This paper presents a novel method in viscosity assessment using a tracking of the ball moving in Newtonian fluid. The movement of the ball is assimilated to a free fall within a tube containing liquid of whose we want to measure a viscosity. In classical measurement, height of fall is estimated directly by footage where accuracy is not really considered. Falling ball viscometers have shown, on the one hand, a limit in the ball falling height measuring, on the other hand, a limit in the accuracy estimation of velocity and therefore a weak precision on the viscosity calculation of the fluids. Our technique consist to measure the fall height by taking video sequences of the ball during its fall and thus estimate its terminal velocity which is an important parameter for cinematic velocity computing, using the Stokes formalism. The time of fall is estimated by cumulating time laps between successive video sequences which mean that we can finally estimate the cinematic viscosity of the studied fluid.
Traditional methods such as rotational viscometer and other viscometer methods are limited in their ability to investigate rheological properties of high viscous liquids. This study introduces a new approach to overcome these obstacles. Deep eutectic solvents suffer from high viscosity and they are relatively expensive. Therefore, there is a requirement to both reduce the volumes of samples required and increase the accuracy of the technique at high viscosities. Quartz crystal microbalance techniques have been applied because they provide quick recording, the potential for collecting a large amount of data in a short time. Furthermore, the quartz crystal microbalance microviscometer has the advantage over most other methods of viscometry not in its precision of absolute viscosity measurement but in the very small amount of sample liquid needed for investigation. To test the precision of quartz crystal microbalance a comparison must be made between readings obtained with a rotational viscometer set up alongside. In this investigation a series of deep eutectic solvents with various viscosities and physical characteristics have been tested. The influence of the addition of water to the liquids was also assessed.
Temperature dependence of the shear viscosity measured for isotropic liquids belonging to the three homologous series: 4-(trans-4'-n-alkylcyclohexyl) isothiocyanatobenzenes (C_n H_{2n+1} CyHx Ph NCS; nCHBT, n=0÷12), n-alkylcyanobiphenyls (C_nH_{2n+1} Ph Ph CN; nCB, n=2÷12) and 1,n-alkanediols (HO(CH_2)_nOH; 1,nAD, n=2÷10) were analysed with the use of Arrhenius equation and its two modifications: Vogel-Fulcher and proposed in this paper. The extrapolation of the isothermal viscosity of 1,n-alkanediols (n=2÷10) to n=1 leads to an interesting conclusion concerning the expected viscosity of methanediol, HOCH_2OH, the compound strongly unstable in a pure state.
The aim of this work was to study rheological behavior of nanofluids affected by electric field and temperature. We used transformer oil-based magnetic fluids, the suspensions of permanently magnetized colloidal particles (Fe_3O_4) coated by a stabilizing surfactant and immersed in transformer oil. The rheological characterization of transformer oil-based magnetic fluid was performed using the rotational rheometer MCR 502 in the shear rate from 10 to 1000 s¯¹.The strength of electric field was changed in the interval 0-6 kV cm¯¹. The flow curves and viscosity functions detected at three different temperatures 25, 50, and 75°C disclose rheological characteristics of samples, first of all the viscosity growth under increasing strength of electric field.
The paper presents results of the shear viscosity measurements performed on diluted binary mixtures of mesogenic solvent n-hexylcyanobiphenyl (C_6H_{13}PhPhC≡N,6CB) and two non-mesogenic admixtures: (i) n-heptylcyanophenyl (C_7H_{15}PhC≡N,7CP), composed of the molecules of the same polarity as the solvent molecules but of a slightly shorter length, and (ii) 4-n-propylcyclohexyl-4'-n-pentylphenyl (C_3H_7CyHxPhC_5H_{11},3CyP5), composed of the non-polar molecules but of a length very close to that of the mesomorphic solvent molecules. The experiment showed that the concentrational depression of the clearing temperature and the temperature extent of the isotropic + nematic (I + N) two-phase region in the mixtures are significantly smaller, i.e. the nematic phase is more thermodynamically stable, when the admixture molecular length is compatible to that of the mesogenic solvent, regardless of the polarity of the admixture molecules. The activation energy for freely flowing mixtures in the isotropic, nematic, and two-phase I + N regions was determined and discussed.
In this work we have studied the effect of temperature on the viscosity of magnetic fluids (MFs) based on the transformer oil ITO 100. The volume concentration of suspended magnetic particles (MPs) changed from 0.25 to 1%. Rheological characterization of MFs was performed using a vibroviscometer at working frequency of 30 Hz. The temperature dependence of the viscosity was measured in the temperature range from 20 up to 50 °C. The magnetization of different concentrations of MPs in MFs was determined by using the vibrating sample magnetometer.
Biological properties of synthetic polymers can be improved by surface modification with the use of liquid oxidizers. A resorbable biomedical polymer - poly(glycolide-co-ε-caprolactone) (PGCL) was incubated in 0.1 M NaOH for 2, 6, 16, and 24 h, followed by excessive washing and drying in vacuum. Surface properties of the materials before and after modification were evaluated: wettability by contact angle measurements, topography by atomic force microscopy, and chemical functions by infrared spectroscopy. Applied modification improved wettability of PGCL due to creation of chemical oxygenated functionalities, and resulted in a slight alternation of the surface topography and roughness. In order to determine whether NaOH incubation caused structural changes in bulk of PGCL, positron annihilation lifetime spectroscopy, differential scanning calorimetry and viscosity measurements were performed. It was found that the ortho-positronium lifetime in PGCL declines as a function of modification time. It suggests that NaOH incubation causes structural changes in PGCL not only on the surface but also in bulk.
Changes of the poly(L-lactide-co-glycolide) structure as a function of degradation time in phosphate-buffered saline for 7 weeks were investigated by gel permeation chromatography, differential scanning calorimetry, nuclear magnetic resonance (^1H NMR), and positron annihilation lifetime spectroscopy. Surface properties as wettability by sessile drop and topography by atomic force microscopy were also characterized. Chain-scission of polyester bonds in hydrolysis reaction causes a quite uniform decrease in molecular weight, and finally results in an increase in semicrystallinity. Molecular composition of the copolymer and water contact angle do not change considerably during degradation time. Atomic force microscopy studies suggest that the copolymer degrades by "in bulk" mechanism. The average size of the molecular-level free volume holes declines considerably after one week of degradation and remains constant till the sixth week of degradation. The free volume fraction decreases as a function of degradation time.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.