Capillary Forces 318 INDEX

Impregnation. Porous samples and delicate materials should be impregnated. This is performed with the same media which will be used to cement the sample to the slide in a later step. The impregnating medium, consisting of epoxy resin or Canada balsam, should have a suitable index of refraction (close to 1.535), allowing the phases to be distinguished from one another by optical methods. In many cases, it is sufficient to simply lay the sample in the mounting medium and then allow capillary forces to... 

It is assumed that the opening space is filled with solvent, such as alcohol. This means that the capillary force is low enough to make the shrinkage of a gel film small during the drying process, and opening spaces can remain as pores in the film after heat treatment (Sakka, 1988). Presence of these pores in a film gives rise to smaller refractive index of silica film with 2.5 r < 5 than 1.45, refractive index of dense silica. 

Currently, there are some facilities that produce rhamnolipid surfactants e.g. Rham-nolipid Inc. in United States (http //www.rhamnolipid.com/index.html) produces rhamnolipids on a relatively large scale. Their main target market is in EOR applications. A similar US-based company. Biosurfactant EOR, Inc. (http //www.bioeor.com/), also produces a range of rhamnolipids for the oil industry. The main principle in these two applications is to reduce the interfacial tension of the oil-water interface, therefore reducing the capillary forces that tend to keep the oil trapped in the reservoir. The advantage of the rhamnolipids is that they can reduce that interfacial tension to ultralow values... 

If the NMR response is capable of estimating the pore size distribution, then it also has the potential to estimate the fraction of the pore space that is capable of being occupied by the hydrocarbon and the remaining fraction that will only be occupied by water. The Free Fluid Index (FFI) is an estimate of the amount of potential hydrocarbons in the rock when saturated to a given capillary pressure. It is expressed as a fraction of the rock bulk volume. The Bulk Volume Irreducible (BVI) is the fraction of the rock bulk volume that will be occupied by water at the same capillary pressure. The fraction of the rock pore volume that will only be occupied by water is called the irreducible water saturation (Siwr = BVI/cj>). The amount of water that is irreducible is a function of the driving force to displace water, i.e., the capillary pressure. Usually the specified driving force is an air-water capillary pressure of 0.69 MPa (100 psi). 

Wettability Index (W), (based on the U.S. Bureau of Mines wettability test), in which the forced (pressure) imbibition of water is compared to forced imbibition of oil via capillary pressure curves. The wettability index varies from -oo for complete oil-wetting, to zero for neutral, to +°° for complete water-wetting. For practical purposes, W usually varies between about -1.5 and +1.0. 

As has been seen in Table 4.1, the polymer microstructure influences the application properties of the polymer, such as melt flow index (MFI). The MFI is the mass flow rate [in g (10 min) ] of a HIPS melt that flows through a capillary, when forced by a piston loaded by a constant weight. It indicates the processability of the polymer and it is an important quality control variable in the polymerization process. MFI mainly depends... 

A capillary rheometer (Fig. 6.8) is similar to a melt indexer. The main difference is that instead of by gravity, the piston is driven by a variable speed motor. Also, a load cell in-line with the piston measures ram force in real time. This configuration allows tests to be run at a controlled shear rate, and even to vary the rate over a large range during a single test run. The piston force and the orifice geometry provide the data necessary... 

The melt index is an industry standard test used to assess the processability of a polymer melt. A schematic of a melt indexer is shown in Fig. 10. It is essentially a stress-controlled capillary rheometer using a weight-driven piston to force material through a round-hole capillary die. A melt index is obtained by measuring the amount of time required for a specific volume of material to be extruded from the die, with the results presented in units of g/10 min. 

Because eq. 6.2.27 depends on both choice of constitutive equation and idealization of the deformation, it seems unwise to rely on capillary die swell data to measure normal forces. However, such data are useftil as normal stress indexes for comparing materials. 

The basic geometry of a capillary rheometer is similar to that of a melt indexer. Molten polymer in a heated barrel is extruded through a capillary die under the influence of pressure exerted by a piston. Either the force applied to the piston or its rate of travel is controllable over a wide range, as are the temperature of the polymer and the dimensions of the capillary. The relationship between the force apphed to the piston and its rate of travel reflects the response of the melt viscosity to the applied shear stress. In modem instmments, experimental control and final calculations are handled by computer. Additional refinements come in the form of interchangeable capillary dies of various lengths and diameters, the use of pressure transducers, and precisely controlled piston rates. Slit flow rheometers are also available but are far less common than capillary rheometers. The theory and practical aspects of capillary flow are extensively covered in the works cited in the bibliography. 

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