Refractive fluid systems

Flow patterns of hydrodynamic systems like the compendial dissolution apparatus may be qualitatively characterized by means of dilute dye injection (e.g., methylene blue) or by techniques using particulate materials such as aluminum powders or polystyrene particles. Flow patterns may be also visualized by taking advantage of density or pH differences within the fluid stream. The Schlieren method, for instance, is based on refraction index measurement. Hot wire anemo-metry is an appropriate method to quantitatively characterize flow rates. The flow rate is proportional to the cooling rate of a thin hot wire presented to the stream. Using laser Doppler... 

For our purpose, it is convenient to classify the measurements according to the format of the data produced. Sensors provide scalar valued quantities of the bulk fluid i. e. density p(t), refractive index n(t), viscosity dielectric constant e(t) and speed of sound Vj(t). Spectrometers provide vector valued quantities of the bulk fluid. Good examples include absorption spectra A t) associated with (1) far-, mid- and near-infrared FIR, MIR, NIR, (2) ultraviolet and visible UV-VIS, (3) nuclear magnetic resonance NMR, (4) electron paramagnetic resonance EPR, (5) vibrational circular dichroism VCD and (6) electronic circular dichroism ECD. Vector valued quantities are also obtained from fluorescence I t) and the Raman effect /(t). Some spectrometers produce matrix valued quantities M(t) of the bulk fluid. Here 2D-NMR spectra, 2D-EPR and 2D-flourescence spectra are noteworthy. A schematic representation of a very general experimental configuration is shown in Figure 4.1 where r is the recycle time for the system. 

Seo et al. (1999) used a planar optic biosensor that measures the phase shift variation in refractive index due to antigen binding to antibody. In this method, they were able to detect S. enterica serovar T) himurium with a detection limit of 1 x 10 cfu/ml. When chicken carcass fluid was inoculated with 20 cfu/ml, the sensor was able to detect this pathogen after 12 h of nonselective enrichment. A compact fiber optic sensor was also used for detection of S. T) himurium at a detection limit of 1 X 10" cfu/ml (Zhou et al., 1997, 1998) however, its efficacy with food samples is unproven. Later, Kramer and Lim (2004) used the fiber optic sensor, RAPTOR , to detect this pathogen from spent irrigation water for alfalfa sprouts. They showed that the system can be used to detect Salmonella spiked at 50 cfu/g seeds. An evanescent wave-based multianalyte array biosensor (MAAB) was also employed for successful testing of chicken excreta and various food samples (sausage, cantaloupe, egg, sprout, and chicken carcass) for S. T) himurium (Taitt et ah, 2004). While some samples exhibited interference with the assay, overall, the detection limit for this system was reported to be 8 x 10 cfu/g. 

Refractive index data are very useful for the quantitation of isotropic (liquid and cubic liquid crystal) phases, and for the calibration of cell thickness and nonflatness. Hovever, the analysis of birefringent phases using refractive index data has been found to be unreliable (9). A problem arises from the fact that the orientation of such phases relative to the direction of the light path, as veil as the system variables, influence refractive indices. In order to use refractive index data for quantitation, a phase must spontaneously orient in a reproducible fashion. Such orientation does occur in the case of fluid lamellar phases (as in short chain polyoxyethylene nonionic systems (7)), but viscous lamellar phases, hexagonal phases, and crystal phases do not orient to a sufficient degree. 

There are special problems that occur when the particle diameter Is large relative to the wavelength of Incident light. This Is of Interest since many latex systems have particles with diameters of 300 to 1000 nm and a large ratio of particle to fluid refractive Index (1.2 for polystyrene latex). The most common wavelengths for lasers used In light scattering are on the order of 500 nm. 

The crudest approximation to the density matrix for the system is obtained by assuming that there are no statistical correlations between the elementary excitations (perfect fluid), so that can be written as a simple product of molecular density matrices A. A better approximation is obtained if one does a quantum field theory calculation of the local field effects in the system which in a certain approximation gives the Lorentz-Lorenz correction L(TT) in terms of the refractive index n53). One then writes,... 

In recent years one observes a growing industrial demand for organosilicon materials having properties, which can not be found in conventional polymers. These also include silicone fluids, characterized by high refraction indices, such as -1.50, utilized extensively in personal care applications. An important class of such systems are siloxanes having phenylethenyl type substituents along polymer backbone (Fig. 1). 

The R1 values obtained for such phenylethynyl substituted siloxanes are higher then that reported for traditional aromatic-based systems [9] or the phenol modified ones (1.50-1.53) [10]. The synthesis of high refractive index (methyl)(diphenyle thenyl)-dichlorosilane via hydrosilylation was also described [1]. Such monomer was later hydrolyzed and condensed into silicone fluid. Similar process was also presented, applying silylative coupling process in the synthesis of an analogous (methyl)(phenylethenyl)diethoxysilane [11], so the two reactions shall be discussed in the following section. 

The Battelle group found that photoisomerization of various indigo derivatives could be used to record holograms which had low (<0.2%) scattering efficiencies (36). Their refractive-index data yield nQ = 2.9 x 10 cm for an N,N -dibenzoylindigo derivative. These systems were reversible. The quantum yields of isomerization were much lower in poly(methyl methacrylate) or polystyrene than in fluid solution, in accord with arguments presented earlier. Concentration quenching was also observed in solution. 

To demonstrate that the gradient effect can be removed in an aligned system, similar experiments were performed by measuring a homogeneous sample of mineral oil (refractive index c 1.48), using both the ZnSe ATR accessory and the diamond ATR accessory (Supercritical Fluid Analyzer, Specac, UK). Both results... 

Although very effective for compensating the influence of the Schlieren effect, Eq. 4.7 holds only when the intensity of the Schlieren effect is not wavelength dependent, otherwise, correction factors should be added. As the transient mirrors established between fluid elements of different refractive indices are not ideal and the incident light is also partially refracted, the refraction angle is strongly wavelength dependent (Eq. 4.15). Hence, the use of Eq. 4.7 for Schlieren compensation may be subject to restrictions. Moreover, it cannot be directly applied for Schlieren compensation in flow systems with turbidimetric or nephelometric detection. 

Since dispersion of solids in a fluid-particle system is in a random state of movement, and the signals of light output from both the transmission-type and the reflection-type probes are dependent on diameter, morphology, chromaticness, distance and refractivity of the particles, the signals produced by particles in random movement can only be described by random data analysis. 

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