Critical angle method

Refractive index can be measured with a high precision to five decimal places using critical angle method with Bausch Lomb Precision Refractometer. This method can be used for the transparent and light colored liquids measured at temperatures from 20 to 30°C. Several light sources and filters are specified in order to provide monochromatic light. Also, calibration and calibration liquids are described to assure high precision of measnrement. 

Since the original model of Tiselius there have been many papers published that describe different methods of refractive index monitoring. From these publications, four general methods emerge for measuring refractive index the angle of deviation method, the critical angle method, the Fresnel method and the Christiansen method. The theory behind each of these methods will now be discussed. 

Critical angle method for refractive index, 395-6 Critical chain length, 176 determination, 177-9 Critical index, 127, 128 Critical point, 76 drying method, 229 Critical relaxation, 90-2 Crosslink density and relaxation time, 373 Crosslink formation, 5-7 Crosslink points, schematic diagram, 8 Crosslink points per pritnaiy polymer at gelation, 34... 

The refractive index is measured by the critical angle method with a Bausch Lomb Precision Refractometer using monochromatic light. The instrument is previously adjusted by means of a solid reference standard and the observed values are corrected, when necessary, by a calibration obtained with certified liquid standards. 

Refractometry can be used to determine the composition of a copolymer. In addition, differential refractometry has been used to study micellization in dilute block copolymer solutions (Tfizar and Kratochvfl 1972). The refractive index (n) is obtained in an Abbe refractometer via measurements of the critical angle for external reflection. The refractive index increment dn/dc, where c is the polymer concentration, can be related to the molecular weight of particles in solution. Further details of the method are provided by Pepper and Samuels (1989). 

With the applicability of this method now proved, it was worthwhile to look at the dependence of the spectra on the penetration depth. Figure 12 shows the change of the spectrum of ethanol on quartz caused by timing the angle of incidence from approx. 80 through the critical angle to a subcritical one, i.e., the laser beam is entering the optical rare material. 

Incorporation of the measured contact angle in mercury intrusion porosimetry data is essential for an accurate determination of the pore size distribution. Both the advancing and static angle methods are suitable to carry out this measurement, leading to very similar results. For most oxidic materials and supported oxides, the contact angle is 140° and incorporation of the actual contact angle is less critical in the pore size determination. However, important deviations are observed in carbon and cement-like materials, with contact angles of > 150° and < 130°, respectively. This has been shown by comparison of the pore size distribution obtained from mercury porosimetry and N2 adsorption measurements. 

The surface study was performed at BL-7C of the same facility by the total-reflection XAFS(TR-XAFS) method. The experiments were done at 1 mrad grazing incidence angle, since at the Br K-edge energy, the critical angle for the total-reflection is about 2 mrad at the water surface. In order to reduce the X-ray absorption by air and water vapor, the solution surface was covered by helium gas. 

As implied by the discussion above craze fibril extension ratio or its inverse the fibril volume fraction of the craze is an important parameter of the microstructure. Fibril volume fractions can be measured by several different methods. The refractive index n of the craze can be measured by measuring the critical angle for total reflection of light by the craze surface. Using the Lorentz-Lorenz equation Vf then can be computed from The method is difficult because small variations... 

For the sulfuric acid method of cyclization there is no angle procedure which is entirely general, because the concentration of the acid, and the reaction time and temperature, may be critical. The method of R. D. Haworth has been used in the ring closure of a large number of acids, but the description serves only to indicate the form of procedure. In order to obtain optimum yields, it may be necessary to alter the conditions and ooncentrationa... 

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