Slow mode self-diffusion

Fig. 11 The dynamic structure factor C(, r) of polybutadiene star 12880 (nominally f = 128, Ma = 80kgmol ) in cyclohexane at ci = 0.016gmL and q = 0.035nm , along with the fit (solid line) from the ILT analysis. The corresponding relaxation distribution function L(ln(T)) (shown here for f i and q = 0.023gmL ) embraces the cooperative diffusion (1), the collective apparent diffusion (2), and the self-diffusion (3). The slowing-down of the middle structural mode (2) and the increase of its intensity with q are shown in the upper inset whereas the lower cartoon illustrates the liquid-like ordering [43,189]. The core regions are drawn out of scale (larger) for clarity...

We conclude this section with a discussion of possible relations between interdiffusion in polymer blends and the self-diffusion coefficients of the polymer chains, which have been proposed to interpret the Gnsager coefficient A(0) in Eqs. (78), (79) or (85), respectively. According to the slow mode theory [9, 78, 191-192] the slowly diffusing component controls interdiffusion in a blend,... 

One of the most serious obstacles in the phase equilibrium studies of polymer blends is the viscosity of the system. At temperahires limited by the degradation the self-diffusion coefficient of macromolecules is of the order of magnitude 10 to 10 m /s [Kausch and Tirrell, 1989]. As a result the phase separation is slow. To accelerate the process a low speed centrifuge, the centrifugal homogenizer (CH), with PICS has been used [Koningsveld et al, 1982]. In short, centrifugation within the immiscibility zone permits determination of binodal and critical points, while the use of PICS mode allows location of the spinodal. 

For highly concentrated polymer solutions, FCS measurements revealed subdiffusive motion as an additional mode on an intermediate timescale between the fast collective diffusion and the slow self-diffusion [24]. In such slow systems, however, FCS reaches its limits when probe motion becomes so slow that the number of molecules moving into or out of the confocal volume within the measurement time is too small to allow for reliable statistics. Increasing the measurement time is often not straightforward since all fluorescence dyes have only a limited photostability. If a dye bleaches within the confocal volume, it will fake a faster diffusional motion than its real value. Therefore, for the study of such concentrated systems, wide-field fluorescence microscopy and subsequent single molecule tracking is a much better method [120] and has been utilized to study the glass transition [87, 121]. 

In the previous study [7], we have shown that when the temperature exceeds about 55 °C, the self-diffusion coefficient approaches the value expected from the data in the cubic phase where the lateral diffusion is dominant. In this temperature range, the slow mode cannot be distinguished from the fast mode because decreases rapidly with increasing temperature, suggesting that the R x )... 

V.4. Effects of Configuration and Entanglement We also demonstrated the effect of configuration on the dynamic behavior of semidilute polymer solutions. Different results have been obtained by adding to the matrix a 4-arm star polystyrene SPS4 which was comparable with the linear test chain LPS2 in number and size. First, the self-diffusion (the slow mode) became invisible (disappeared). Second, the cooperative diffusion became faster. 

W. Brown, R. M. Johnsen, and P. Stilbs. Quasielastic light scattering (QELS) in semidilute polymer solutions. A comparison of slow-mode diffusion with self-diffusion from IT -pulsed field gradient NMR. Polym. Bull., 9 (1983), 305-312. 

CPI labeled with eosin-SCN in the non activated mode restored photophosphorylation in partially depleted EDTA-chloroplasts and fully depleted NaBr-particles (10). Wheras in the case of the EDTA-particles we could observe very slow rotational motion of the reconstituted eosin-CFI relative to the membrane, in NaBr-part ides we could not detect any rotational motion (up to 500 as) of reconstituted eosin-CFI. We also studied the rotational diffusion of another extrinsic protein of the thylakoid membrane, the ferredoxin-NADP-oxidoreductase (ll), which is probably located in the same stromal region of stacked chloroplasts as CPI and we found very rapid rotation (< 1/is). Only after addition of ferredoxin rotational correlation time decreased to 40 /is. This was interpreted to indicate formation of a ternary complex between ferredoxin-NADP-oxidoreductase ferredoxin and PSI. This revealed rather high lipid fluidy in thylakoids. We tend to assume that the low rotational mobility of the CP0-CF1 complex is caused either by self aggregation or strong interaction with other membrane proteins. 

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