High frequency parallel plate probe for the measurement of the complex viscosity of liquids

In this work an instrument is described which measures the complex shear viscosity of liquids in the kHz frequency range. The instrument is driven electromagnetically and operates in resonant mode. The measurement of the primary data, from which the rheological properties of the fluid sample are inferred, does not include any deflection amplitude measuring step and is purely digital. Models allowing the interpretation of the probe primary data in terms of fluid complex viscosity are presented. The theoretically predicted mechanical behaviour of the probe is compared with the measured one and the rheometric ability of the device is discusse

High frequency parallel plate probe for the measurement of the complex viscosity of liquids

ISSN:0035-4511ISSN:1435-152

A MEMS viscometer for unadulterated human blood

The design and theoretical modelling of an oscillating micro-mechanical-viscometer designed for the measurement of whole unadulterated human blood, is described. The proposed device utilises the dependence of the squeeze-film damping ratio on properties of the surrounding fluid to measure fluid viscosity using an oscillating plate structure. The optimum geometrical configuration for the device structure has been investigated and a methodology for defining the optimum configuration of the micro-mechanical sensor identified. This is then applied to calculate the predicted noise equivalent viscosity change . It was found that the device performance is limited by electronic noise within the detection circuitry rather than thermal mechanical noise. An electronic noise limited measurement resolution of , is predicted for measurement over a shear range of , at a measurement bandwidth of . The linearity of response of the micro-mechanical-viscometer is considered and the device is predicted to provide a linear measurement response

Biopolymer-based structuring of liquid oil into soft solids and oleogels using water-continuous emulsions as templates

Physical trapping of a hydrophobic liquid oil in a matrix of water-soluble biopolymers was achieved using a facile two-step process by first formulating a surfactant-free oil-in-water emulsion stabilized by biopolymers (a protein and a polysaccharide) followed by complete removal of the water phase (by either high- or low-temperature drying of the emulsion) resulting in structured solid systems containing a high concentration of liquid oil (above 97 wt %). The microstructure of these systems was revealed by confocal and cryo-scanning electron microscopy, and the effect of biopolymer concentrations on the consistency of emulsions as well as the dried product was evaluated using a combination of small-amplitude oscillatory shear rheometry and large deformation fracture studies. The oleogel prepared by shearing the dried product showed a high gel strength as well as a certain degree of thixotropic recovery even at high temperatures. Moreover, the reversibility of the process was demonstrated by shearing the dried product in the presence of water to obtain reconstituted emulsions with rheological properties comparable to those of the fresh emulsion

L'hormone chorionique gonadotrophique et l'alpha-foetoprotéine : leur corrélation avec la pré-éclampsie

La pré-éclampsie met en jeu la vie maternelle et foetale. Aucune mesure préventive ou prédictive n'existe jusqu'à ce jour. Des études sur les marqueurs placentaires sont en cours. La βhCG et l'alpha-foetoprotéine sont des hormones dosées durant la grossesse. L'objet de cette étude est de déterminer si ces hormones sont des marqueurs précoces de la pré-éclampsie. Ce travail rétrospectif étudie un échantillon de 151 femmes. Il comprend 112 femmes appartenant au groupe témoin et 39 au groupe pré-éclampsie. Chez les patientes ayant présenté une pré-éclampsie, on note une augmentation significative de l'AFP du second trimestre. L'augmentation est plus marquée en fonction de la gravité de la pré-éclampsie. Les variations de la βhCG libre entre le groupe témoin et le groupe de pré-éclampsie ne sont pas significatives. L'AFP, associée à d'autres tests, pourrait nous aider à mettre en place une prévention primaire et secondaire de la pré-éclampsie

Structure, diffusion, and permeability of protein-stabilized monodispersed oil in water emulsions and their gels: a self-diffusion NMR study

Self-diffusion NMR is used to investigate monodispersed oil in water emulsions and the subsequent gel formed by removing the water through evaporation. The radius of the oil droplets in the emulsions is measured using a number of diffusion methods based on the measurement of the mean squared displacement of the oil, water, and tracer molecules. The results are consistent with the known size of the emulsions. Bragg-like reflections due to the restricted diffusion of the water around the oil droplets are observed due to the low polydispersity of the emulsions and the dense packing. The resulting data are fitted to a pore glass model to give the diameter of both the pools of interstitial water and the oil droplets. In the gel, information on the residual three-dimensional structure is obtained using the short time behavior of the effective diffusion coefficient to give the surface to volume ratio of the residual protein network structure. The values for the surface to volume ratio are found to be consistent with the expected increase of the surface area of monodisperse droplets forming a gel network. At long diffusion observation times, the permeability of the network structure is investigated by diffusion NMR to give a complete picture of the colloidal system considered