Opaque samples

Commercially available photon tunneling microscopes have a lateral resolution of 160 nm but subnanometer vertical resolution. The nondestmctive, instantaneous 3-D viewing of a surface (no scanning) yields real-time imaging as one traverses a given sample. The sample must be a dielectric, but transparent polymer tepHcas of opaque samples can be studied. 

As an example of a more speeifie applieation, Figure 2 illustrates a metallo-graph—a light microscope set up for the characterization of opaque samples. Figure 3 illustrates a research-grade microscope made specifically for materials science, i.e., for optically characterizing all transparent and translucent materials. 

A variety of commercial instruments are available for PL measurements. These include spectrofluorometers intended primarily for use with liquids in a standard configuration, and simple filter-based systems for monitoring PL at a single wavelength. For use with opaque samples and surfaces, a few complete commercial systems are available or may be appropriately modified with special attachments, but due to the wide range of possible configuration requirements it is common to assemble a custom system from commercial optical components. 

Isoperibolic calorimetry measurements on the n-butanol/water and n-butoxyethanol/water systems have demonstrated the accuracy and convenience of this technique for measuring consolute phase compositions in amphiphile/water systems. Additional advantages of calorimetry over conventional phase diagram methods are that (1) calorimetry yields other useful thermodynamic parameters, such as excess enthalpies (2) calorimetry can be used for dark and opaque samples and (3) calorimetry does not depend on the bulk separation of conjugate fluids. Together, the present study and studies in the literature encompass all of the classes of compounds of the amphiphile/CO ydrocarbon/water systems that are encountered in... 

For IR sensing, three transducer principles are standard classical transmission for (sufficiently) transparent samples, (diffuse) reflection for opaque samples, in particular solids and strongly turbid liquids and attenuated total reflection (ATR), in particular for strongly absorbing samples and fluids with varying amounts of suspended solids or gas bubbles. 

P.O.36 is also used to color unsaturated polyester resins. Both transparent and opaque samples exhibit a lightfastness in these media that equals step 7 on the Blue Scale. The pigment does not affect the shrinkage of the plastic. 

The increase of pore size with increasing amount of solvent can also be monitored with dynamic DSC-measurements. An endothermic peak at T=7 °C, corresponding to the melting point of crystalline cyclohexane, is observed in the opaque samples after the phase separation resulting from the formation of dispersed cyclohexane droplets (Fig. 53). 

The density drop between the transparent sample with initially 15 wt % cyclohexane, and the opaque sample with 16 wt % cyclohexane, is around 17%. We... 

In fluorescence, the sample under analysis behaves like a light source, emitting in all directions. The emitted light is usually monitored perpendicular to the primary excitation source. For strongly absorbing solutions, measurements can be made on-axis with the incident radiation. For opaque or semi-opaque samples, a frontal... 

As illustrated by the examples discussed here, the use of FT spectrometers for the observation of surface structures is favored by situations in which the flux of radiation coming from the sample is very low or the data acquisition time is limited. Such cases arise in transmission spectroscopy using strongly absorbing or scattering samples, specular and diffuse reflectance spectroscopy from opaque samples, and emission spectroscopy from low temperature sources. FT spectroscopy is also well suited for observing the dynamics of surface species during adsorption, desorption, and reaction. 

Wilkinson F, Willsher CJ, Warwick P, Land EJ, Rushton FAP (1984) Diffuse reflectance pulse radiolysis of opaque samples. Nature 311 40-42... 

Often single crystals suitable for absorption spectroscopy cannot be grown, but the problem can be overcome by the use of excitation spectroscopy. With narrow band tuneable lasers highly resolved spectra of polycrystalline and opaque samples can be obtained. 

Figure 16.36. Experimental layout to perform analyses of laser-induced fluorescence (LIF) spectroscopy of opaque samples.

Attenuated total reflection FTIR is a well-established technique for obtaining absorbance spectra of opaque samples. The mode of interaction is unique because the probing radiation is propagated in a high index-of-refraction internal reflection element (IRE). The radiation interacts with the material of interest, which is in close contact with the IRE, forming an interface across which a nonpropagating evanescent field penetrates the surface of the material of interest to a depth in the order of one wavelength of the radiation. The electric field at the interface penetrates the rarer medium in the form of an evanescent field whose amplitude decays exponentially with distance into the rarer medium. 

The recording of infrared spectra of solid and opaque samples, such as silica, has not always been trivial. An often used technique consisted of pressing approximately 2 -5% of the sample with KBr into a self-supporting disk at 10 tons. 

The introduction of Fourier Transform Infrared Spectroscopy (FTIR) brought along a number of typical solid sample techniques. DRIFTS (Diffuse Reflectance Fourier Transform Infrared Spectroscopy) is probably most commonly known. Another technique, developed specifically for measuring solid, opaque samples is PAS (Photo Acoustic Spectroscopy). This accessory is less known, probably due to its high cost and its rather difficult modus operandi. 

Rapid Scan Opaque Samples Micro Sampling Spectral Subtraction... 

If the scatter is assumed to occur from two sources, the colorant(s) and the substrate, it is considered two-constant theory. An example of this theory is the formulation of opaque samples where titanium dioxide is blended with other pigments to achieve color. In this case the titanium dioxide becomes the second source of scatter. 

Sample Characteristics. In many Kubelka-Munk color-matching systems the user is required to present an opaque sample to the spectrophotometer. Depending on the application, this can be done a number of ways. For coatings, the technique of cross-coating several layers of colorant until opacity is achieved is commonly used. The generated sample then has become inconsistent with the typical process thickness. Although this can add error to the formulation, it will still adhere to the limitations of the Kubelka-Munk equation [7],... 

The degree of translucency can be measured by calculating a contrast ratio. This number is the ratio of the L value in color measurement obtained when backing the natural sample with a black tile divided by the L value of the sample backed with a white tile. A completely opaque sample will have a contrast ratio of 1.00. Contrast ratio measurements are specific to the thickness of the sample and the intensity of the light source. Contrast ratios for several resins are presented in Table... 

Delocalisation onto oxygen stabilizes radicals considerably. An important example is the ascorbate radical (Scheme 1.3) formed by electron-loss from the ascorbate anion, or electron-capture by dehydroascorbate. This is remarkably stable, and is characterized by an ESR doublet (1.7 G) which is quite distinctive. Because of the high sensitivity of ESR spectroscopy, and the fact that opaque samples can be used, ascorbate radical intermediates have been widely studied (Liu et al., 1988a). The most probable structure is shown in Scheme 1.3 but this is still a matter of some controversy (Liu et al., 1988a). A key factor in the formation of ascorbate radicals is that ascorbate anions... 

Fig. 3.9. Method used to study the diffuse reflectance of opaque samples in pulse radiolysis (Adams et al., 1991). The insert shows the method used to mount the sample. The electrons pass through the thin aluminium plate and the probe light through the quartz window. The scattered beam is analysed in the normal way with a monochromator, care being taken to exclude normal reflected light.

A completely transparent sample would have T= 1 or A = 0, while a completely opaque sample would have T = 0 or A =. ... 

In order to observe backward scattered CARS signals from the surface of an opaque sample a special CARS set-up has been made, which is essentially the standard configuration as displayed in Fig. 3.6-8 with specific modifications. The latter is shown in detail in Fig. 3.6-9. Here, the sample area from Fig. 3.6-8 is reproduced together with the modification. In this case, the Stokes beam runs parallel above the pump beam. Both... 

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