuring method. Due to the micro-scale of the test section, only a micro-litre quantity of liquid is needed for a test, this is a potential advantage for measurement of bio-liquid viscosities.

A polytetrafluoroethylene capillary viscometer

A polytetrafluoroethylene(PTFE) capillary Ubbelohde viscometer was designed and constructed. The relative viscosities of aqueous solutions of a polyethylene oxide and a polyvinylpyrrolidone sample were carefully determined down to an extremely dilute concentration region. In comparison with the data obtained from the common glass capillary viscometer, slippage is believed to occur in the PTFE capillary due to its hydrophobic nature. While for the glass capillary viscometer, conventional viscous flow is operative and adsorption phenomena occur since both the solvent water and aqueous solution are wet and/or adsorbed onto the glass capillary surface due to the existence of hydroxyl groups on glass surface. The data were analyzed with a recently developed wall-effect theory and satisfactory results were obtained.

Stepping-motor-driven constant-shear-rate rotating viscometer

Despite the frequent use of stepping motors in robotics, automation, and a variety of precision instruments, they can hardly be found in rotational viscometers. This paper proposes the use of a stepping motor to drive a conventional constant-shear-rate laboratory rotational viscometer to avoid the use of velocity sensor and gearbox and, thus, simplify the instrument design. To investigate this driving technique, a commercial rotating viscometer has been adapted to be driven by a bipolar stepping motor, which is controlled via a personal computer. Special circuitry has been added to microstep the stepping motor at selectable step sizes and to condition the torque signal. Tests have been carried out using the prototype to produce flow curves for two standard Newtonian fluids (920 and 12 560 mPa (.) s, both at 25 degrees C). The flow curves have been obtained by employing several distinct microstep sizes within the shear rate range of 50-500 s(-1). The results indicate the feasibility of the proposed driving technique.

A Constant Torque Micro-Viscometer

We present a technique to measure the viscosity of microscopic volumes of liquid using rotating optical tweezers. The technique can be used when only microlitre (or less) sample volumes are available, for example biological or medical samples, or to make local measurements in complicated micro-structures such as cells. The rotation of the optical tweezers is achieved using the polarisation of the trapping light to rotate a trapped birefringent spherical crystal, called vaterite. Transfer of angular momentum from a circularly polarised beam to the particle causes the rotation. The transmitted light can then be analysed to determine the applied torque to the particle and its rotation rate. The applied torque is determined from the change in the circular polarisation of the beam caused by the vaterite and the rotation rate is used to find the viscous drag on the rotating spherical particle. The viscosity of the surrounding liquid can then be determined. Using this technique we measured the viscosity of liquids at room temperature, which agree well with tabulated values. We also study the local heating effects due to absorption of the trapping laser beam. We report heating of 50-70 K/W in the region of liquid surrounding the particle.

Studies on transport phenomena during solidification of an aluminum alloy in the presence of linear electromagnetic stirring

Numerical and experimental studies on transport phenomena during solidification of an aluminum alloy in the presence of linear electromagnetic stirring are performed. The alloy is electromagnetically stirred to produce semisolid slurry in a cylindrical graphite mould placed in the annulus of a linear electromagnetic stirrer. The mould is cooled at the bottom, such that solidification progresses from the bottom to the top of the cylindrical mould. A numerical model is developed for simulating the transport phenomena associated with the solidification process using a set of single-phase governing equations of mass. momentum, energy. and species conservation. The viscosity variation of the slurry, used in the model, is determined experimentally using a rotary viscometer. The set of governing equations is solved using a pressure-based finite volume technique, along with an enthalpy based phase change algorithm. The numerical study involves prediction of temperature, velocity, species and solid fraction distribution in the mould. Corresponding solidification experiments are performed, with time-temperature history recorded at key locations. The microstructures at various temperature measurement locations in the solidified billet are analyzed. The numerical predictions of temperature variations are in good agreement with experiments, and the predicted flow field evolution correlates well with the microstructures observed at various locations.

