Dextran probe diffusion

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]. 

Single-chain diffusion of dextran probe molecules in various matrix polymers was examined by Daivis, et a/. (38), De Smedt, et a/. (43), and Tinland and Borsali (44), as seen in Figure 8.27. The value of Dg in aqueous 20.4 kDa dextran solutions of an 864 kDa dextran was determined with QELSS by Daivis, et aL(38). QELSS spectra were bimodal, the slower mode corresponding to Dg Dg (c) follows a simple exponential in c reasonably well. The D of 71,148, and 487 kDa dextran probes... 

Phillies, et al. observed probe diffusion in aqueous dextran(12). Representative measurements of Dp and rj for two polymer molecular weights appear in Figure 9.5 together with fits to stretched exponentials. Dextran concentrations covered 0 < c < 250 g/1, using nine different dextran samples. Probes were polystyrene spheres with radius 20 or 230 nm solution viscosities were obtained... 

De Smedt, etal. used FRAP to examine diffusion of fluorescein-labeled dextrans and polystyrene latex spheres through hyaluronic acid solutions(17). Dextrans had molecular weights 71, 148, and 487 kDa. The hyaluronic acid had and of 390 and 680 kDa. The dextran diffusion coefficients depend on matrix polymer c as stretched exponentials in c, as seen in Figure 9.9b. Hyaluronic acid solutions are somewhat more effective at retarding the larger dextran probes. Viscosities for these solutions were reported by De Smedt, et a/. (18). The concentration dependence of rj is stronger than the concentration dependence of Dp of the polystyrene spheres, which is in turn stronger than the concentration dependence of Dp of the dextrans. Spheres and dextrans both diffuse more rapidly than expected from the solution viscosity and the Stokes-Einstein equation. 

R. Furukawa, J. L. Arauz-Lara, and B. R. Ware. Self-diffusion and probe diffusion in dilute and semidilute solutions of dextran. Macromolecules, 24 (1991), 599-605. 

G. D. J. Phillies and C. A. Quinlan. Glass temperature effects in probe diffusion in dextran solutions. Mflcromo/ecMto, 25 (1992), 3110-3116. 

As part of a study of probe diffusion and tracer chain diffusion in dextran solutions, Furukawa, et al. report the viscosity of 40 and 150 kDa dextrans in aqueous solution(20). Viscosities measured with Ubbelohde viscometers reached 100 cP concentrations extended up to 400 g/1. Their measurements and functional fits appear as Figure 12.4. While t (c) is described reasonably weU by stretched exponentials in c, for solutions of the 150 kDa dextran at small concentrations the measured viscosities clearly lie below the stretched-exponeniial fit. 

Tinland and Borsali [123] used FRAP and QELS to measure Dp of 433 kDa dextran in aqueous solutions of 310 kDa polyvinylpyrrolidone (PVP) for 0 < c < 120g/L. M ,/Mn was 1.5 for the matrix polymer but ca. 1.9-1.95 for the probes. Dp from the two techniques do not agree. We analyzed Dp from FRAP measurements, because FRAP does not require the detailed model assumptions needed to relate the QELSS spectrum to diffusion coefficients. Tinland and Borsali s data agree well with stretched exponentials in c. 

As part of a study of translational and rotational diffusion of rodlike probes in solutions of neutral polymers, Cush, Russo, and collaborators report q c) for two dextrans and one hcoll in aqueous solution(17,18). Concentrations ranged up to 10-30 wt%. In almost all solutions j7/ 7o < 100 was found. For each polymer, r] c) was htted accurately hy a stretched exponential, as shown in Figure 12.2. 

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