Münster 1997 – wissenschaftliches Programm
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CP: Chemische Physik
CP 13: Poster zur Sitzung CP3
CP 13.4: Poster
Montag, 17. März 1997, 18:30–21:15, FBH
Orientation diagram for lamellar PS-b-PI diblock copolymers under large amplitude oscillatory shear flow — •Daniel Maring, Yuanming Zhang, Heike Leist, and Ulrich Wiesner — MPI f. Polymerforschung, Ackermannweg 10, 55128 Mainz
The strain dependence of the lamellar orientation is investigated for a nearly symmetric polystyrene-polyisoprene diblock copolymer of low molecular weight under large-amplitude oscillatory shear flow near the order-disorder transition temperature (TODT). In the intermediate frequency regime of the dynamic shear viscosity for low strains a threshold value for the formation of the perpendicular orientation is observed, that depends on frequency and temperature. Below this critical strain parallel orientation is found. From these results for the first time an orientation diagram as a function of strain and frequency is constructed. While one can identify critical shear frequencies ωc and ωd separating the different frequency regimes of orientation at larger strain, at low strain values parallel orientation is observed irrespective of frequency.