Dynamic viscosity of ternary mixtures of dichlorodifluoromethane (R-12), chlorodifluoromethane (R-22), and dichlorotetrafluoroethane (R-114) vapors

The viscosities of ternary mixtures of R-12, R-22, and R-114 vapors were determined at ambient temperature and pressure within +-1% by using an oscillating disk viscometer. The empirical viscosity obtained by Wllke's equation compares very well with the experimental results obtained with this vlscometer. In the case of this ternary vapor mixture, as long as the molar fraction ratio of R-12 to R-114 Is maintained at approximately 2"' (=Inverse ratio of thelr molecular weights) the viscosity of the ternary mixture at ambient temperature and pressure remalns constant irrespective of the percentage of R-22 present in the mixture.

Dynamic viscosity of gas mixtures

The viscosity of five binary gas mixtures - namely, oxygen-hydrogen, oxygen-nitrogen, oxygen-carbon dioxide, carbon dioxide-nitrogen, carbon dioxide-hydrogen - and two ternary mixtures - oxygen-nitrogen-carbon dioxide and oxygen-hydrogen-carbon dioxide - were determined at ambient temperature and pressure using an oscillating disk viscometer. The theoretical expressions of several investigators were in good agreement with the experimental results obtained with this viscometer. In the case of the ternary gas mixture oxygen-carbon dioxide-nitrogen, as long as the volumetric ratio of oxygen to carbon dioxide in the mixture was maintained at 11 to 8, the viscosity of the ternary mixture at ambient temperature and pressure remained constant irrespective of the percentage of nitrogen present in the mixture.

Evolution of Microstructure During Solidification of an Aluminium Alloy Under Stirring

In the present work, the evolution of microstructure during solidification of A356 alloy under stirring is performed experimentally in a high temperature concentric viscometer. The stirring during solidification results a semisolid slurry in the annular space between the cylinders. This slurry is removed periodically during processing using a vacuum removal quartz tube and quenched in water for micrograph analysis. From the micrograph analysis, the shape, stacking arrangement and corresponding microstructural evolution of the suspended primary particles in the slurry are studied. The work also predicts the fraction of solid present in the extracted slurry. Finally, the effect of microstructure and the solid-fraction on the slurry viscosity is presented.

Rheology of A356 Alloy During Solidification Under Stirring

This work presents an experimental investigation on the rheology of A356 alloy in semisolid state using a high temperature Couette type viscometer. The molten liquid, resides in the annular space between the cylinders, is stirred and cooled continuously during experiments. The stirring results in fragmentation of dendrites which are transported into bulk liquid and form a semisolid slurry. The viscosity of the slurry is distinct in nature, which depends on microstructure of the suspended dendrites after coarsening. Hence, in the work, the variation of viscosity and microstructure is captured during cooling under different process parameters such as shear rate and cooling rate. Angular velocity of the inner cylinder and torque applied to stir the slurry are recorded to determine the apparent viscosity of the slurry. Temperature of the slurry is recorded to calculate the fraction of solids present in the slurry. For micrograph analysis, a vacuum quartz tube is used to remove the slurry-samples during experiments and they are quenched them in water.

Two-Dimensional Kinetics Of Beta(2)-Integrin And Icam-1 Bindings Between Neutrophils And Melanoma Cells In A Shear Flow

Cell adhesion, mediated by specific receptor-ligand interactions, plays an important role in biological processes such as tumor metastasis and inflammatory cascade. For example, interactions between beta(2)-integrin ( lymphocyte function-associated antigen-1 and/or Mac-1) on polymorphonuclear neutrophils (PMNs) and ICAM-1 on melanoma cells initiate the bindings of melanoma cells to PMNs within the tumor microenvironment in blood flow, which in turn activate PMN-melanoma cell aggregation in a near-wall region of the vascular endothelium, therefore enhancing subsequent extravasation of melanoma cells in the microcirculations. Kinetics of integrin-ligand bindings in a shear flow is the determinant of such a process, which has not been well understood. In the present study, interactions of PMNs with WM9 melanoma cells were investigated to quantify the kinetics of beta(2)-integrin and ICAM-1 bindings using a cone-plate viscometer that generates a linear shear flow combined with a two-color flow cytometry technique. Aggregation fractions exhibited a transition phase where it first increased before 60 s and then decreased with shear durations. Melanoma-PMN aggregation was also found to be inversely correlated with the shear rate. A previously developed probabilistic model was modified to predict the time dependence of aggregation fractions at different shear rates and medium viscosities. Kinetic parameters of beta(2)-integrin and ICAM-1 bindings were obtained by individual or global fittings, which were comparable to respectively published values. These findings provide new quantitative understanding of the biophysical basis of leukocyte-tumor cell interactions mediated by specific receptor-ligand interactions under shear flow conditions.

