ISSN:
0025-116X
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Dextrans with mass-average molar masses 8.104 g/mol ≤ M̄w ≤ 108 g/mol have been studied in water by means of static and dynamic light scattering at different temperatures. Static light scattering (SLS) yields the z-average mean-square radius of gyration, 〈S2〉z and the second virial coefficient A2. It is found that the dependences of 〈S2〉z1/3 and A2 on the mass-average molar mass, M̄w, can be well described by the power laws 〈S2〉z1/3 = KS · M̄wsv and A2 = KA · M̄wAv. The exponent vs is independent of the temperature T, while vA decreases as T is raised. Dynamic light scattering (DLS) yields the apparent diffusion coefficient, Dapp (q,c), and the hydrodynamic radius, Rh, where q is the wave vector and c the polymer concentration. For small q, a plot of Dapp (q, c) versus q2 · 〈S2〉z gives a straight line. The intercept $ D_{\rm z} (c) = \mathop {\lim }\limits_{q \to 0} D_{{\rm app}} (q,c) $ represents the centre-of-mass translational diffusion coefficient. Its dependence on the concentration, c, can be well simulated by the relation \documentclass{article}\pagestyle{empty}\begin{document}$ D_{\rm z} (c) = D_{{\rm z,}0} \left[ {1 + k_{{\rm D},2} \cdot c} \right] $\end{document}. Here kD, 2 is the second hydrodynamic virial coefficient and Dz,0 the z-average of the translational diffusion coefficient at infinite dilution. The analysis of the kD,2 -data shows that dextran molecules behave rather as interpenetrable than as non-interpenetrable spheres. The density p = (3 M̄w)/(NA · 4 π Rh3) proves to be a measure for the degree of penetration; p decreases with increasing M̄w, indicating that penetration becomes easier at higher molar masses.
Zusätzliches Material:
5 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/macp.1993.021941101
Permalink