Sampling methods films, preparation

ETEROAROMATics FURAN AND THIOPHENE. The chemical transformation of thiophene at high pressure has not been studied in detail. However, an infrared [441,445] study has placed the onset of the reaction at 16 GPa when the sample becomes yellow-orange and the C—H stretching modes involving sp carbon atoms are observed. This reaction threshold is lower than in benzene, as expected for the lower stability of thiophene. The infrared spectrum of the recovered sample differs from that of polythiophene, and the spectral characteristics indicate that it is probably amorphous. Also, the thiophene reaction is extremely sensitive to photochemical effects as reported by Shimizu and Matsunami [446]. Thiophene was observed to transform into a dark red material above 8 GPa when irradiated with 50 mW of the 514.5-nm Ar+ laser line. The reaction was not observed without irradiation. This material was hypothesized to be polythiophene because the same coloration is reported for polymeric films prepared by electrochemical methods, but no further characterization was carried out. 

Prepare the sample, if not readily available, in the form of a film approximately 1 mm thick or less for rigid polymers or 4 mm thick for flexible polymers. Film preparation methods include casting from solution, milling, or compression molding (Note 1). 

The surface of a solid sample interacts with its environment and can be changed, for instance by oxidation or due to corrosion, but surface changes can occur due to ion implantation, deposition of thick or thin films or epitaxially grown layers.91 There has been a tremendous growth in the application of surface analytical methods in the last decades. Powerful surface analysis procedures are required for the characterization of surface changes, of contamination of sample surfaces, characterization of layers and layered systems, grain boundaries, interfaces and diffusion processes, but also for process control and optimization of several film preparation procedures. 

The first samples examined were prepared by the method developed by Smith et al. [70, 71] and by Matsuo [72]. Sample films of a thickness of ca. 100 pm were obtained by drying a gel which was obtained by quenching a 0.4 g/dl decalin solution of linear polyethylene with a molecular weight of 3 x 106 from 140 °C in ice-water. The samples thus obtained could be drawn to a very high extent because of very few intermolecular chain entanglements. However, since they could not be drawn highly in one step, they were drawn 10 times at the first step in a silicon oil bath at 145 °C at a rate of 1.6 times/min and then at the second step they were drawn so that the final draw ratio was 50,100, and 150 times. 

Transmission Electron Microscopy. Films of all samples designated R were obtained by evaporation of toluene from solutions of the block copolymers and were observed without staining using a Hitachi Hu-125 or a JEOL JEM 100 S electron microscope. Methods of preparing the films have been described previously (24). So far, we have obtained evidence for microphase separation in only the four highest molecular-weight samples by TEM. We have not obtained continuous films of the lower molecular-weight samples we plan to examine sections of these samples later. Because of the very small compatibility of styrene and polydimethylsiloxane, however, we expect phase separation in all of these samples. 

Another method of preparing the sample is to disperse it in linseed oil, which is then thinned with white spirit. The dispersion is spread over a microscope slide that is immersed in white spirit for a few minutes to remove the oil. After drying the slide a thin layer of carbon is deposited on the specimen to form a supporting film. Finally this is floated off on water as before and picked up on a grid for examination [91 ]. 

In the present work, intensity of ultramarine Raman spectra have been enhanced by the order of magnitude with solid nanosized Ag particles. Model samples have been prepared as powder mixtures of the pigment and silver particles without any compressing pretreatment. This makes the sample preparation process more easy in contrast to a more traditional way based on SERS-active film from colloidal solution of nanosized Ag particles. The technique does not require much sample material from art objects and preparation of aqueous suspension from a sample. Taking into consideration the low solubility of art pigments in water we propose the sensitive method of pigment identification in real art objeets. 

Liquid and gas samples do not need much preparation, but special cells to contain the samples are often necessary. The simplest method to prepare a liquid sample is to make a capillary thin film of the liquid. The capillary thin film is made by placing a drop of liquid on a KBr plate and sandwiching it with another KBr plate. This method, however, is not suitable for volatile liquids. Liquid cells can be used for volatile liquid and toxic liquid samples, particularly for quantitative analysis. The spacing between the bottom and the top of liquid cell is typically from 1 to 100 /u.m. The cell is made of an infrared-transparent material. Typically, KBr is used however, KBr should not be selected as the material for holding samples containing water because water dissolves KBr. Instead, ZeSe or AgCl should be used because they are infrared-transparent but not water soluble. Cells for gas samples are structurally similar to cells for liquid but the dimension is much larger. 

K.. The advantages of this method are the Increased surface area presented by the particulate sample relative to the film and the removal of film preparation procedure dependence. 

A transparent film prepared from a poorly dispersed composite by the same method is shown in Figure 6. Chunks of carbon black, about 2irin diameter are readily visible. During micronization, fracture could conceivably occur in the middle of a large carbon black chunk, leaving the uncoated surface exposed. In the well dispersed material, fracture through the smaller carbon black aggregates seems less likely, thus the surface of this sample powder probably has less exposed carbon black. 

Spiess et al. [7] developed a multidimensional DECODER (direction exchange with correlation for orientation-distribution evaluation and reconstruction) method to measure and correlate NMR frequencies at two different sample orientations. Through this correlation, the spectra contain the equivalent of information on two Euler angles that describe the orientation of a given molecular segment. Many features of the orientation distribution are directly reflected in the intensity distribution of the 2D spectrum, from which the width of the orientation distribution of certain axes can immediately be read. The multidimensional DECODER NMR experiments are applied to drawn PET fibers and thin PET films prepared under different processing conditions. 

Depending on the method of preparation, the surface of a diamond film is either functionalized aheady, for example, covered by hydrogen atoms, or it exhibits an array of so-called surface dimers (it-bonds arising from reconstruction). The latter case is mostly found for samples that have been subject to a secondary thermal treatment to remove their initial, usually inhomogeneous surface functionalization. 

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