High Viscosity and Surface Tension

With the substantial interest in use of aqueous coating systems, an added burden is placed on the atomizing process. This burden results from the relatively high viscosities and surface tensions of aqueous systems. Fortunately, in applications using modified-release coatings, aqueous versions of such coating systems are typically in the form of latexes, or polymer dispersions, which have relatively low viscosities for the solids content of the coating system, and the presence of... 

High Viscosity and Surface Tension Bravo (Paper presented at the AIChE Spring National Meeting, Houston, Tex., 1995) studied a system that had 425-cP viscosity, 350 mN/m surface tension, and a high foaming tendency. He found that efficiencies were liquid-phase-controlled and could be estimated from theoretical HTU models. Capacity was less than predicted by conventional methods which do not account for the high viscosity. Design equations for orifice distributors extended well to the system once the orifice coefficient was calculated as a function of the low Reynolds number and the surface tension head was taken into account. 

As a major component of the natural extracellular matrix, HA has also attracted considerable attention in electrospinning. However, it is very difficult to electrospin an aqueous HA solution because its unusual high viscosity and surface tension both hinder the electrospinning process. In addition, the... 

Bandwise application of samples using spray-on technique and modem instrumental applicators, enables application of relatively large volumes of solutions (up to 99 (il). In some instances, it is even necessary to dilute solutions. The opposite situation is seen in the case of spotwise application on HPTLC plates. Recommended volumes for achieving the optimum results should not exceed 0.5 l. To obtain sufficient concentrations, samples may have to be concentrated, but concentrated aqueous solutions usually have relatively high viscosity and surface tension. This prevents the filling and emptying of capillaries caused by capillary forces. Therefore, it is advisable, if possible, to dilute concentrated solutions with methanol. Solid samples should be dissolved in distilled water (pH 5.5), dilute acid or alcohol and water mixtures, and treated as solutions. 

Properties. The physical properties of aHphatic fluorine compounds containing chlorine are similar to those of the PECs or HECs (3,5). They usually have high densities and low boiling points, viscosities, and surface tensions. The irregularity in the boiling points of the fluorinated methanes, however, does not appear in the chlorofluorocarbons. Their boiling points consistently increase with the number of chlorines present. The properties of some CECs and HCECs are shown in Tables 3 and 4. 

W-3 CHF correlation. The insight into CHF mechanism obtained from visual observations and from macroscopic analyses of the individual effect of p, G, and X revealed that the local p-G-X effects are coupled in affecting the flow pattern and thence the CHF. The system pressure determines the saturation temperature and its associated thermal properties. Coupled with local enthalpy, it provides the local subcooling for bubble condensation or the latent heat (Hfg) for bubble formation. The saturation properties (viscosity and surface tension) affect the bubble size, bubble buoyancy, and the local void fraction distribution in a flow pattern. The local enthalpy couples with mass flux at a certain pressure determines the void slip ratio and coolant mixing. They, in turn, affect the bubble-layer thickness in a low-enthalpy bubbly flow or the liquid droplet entrainment in a high-enthalpy annular flow. 

A high proportion of the complex phenomena shown by emnlsions and foams, which are common when petroleum enters the environment, can be traced to these induced surface-tension effects. Dissolved gases, even hydrocarbon gases, lower the surface tension of oils, but the effects are less dramatic and the changes probably result from dilution. The matter is of some importance in environmental issues because the viscosity and surface tension of the petroleum govern the amount of oil that migrates or can be recovered under certain conditions. 

In addition to providing highly selective separations, there are a multitude of other desired characteristics that a gas chromatographic stationary phase should possess. These properties include high viscosity, low surface tension allowing for wetting of the fused silica capillary wall, high thermal stability, and low vapor pressure at elevated temperatures. The stationary phase solvent should also not exhibit unusual mass transfer behavior. 

Joyce (29) developed the wax method of spray-particle-size measurement to a high degree of perfection during 1942 to 1946. His technique is based upon the observation that paraffin wax, when heated to a suitable temperature level above its melting point, corresponds closely, in the significant characteristics of viscosity and surface tension, with jet fuel. 

Although bubble sizes for large particles with the a-methyl styrene system have not been measured directly and any prediction must be regarded as highly speculative, Fig. 4.21 shows an estimate of the variation of mean bubble diameter with size of catalyst particles06 . This estimate is based on measurements with glass beads in water, with subsequent adjustments to allow for the different densities of the particles and differences in the viscosity and surface tension of the liquids. 

Physical interferences are generally considered to be effects associated with such properties as change in viscosity, and surface tension can cause significant inaccuracies, especially in samples that may contain high dissolved solids, or acid concentrations, or both. If these types of interferences are operative, they must be reduced by dilution of the sample or utilization of standard addition techniques, or both. 

As shown by the applications developed so far, the characteristics of acoustic levitation make it especially suitable for use in analytical and bioanalytical chemistry — however, the earliest applications focused on the determination of mechanical and physical properties of materials such as specific density, viscosity and surface tension [93,115,116]. Ohsaka et al. developed a method for determining the viscosity of highly viscous liquids (particularly, undercooled liquids, which exist at temperatures below their freezing points [117]). Weiser and Apfel used acoustic levitation to measure mechanical properties such as density, compressibility and sound velocity in biological materials [71]. 

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