Mechanical spectrometry

On the other hand, water uptake is a continuous problem for polyimides and particularly for polynadimides [133]. Dynamic mechanical spectrometry (viscoelastic measurements) have been used to investigate the network degradations due to hydrolytic process [134]. It was shown on a special PMR resin (AFR 700 B) that network reformations are possible through post-curing. In addition, for fluorinated systems, 19F NMR can be used to follow the hydrolysis of the im-ide groups [135]. 

Morales, A., and Kokini, J.L. (1997). Glass transitions of soy globulins using differential scanning calorimetry and mechanical spectrometry. Biotechnol. Prog. 13, 624-629. 

If G and G" are studied as a function of frequency (a technique sometimes known as mechanical spectrometry), it is usually found that G increases sharply with frequency, to a new plateau value, whereas the response of G" is less pronounced and it may even go through a shallow maximum and then decrease. The frequency at which G is half-maximal corresponds approximately to t, the shear stress rate at which the velocity is half-maximal. This is easily understood on a molecular basis, since t is the rate at which the polymer molecules can reorientate themselves. As a modulus, G has dimensions of pressure Ji... 

In addition to the bulk Tg, siower relaxation was assigned to polymer chains close to the polymer-filler interface, whose mobility was restricted by the physical interactions. The existence of an interfacial layer was proposed to explain the DSC results (showing a double step in heat capacity) and TSC/DDS measurements (distinguishing two well-defined dielectric relaxation processes). These results confirmed earlier studies by dynamic mechanical spectrometry, where a second tan 5 peak, observed at 50 to 100°C above the mechanical manifestation of Tg, was attributed to the glass transition of an interfacial polymer layer with restricted mobiUty [Tsagaropoulos and Eisenburg, 1995],... 

The influence of the vinyl content on the viscoelastic behaviour of polybutadienes is shown in Figure 4. Measurements of tan S, the phase angle between stress and strain under sinusoidal deformation, have been performed by Dynamic Mechanical Spectrometry (Rheometrics). Looking at the shift along the temperature axis due to the different vinyl content, a maximum vinyl content of 72% has been chosen, since beyond this limit the polymer can hardly be regarded as a rubber. 

Perez, J., Investigation of polymer materials using mechanical spectrometry, Vysokomolek. Soedin., 1998, vol. B40, no. 1. pp. 102-135 (in Russian). 

To determine the movements of the whole chain and those of subchains, various techniques are accessible and available to the experimenter, including dielectric spectroscopy and mechanical spectrometry. Dielectric techniques are suitable for the study of polymers in a wide range of frequencies (between 10 Hz and 10 ° Hz), while the mechanical dynamic characterization of polymers provides access to long relaxation times (>10 s) through creep and stress relaxation tests. 

Alberola N, Cavaille J, Perez J. Mechanical spectrometry of alpha-relaxations of high-density polyethylene. J Polym Sci Part B Polym Phys 1990 28 569-86. 

The physical states that gliadin, glutenin and zein (com protein) encounter during processing, have been visualized in state diagrams, summarizing the information collected on protein phase transitions observed by means of DSC and mechanical spectrometry (small-amplitude oscillatory measurements at atmospheric pressure and under high pressure). 

Reaction mechanisms, infrared spectroscopy, and mass spectrometry ... 

Molecular ion (Section 13 22) In mass spectrometry the species formed by loss of an electron from a molecule Molecular orbital theory (Section 2 4) Theory of chemical bonding in which electrons are assumed to occupy orbitals in molecules much as they occupy orbitals in atoms The molecular orbitals are descnbed as combinations of the or bitals of all of the atoms that make up the molecule Molecularity (Section 4 8) The number of species that react to gether in the same elementary step of a reaction mechanism... 

The nebulization concept has been known for many years and is commonly used in hair and paint spays and similar devices. Greater control is needed to introduce a sample to an ICP instrument. For example, if the highest sensitivities of detection are to be maintained, most of the sample solution should enter the flame and not be lost beforehand. The range of droplet sizes should be as small as possible, preferably on the order of a few micrometers in diameter. Large droplets contain a lot of solvent that, if evaporated inside the plasma itself, leads to instability in the flame, with concomitant variations in instrument sensitivity. Sometimes the flame can even be snuffed out by the amount of solvent present because of interference with the basic mechanism of flame propagation. For these reasons, nebulizers for use in ICP mass spectrometry usually combine a means of desolvating the initial spray of droplets so that they shrink to a smaller, more uniform size or sometimes even into small particles of solid matter (particulates). 

In a similar fashion. Thermally Stimulated Current spectrometry (TSC) makes use of an appHed d-c potential that acts as the stress to orient dipoles. The temperature is then lowered to trap these dipoles, and small electrical currents are measured during heating as the dipoles relax. The resulting relaxation maps have been related to G and G" curves obtained by dynamic mechanical analysis (244—246). This technique, long carried out only in laboratory-built instmments, is available as a commercial TSC spectrometer from Thermold Partners L.P., formerly Solomat Instmments (247). 

The most promising approach to laboratory techniques for predicting performance is to understand the mechanism of failure and then use iastmmental methods to study the susceptibiUty of a coating to failure. The most powerful tool available now is the use of esr spectrometry to monitor the rate of free-radical appearance and disappearance (117—119) (see Magnetic spin resonance). 

In looking for the mechanism, many intermediates are assumed. Some of these are stable molecules in pure form but very active in reacting systems. Other intermediates are in very low concentration and can be identified only by special analytical methods, like mass spectrometry (the atomic species of hydrogen and halogens, for example). These are at times referred to as active centers. Others are in transition states that the reacting cheimicals form with atoms or radicals these rarely can be isolated. In heterogeneous catalytic reaction, the absorbed reactant can... 

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

In addition to the wet and optical spectrometric methods, which are often used to analyse elements present in very small proportions, there are also other techniques which can only be mentioned here. One is the method of mass spectrometry, in which the proportions of separate isotopes can be measured this can be linked to an instrument called a field-ion microscope, in which as we have seen individual atoms can be observed on a very sharp hemispherical needle tip through the mechanical action of a very intense electric field. Atoms which have been ionised and detached can then be analysed for isotopic mass. This has become a powerful device for both curiosity-driven and applied research. 

Surface analysis has made enormous contributions to the field of adhesion science. It enabled investigators to probe fundamental aspects of adhesion such as the composition of anodic oxides on metals, the surface composition of polymers that have been pretreated by etching, the nature of reactions occurring at the interface between a primer and a substrate or between a primer and an adhesive, and the orientation of molecules adsorbed onto substrates. Surface analysis has also enabled adhesion scientists to determine the mechanisms responsible for failure of adhesive bonds, especially after exposure to aggressive environments. The objective of this chapter is to review the principals of surface analysis techniques including attenuated total reflection (ATR) and reflection-absorption (RAIR) infrared spectroscopy. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and secondary ion mass spectrometry (SIMS) and to present examples of the application of each technique to important problems in adhesion science. 

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