Diffusion probe

Tokita, M Miyoshi, T Takegoshi, K Hikichi, K, Probe Diffusion in Gels, Physical Review E 53, 1823, 1996. 

IH Park, CS Johnson, DA Gabriel. Probe diffusion in polyacrylamide gels as ob-... 

G.D.J. Phillies, D. Rostcheck, and S. Ahmed Probe Diffusion in Intermediate Molecular Weight Polyelectrolytes Temperature Dependence. Macromolecules 25, 3689 (1992). 

D = D° exp(-ac ), where D is the diffusion, D represents the zero-concentration limit, c is the concentration, a and v are parameters, fits the data from a wide variety of probes and matrix polymers ( ). Several theoretical justifications for this behavior have been presented (97-1011. but it is not possible to tell yet which, if any, is uniquely correct. The treatments range from simple physical considerations (98) to treatments of hydrodynsumical interaction of probe and matrix (97,991. Other more complex and general treatments (1001 do not explicitly arrive at the stretched exponential form, but do closely fit the available data. Much more work needs to be done on probe diffusion in such transient networks. Beyond enhancing the arsenal of gel characterization, the problem is quite fundamental to a number of other important processes. 

Yet the relationship between solute chemical structure and diffusion is not always simple. Werner et al. [248] conducted fluorescence correlation spectroscopic studies of three fluorescent probes in l-butyl-3-methylimidazolium hexafluorophosphate. The probes were chosen to be of comparable molecular structure, but possessed positive, negative, and neutral charges. The authors found that while the neutral probe diffused more rapidly than the cationic probe, the anionic probe diffused the most quickly. 

Spatial Inhomogeneity of Cavities in Polymer Network Systems as Characterised by Field-Gradient NMR Using Probe Diffusant Molecules and Polymers with Different Sizes... 

Diffusion can be divided into free and restricted diffusion. A combination of NMR diffusometry and microscopy has proved useful for the study of probe diffusion in gels and emulsions (Hagslatt et al. 2003 Loren et al. 2005 Hermansson et al. 2006 Walther et al. 2006) For such studies the probe should be much larger than water so that the obstruction can be clearly observed in NMR difiusometiy. Small molecules... 

Kinetics of e -h recombination may depend on its mode if one electron is excited and this is recombined with h , the recombination rate obeys the first-order rate law, while if multiple e -h+ appears at the same time within a photocatalyst particle, the rate obeys the second-order rate law. Actually, in a femtosecond pmnp-probe diffuse reflection spectroscopic analysis of tita-nia samples, photoabsorption at 620 nm by trapped electrons showed second-order decay with a component of baseline as follows ... 

Despite the obvious importance of diffusion studies, information on these topics is still limited. The position reflects experimental difficulties and, in part, a failure to realize how useful a probe diffusion may be. It is hoped that the importance of diffusion will become apparent from the present review. 

There are alternates to probing diffusion by molecular dynamics or transition state theory. For a diffiisional path than contains a significant constriction or activation barrier, an additional force along the difiusion direction can be applied to enforce lateral difiusion pn the molecule. The hias in quantifying the difiusion that results that such an additional force injects can, in principle, be corrected-for so as to yield an estimate of the translational difiusion coefELdent in the free, unperturbed system. 

De Souza, R.A., Martin, M. Probing diffusion kinetics with secondary ion mass spectrometry. MRS Bull. 2009, 34, 907-14. 

When the probe is identical to the host, probe diffusion becomes selfdiffusion in a neat glass-former. By extrapolating the results of probe/host systems, the breakdown of SE and DSE relations in neat glass-formers is expected, and the correlation between Dtxc/ (A Osedse and n= (l — kww)... 

The probe concentration varies widely in different reports (50-5000 ng/ml). Although high concentrations increase the probe diffusion rate and reduce the hybridization time, background also increases. For radiolabeled probes, it is best to maintain relatively low... 

Informative probe diffusion alone cannot reveal structural and intermolecular interaction details because the echo decay from a probe in a heterogeneous matrix is not imique and a large number of different structures and/or interaction possibilities may give rise to the same echo decay. One way to attack this problem is to use a similar approach to the one mentioned previously, regarding water diffusion in emulsions. In order to succeed with this, however, we believe that a three-dimensional gel structure must be used for diffusion simulations. For this reason work is in progress to develop a new combination of methods, NMR diffusometry, microscopy, mathematical reconstruction, image analysis and diffusion calculations/simulations by Monte Carlo and finite element methods (to be published shortly). 

Nyden, M., Karlstrom, G., and Soderman, O. A PFG NMR self-diffusion investigation of probe diffusion in an ethyl(hydroxyethyl)cellulose matrix. Macromolecules, 32, 127,1999. 

Phillies, G.D.J. and Clomenil, D. Probe diffusion in polymer solutions under Q and good conditions. Macromolecules, 26, 167, 1993. 

S. C. De Smedt, A. Lauwers, J. Demeester, Y. Engelborghs, G. De Mey, and M. Du. Structural information on hyaluronic acid solutions as studied by probe diffusion experiments. Macromolecules 27 141-146 (1993). 

Styrene DODAB 1 2 Sonication CHP/Ee(II), 50 °C Hollow polymer spheres TEM, SEM, paramagnetic probe diffusion Kurja et al. (1993) [8]... 

Probe diffusion rates observed from parachutes or hollow polymer spheres may be indistinguishable since the probe could be bound in either a polymer bead or polymer shell with similar release characteristics. For example, only hydrophobic probes could be trapped in the polymerized vesicles synthesized by Nakache et al. Here, trapping refers to a decrease in the rate of probe release after vesicle polymerization. The trans-membrane diffusion rates of hydrophilic probes should decrease following polymerization if a polymer shell is successfully formed in the surfactant bilayer. Nakache et al. only observed a decrease in the trans-membrane diffusion rate of hydrophobic probes. This is important since the hydrophobic probe may be released from both hollow polymer spheres and polymer latices with similar release kinetics. Again, caution should be taken, as already shown by German et al. [20] in the case of the fluorescence... 

Of all the characterization methods employed to study the morphologies of polymerized vesicles, cryo TEM is perhaps the most powerful. SEM, freeze fracture TEM, QLS, and probe diffusion studies alone cannot adequately distinguish between the polymer morphologies that have been proven to occur such as between hollow polymer shells and phase separated polymer-vesicle systems. 

This approach—which uses Brinkman s equation, with an appropriate correlation to permit estimation of the hydraulic permeability from the structural characteristics of the medium—provides a straightforward method for estimating the influence of hydrodynamic screening in polymer solutions predicted diffusion coefficients for probes of 3.4 and 10 nm in dextran solutions (Pf = 1 nm) are shown in Figure 4.9. This approach should be valid for cases in which probe diffusion is much more rapid than the movement of fibers in the network, although it appears to work well for BSA diffusion in dextran solutions, even though the dextran molecules diffuse as quickly as the BSA probes [54]. 

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