STATIC AND DYNAMIC LIGHT-SCATTERING-STUDIES OF DEXTRAN FROM LEUCONOSTOC-MESENTEROIDES IN THE DILUTE REGION

Autor(en): NORDMEIER, E
XING, H
LECHNER, MD
Stichwörter: DIFFERENT TEMPERATURES; Polymer Science; POLYMERS
Erscheinungsdatum: 1993
Herausgeber: HUTHIG & WEPF VERLAG
Journal: MAKROMOLEKULARE CHEMIE-MACROMOLECULAR CHEMISTRY AND PHYSICS
Volumen: 194
Ausgabe: 11
Startseite: 2923
Seitenende: 2937
Zusammenfassung: 
Dextrans with mass-average molar masses 8 . 10(4) g/mol less-than-or-equal-to M(w)BAR less-than-or-equal-to 10(8) 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]z1/2 and A2 on the mass-average molar mass, M(w)BAR, can be well described by the power laws [S2]z1/2 = K(S) . M-W(nu)SBAR and A2 = K(A) . M-W(nu)ABAR. The exponent nu(S) is independent of the temperature T, while nu(A) decreases as T is raised. Dynamic light scattering (DLS) yields the apparent diffusion coefficient, D(app)(q, c), and the hydrodynamic radius, R(h), where q is the wave vector and c the polymer concentration. For small q, a plot of D(app) (q, c) versus q2 . [S2]z gives a straight line. The intercept D(z) (c) = lim(q-->0) D(app) (q, c) represents the centre-of-mass translational diffusion coefficient. Its dependence on the concentration, c, can be well simulated by the relation D(z)(c) = D(z,0)[1 k(D,2).C]. Here, k(D,2) is the second hydrodynamic virial coefficient and D(z,0) the z-average of the translational diffusion coefficient at infinite dilution. The analysis of the k(D,2)-data shows that dextran molecules behave rather as interpenetrable than as non-interpenetrable spheres. The density rho = (3 M(W)BAR)/(N(A) . 4 piR(h)3) proves to be a measure for the degree of penetration; rho decreases with increasing M(w)BAR, indicating that penetration becomes easier at higher molar masses.
ISSN: 0025116X

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