Polyethylene oxide probe diffusion

Lin used QELSS to study diffusion of 155 and 170 nm nominal radius titania spheres in a melt of 7500 Da polyethylene oxide(ll). Over a 75 °C temperature range, Dp changes by nearly two orders of magnitude. Comparison was made with the viscosity obtained using a cone-and-plate viscometer. The observed microviscosities were substantially less than the measured viscosity. An extrapolation procedure based on the apparent activation energy, as inferred from the temperature dependence of rj, was used to estimate an effective shear rate for probe diffusion > 10 s , corresponding via y D/L to probe diffusion over atomic distances. Such distances would rationally be fundamental if the unit step for probe diffusion in a polymer melt were the displacement of a single layer of polymer chains. 

Cheng, et al. used FRAP to monitor the diffusion of extremely small probes (1 < < 20 nm) in solutions of guar galactomannan and polyethylene oxide(24). 

Phillies reports on the diffusion of bovine serum albumin through solutions of 100 kDa and 300 kDa polyethylene oxides(27). The Dp value depended measurably on the probe concentration. At elevated polymer c and low protein concentration. Dp was as much as a third faster than expected from the c-dependent solution fluidity. With increasing protein concentration. Dp fell toward values expected from the macroscopic r. This study pushed the technical limits of then-current light-scattering instrumentation. 

Ullmann, et al.O ) extended Ullmann and Philhes(31) to study probe diffusion of carboxylate-modified polystyrene spheres in aqueous polyethylene oxide Triton X-100. The Dp for most sphere matrix combinations follows a stretched exponential in c, as seen in Figure 9.18. However, Dp of the 655 nm diameter spheres shows re-entrant behavior, both in the 18.5 kDa polymer and to a lesser extent... 

Figure 4.2 — (A) Schematic diagram of an ammonia-N-sensitive probe based on an Ir-MOS capacitor. (Reproduced from [20] with permission of the American Chemical Society). (B) Pneumato-amperometric flow-through cell (a) upper Plexiglas part (b) metallized Gore-Tec membrane (c) auxiliary Gore-Tec membrane (d) polyethylene spacer (e) bottom Plexiglas part (/) carrier stream inlet (g) carrier stream outlet. (C) Schematic representation of the pneumato-amperometric process. The volatile species Y in the carrier stream diffuses through the membrane pores to the porous electrode surface in the electrochemical cell and is oxidized or reduced. (Reproduced from [21] with permission of the American Chemical Society).

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