Intrinsic mobility

Factors which affect the inherent or intrinsic mobility of a single chain considered on its own. 

Various diffusion coefficients have appeared in the polymer literature. The diffusion coefficient D that appears in Eq. (3) is termed the mutual diffusion coefficient in the mixture. By its very nature, it is a measure of the ability of the system to dissipate a concentration gradient rather than a measure of the intrinsic mobility of the diffusing molecules. In fact, it has been demonstrated that there is a bulk flow of the more slowly diffusing component during the diffusion process [4], The mutual diffusion coefficient thus includes the effect of this bulk flow. An intrinsic diffusion coefficient, Df, also has been defined in terms of the rate of transport across a section where no bulk flow occurs. It can be shown that these quantities are related to the mutual diffusion coefficient by... 

As described above, there is a striking correlation between the creation and annealing kinetics of metastable defects in a-Si H and the motion of bonded hydrogen. There are essentially two classes of models proposed to both account for this agreement and to explain the microscopic mechanisms for hydrogen diffusion. One type of model assumes that the hydrogen is intrinsically mobile and moves from one bonded position to another... 

Although these approaches seem to be similar, the former method has several limitations it should be recognized that intrinsic mobility (yu,A ) depends on the ionic strength of the buffer, as shown in Ref. 17. Also, the activity coefficients of the zwitterions could not be calculated via the De-bye-Hiickel equation, and other methods, such as melting point depression, should be used to obtain the activity coefficients of the zwitterions (31). On the other hand, the latter method is directly applicable to the zwitterions to obtain their acidity constants. 

Another cause of error is the intrinsic mobility of multiply charged species. The mobility of doubly charged species is not always double the mobility of a single-charged species, as is the case with betahistine (14). Although some groups used this invalid assumption (18,28), this is one cause error. 

Carman P.C. (1968) Intrinsic mobilities and independent fluxes in multicomponent isothermal diffusion, I simple Darken systems II complex Darken systems. /. Phys. Chem. 76, 1707-1721. 

The results of experimental studies of the sorption and diffusion of light hydrocarbons and some other simple nonpolar molecules in type-A zeolites are summarized and compared with reported data for similar molecules in H-chabazite. Henry s law constants and equilibrium isotherms for both zeolites are interpreted in terms of a simple theoretical model. Zeolitic diffusivitiesy measured over small differential concentration steps, show a pronounced increase with sorbate concentration. This effect can be accounted for by the nonlinearity of the isotherms and the intrinsic mobilities are essentially independent of concentration. Activation energies for diffusion, calculated from the temperature dependence of the intrinsic mobilitieSy show a clear correlation with critical diameter. For the simpler moleculeSy transition state theory gives a quantitative prediction of the experimental diffusivity. 

Estevez R, Van der Giessen E (2005) In Kausch HH (ed) Intrinsic mobility and toughness of polymers. (Advances in Polymer Science). Springer, Berlin Heidelberg New York 188 195... 

Here fix is the chemical potential, and B Ca = La is the phenomenological coeflScient of irreversible thermodynamics. Ba is the intrinsic mobility of A. This expression can be rewritten as... 

Dextran oligomers with a rather small molecular mass exhibit an intrinsic mobility due to the label. On the other hand, they are too small to interact with the sieving matrix and migrate therefore in a counterelectroosmotic way, as in free CZE the smallest oligomer with the highest mobility is last to be transported by the EOF to the detector. This is shown as case A in Fig. 17. 

Dextrans of medium molecular mass (e.g. around 21,000 g mol-1) do not have any intrinsic mobility, the charge introduced by the label does not have any influence with an analyte of this molecular mass. Interaction with the sieving matrix does still not exist, consequently this molecule is transported by the EOF like an uncharged molecule in CZE (case B in Fig. 17). 

Dextrans of high molecular mass also do not have an intrinsic mobility, but are large enough to interact with the migrating sieving medium. The longer the analyte chain, the more intensive the contact with the matrix, and the slower its transport to the detector in this counterelectroosmotic technique (case C in Fig. 17). 

Quite often the mobilities determined for a given molecule, e.g. rabrene or pentacene, differ for different devices in different laboratories, reflecting the problems related to the extraction of the mobility data from the electrical characteristics. Typically, these characteristics are not only defined by the mobilities but also by the contact resistance and of course the presence of domain boundaries defects and impirrities in the organic semiconductor. The determination of the true intrinsic mobility of an organic semiconductor is still a challenge, which has only been overcome in a very few cases. 

---