Microfluidic Rheometry

The development and growth of microfluidics has stimulated interest in the behaviour of complex liquids in micro-scale geometries and provided a rich platform for rheometric investigations of non-Newtonian phenomena at small scales. Microfluidic techniques present the rheologist with new opportunities for material property measurement and this review discusses the use of microfluidic devices to measure bulk rheology in both shear and extensional flows. Capillary, stagnation and contraction flows are presented in this context and developments, limitations and future perspectives are examined. (C) 2008 Elsevier Ltd. All rights reserved.

The shape parameter of Liposomes and DNA-lipid complexes determined by viscometry utilizing small sample volumes

A minicapillary viscometer utilizing <0.5 ml of sample at a volume fraction of <0.1% is described. The calculated a/b of DPPC/DPPG multilamellar liposome was 1.14 as prolate ellipsoids and a/b of dioleoylpropyltrimethyl ammonium methylsulfate-DNA complex at a charge ratio of 4: 1 (+/-) was 3.7 as prolate ellipsoids or 4.9 as oblate ellipsoids. The deviation of shape from perfect sphere is thus expressed quantitatively in more than two significant figures. In these measurement, the necessary amount of DNA is <0.5 mg.

Analysis of interfacial phenomena of aqueous solutions of polyethylene oxide and polyethylene glycol flowing in hydrophilic and hydrophobic capillary viscometers

Viscosities of aqueous solutions of five polyethylene oxide (PEO) samples with molar masses from 1.5 x 10(5) to 1.0 x 10(6) were carefully measured in a polytetrafluoroethylene (PTFE) capillary Ubbelohde viscometer in the concentration range from dilute down to extremely dilute concentration regions and compared with those of the same sample obtained from a glass capillary viscometer. At the same time, viscosities of aqueous solutions of three PEG samples in glass and paraffin-coated capillary viscosity were measured. The wall effects occurred in viscosity measurements for PEO and PEG aqueous solutions in different capillary viscometers were theoretically analyzed and discussed. It was found that different interfacial behaviors occurred in both hydrophobic and hydrophilic capillary viscometers respectively and the interfacial behaviors also exhibit molar mass dependence.

Rheological properties and crystallization behavior of yttrium oxide filled low ethylene content polypropylene copolymer

The rheological properties and crystallization characteristics of low ethylene content poly propylene (EPM) with and without Yittrium oxide (Y2O3) as a filler was investigated by cone-plate viscometer and differential scanning calorimetry. Yittrium oxide had a profound effect on the viscosities of the systems. To determine the nonisothermal crystallization rate of the materials, a new estimation method was used. From the results, we can conclude that Y2O3 acts as a nucleating agent, which increased the crystallization rate of the EPM. (C) 1996 John Wiley & Sons, Inc.

Biosensors using photonic crystal fibres

In this thesis, we present the unique properties of hollow-core photonic crystal fibres (HC-PCFs) for sensing applications in terms of viscosity detection and DNA sensing using a special poly(ethylene) glycol (PEGDA) hydrogel. The low loss HC-PCFs ensure a long interaction length between the sample and the optical signals. Thus in this thesis, we report the characterisation of filled HC-PCFs and the development of a selective filling process. For the first time, we report the investigation of a new viscometer device, and a new device for DNA sensing development, and also the chemical process for hydrogel growth was adapted to the fibres. By combining HC-PCFs with the hydrogel we enable 3D volumetric sample confinement within the HC-PCF, further increasing the interaction between the sample and the optical signal. However, the hydrogel has a large influence on the guidance properties of the HC-PCF and the HC-PCF has a strong influence on the growth process for the hydrogel itself. When we integrate the hydrogel and HC-PCFs we detect concentration levels as low as 400 nM of labelled DNA. However, using our technology for fluorescence detection we can achieve results two orders of magnitude better than those previously reported.