Molecular mobility measurement kinetics

A study of maltodextrin and inulin gels was carried out by cross-relaxation spectroscopy, TIP (H) measurements, and a wideline separation experiment (WISE).132 During ageing, the amount of immobilized polymer increases owing to the formation of crystalline regions, but it is not associated with change in molecular mobility. Different kinetics were found for maltodextrin and inulin gels.132... 

The kinetics of the OSO4 treatment as revealed by microhardness measurements has been examined. The increase in microhardness has been explained in terms of the large reduction in molecular mobility of the amorphous, interlamellar layers, Chlorosulphonation produces an initial microhardening of the amorphous phase, in which reaction time, temperature and the molecular weight play an important role. The OSO4 reaction induces an additional microhardening at the surface of crystalline lamellae. Results reveal that Ha increases, after the above chemical reactions, from nearly zero up to values of 300 MPa (Baltd Calleja et ai, 1997). 

D)mamic properties of water determine several important kinetic processes that determine key deteriorative quality changes and hence commercial food shelf-lives. Foods are mostly in a state of thermodynamic instability and kinetic barriers do exist as water molecules are transferred from phase to phase and state to state. Molecular mobility of water in different domains can be measured by methods such as NMR which, as with a, involves the ability to become vapor and requires a thermodynamic equilibrium. In a non-equilibrium situation, the use of relative vapor pressure (RVP) has been proposed (Slade and Levine, 1988). 

Three types of methods are used to study solvation in molecular solvents. These are primarily the methods commonly used in studying the structures of molecules. However, optical spectroscopy (IR and Raman) yields results that are difficult to interpret from the point of view of solvation and are thus not often used to measure solvation numbers. NMR is more successful, as the chemical shifts are chiefly affected by solvation. Measurement of solvation-dependent kinetic quantities is often used (<electrolytic mobility, diffusion coefficients, etc). These methods supply data on the region in the immediate vicinity of the ion, i.e. the primary solvation sphere, closely connected to the ion and moving together with it. By means of the third type of methods some static quantities entropy and compressibility as well as some non-thermodynamic quantities such as the dielectric constant) are measured. These methods also pertain to the secondary solvation-sphere, in which the solvent structure is affected by the presence of ions, but the... 

The thermodynamic dead volume includes those static fractions of the mobile phase that have the same composition as the moving phase, and thus do not contribute to solute retention by differential interaction in a similar manner to those with the stationary phase. It is seen that, in contrast to the kinetic dead volume, which by definition can contain no static mobile phase, and as a consequence is independent of the solute chromatographed, the thermodynamic dead volume will vary from solute to solute depending on the size of the solute molecule (i.e. is dependent on both ( i )and (n). Moreover, the amount of the stationary phase accessible to the solute will also vary with the size of the molecule (i.e. is dependent on (%)). It follows, that for a given stationary phase, it is not possible to compare the retentive properties of one solute with those of another in thermodynamic terms, unless ( ), (n) and (fc) are known accurately for each solute. This is particularly important if the two solutes differ significantly in molecular volume. The experimental determination of ( ), (n) and( ) would be extremely difficult, if not impossible In practice, as it would be necessary to carry out a separate series of exclusion measurements for each solute which, at best, would be lengthy and tedious. 

The glass transition temperature can be measured in a variety of ways (DSC, dynamic mechanical analysis, thermal mechanical analysis), not all of which yield the same value [3,8,9,24,29], This results from the kinetic, rather than thermodynamic, nature of the transition [40,41], Tg depends on the heating rate of the experiment and the thermal history of the specimen [3,8,9], Also, any molecular parameter affecting chain mobility effects the T% [3,8], Table 16.2 provides a summary of molecular parameters that influence the T. From the point of view of DSC measurements, an increase in heat capacity occurs at Tg due to the onset of these additional molecular motions, which shows up as an endothermic response with a shift in the baseline [9,24]. 

We have shown that combining ion mobility spectrometry (IMS) equipment with mass spectrometry (MS) provides a powerful tool to examine the three-dimensional structure of polyatomic ions by measuring collision cross sections of mass identified ions. The technique is particularly useful in conjunction with molecular modeling or electronic structure calculations. Further, we have reviewed applications where the IMS-MS equipment is used to obtain kinetic and thermo chemical data of ions. 

In addition, the combination of these EBL-fabricated Pd model catalysts and UHV molecular beam system has allowed the first experimental confirmation that surface diffusion over the whole particle must be taken into account to describe the global kinetics, and thus support the theoretically predicted communication effects between different facets on a nanoparticle [4, 146, 148, 149]. These experiments also allowed measurement of the surface mobility of oxygen under reaction conditions [83,150]. On a given nanoparticle, regions with locally different adsorption or reaction properties (such as different crystallographic orientations, i.e., facets) can communicate. 

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