Diffuse spots

In order to utilize TLC on preparative scale, microgram amounts of an analyte are separated from milligram quantities of another analyte from their mixtures. The results are summarized in Table 14.1 and Table 14.2. At higher loading of an analyte, separation possibilities are reduced owing to the formation of diffused spots. 

Mortimer86 has also recommended the two-dimensional method, using ethyl acetate-acetic acid-water and ethyl acetate-formamide-pyridine as developers. Methyl Cellosolve-ethyl methyl ketone-ammonium hydroxide may also be used. Since high content of water and the presence of an alcohol in the solvent mixture gave rise to diffuse spots, formamide was substituted for water. RF values relative to the movement of orthophosphate were determined and found to vary with the distance the solvent moved. Also, in complex mixtures, the presence of some esters resulted in elongation of other ester spots. This effect and the RF variation observed-do not conform to the concept of a liquid-liquid distribution process. 

Figure 26-22 Comeal foreign body removal with subsequent healing. (A) Small metallic comeal foreign body arrow) is noted in superior cornea. (BJ After removal with a spud, a small crater-like depression remains that stains with NaFl arrow). (C) The following day, the epithelium is virtually healed, but a small focal area of edema and leukocyte infiltration remains arrow). (D) Five days later, the epithelium has healed completely, and a small diffuse spot of edema is noted arrow), which ultimately resolved.

CNS Copper deposits affect the whole CNS. Degeneration and tissue loss as well as atrophy of the lenticular nucleus prevail. Occasionally, there are also small necrotic foci with a diffuse spot-like distribution. Micro-cavernous lesions occur due to the destruction of nerve cells. Myelinized fibres and oligodendrocytes are present, but there is also cellular hyperplasia and hypertrophy of astrocytes rich in protoplasm. The cerebral changes detectable in CT scanning do not correlate with the degree of severity of the functional disturbances (320, 335) however, there is a close correlation between the lesions detected by MRI and certain neurological findings. (350, 366, 376, 388) (s. p. 615)... 

Thermal diffuse scattering Diffuse scattering results from a departure from a regular periodic character of a crystal lattice. It is evident as diffuse spots or blurs around normal diffraction spots. If it is a temperature-dependent effect, it is called thermal diffuse scattering. 

Fig. 11. Diffraction pattern, at 130 volts or 1.07 A., from several layers of o.xygen molecules adsorbed upon the nickel ( r3 stal. The pattern shows a set of diffuse spots in the B-azimuth at their maximum intensitj ...

The widths of the diffuse spots along the director and perpendicular to it are inversely proportional to the correlation lengths. For some reason, main-chain LCPs very often show SmC fluctuations in the nematic phase and when they crystallize, these diffuse spots usually condense into Bragg reflections. 

Fig. 8. a X-ray scattering pattern of a fiber of an organometallic main-chain LCP quenched from the nematic phase, b Schematic representation of a. (a) = wide angle diffuse ring (b) = diffuse spots due to the SmC fiuctuations (c) = equidistant diffuse streaks (d) = other weak diffuse spots e = faint lines due to a slight crystallization... 

Let us now turn to another type of fluctuations which very often affect the SmA phase of side-chain LCPs [la,b, 30]. Figure 12 also shows some diffuse spots (d) located in the same reciprocal planes perpendicular to the director as the smectic reflections. Because of the uniaxial symmetry of the SmA phase, these diffuse spots actually represent the intersection of diffuse tori with the Ewald sphere. These diffuse tori arise from a transverse... 

Nevertheless, the 101 diffuse spots being quite broad, this 2-dimensional ordering is only correlated over a short distance. Its correlation length is only about 50 A. Besides, although the smectic period d is well defined, the modulation wave vector a is submitted to large fluctuations. 

We need to explain why we only observe the 102 diffuse spot. We could have expected that the 101 diffuse spot should be stronger than the 102 . This can be explained by considering that the undulations only affect a part of the layer so that the structure factor governing this modulation will be different from that governing the smectic reflection intensities. For simplicity, the electron density profile of the smectic layer may here be represented by step functions (Fig. 16). 

Now, the very weak intensity of the 103 diffuse spot and the absence of the higher order ones can be explained by the model of second type disorder developed by Guinier [9a]. In contrast with thermal fluctuations (which is a first... 

Fig. 5.7.2 presents the experimental results of Pindak et a/. on free standing films. The /-scan profile in the phase is a diffuse ring independent of the angle /. As hexatic ordering develops, the ring exhibits a sixfold modulation, which eventually breaks up into six diffuse spots. 

On the other hand, the X-ray diffraction patterns obtained for copolyester synthesized from terephthalic acid and an equimolecu-lar mixture of bis acetates of methylhydroquinone and pyrocatechol showed not only two pronounced cresc gts but also two diffuse spots... 

As shown in Fig. 6.2(b), we can see four relatively sharp spots just below and just above the equator, in addition to the intense diffuse spots. This suggests that crystalline order is already formed in part at 70°C, below the glass transition temperature of the bulk sample, although the crystalline structure is accompanied by a large degree of disorder. 

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