Chain conformation in sheared polymer melts as revealed by SANS

Towards a rheological classification of flow induced crystallization experiments of polymer melts

“…It should be noted that due to the CCR mechanism, as well as the polydisperse nature of the melt, the orientational ordering of the (HMW) chains is arrested to a specific magnitude (as reflected by an approximately constant orientation angle for 1 s rep \_ c\1=s s as discussed above). This argument is supported by SANS measurement in shear flow (Muller and Picot 1992;Muller et al 1993), which reveal that the deviation from the spherical coil conformation is rather weak and limited to a certain extent for 1 s rep \_ c\1=s s . The latter is in agreement with model predictions (McLeish 2002).…”

Direct Measurement of the Confining Forces Imposed on a Single Molecule in a Concentrated Solution of Circular Polymers

“…Such behavior observed in the large-displacement regime may be related to the phenomenon of convective constraint release, predicted by certain theories to be important in understanding the nonlinear response of polymeric liquids. 35,[41][42][43][44] With linear DNA we also observed a subsequent increase in dF/dy for the 13 µm/s rate, which may be due to the probe encountering new entanglements. No such feature was observed with the circular DNA, again suggesting that entanglements tend to more easily slip off the probe as it is displaced.…”

Tube theory of entangled polymer dynamics

“…Extensional measurements were ®rst made by Boue [51]. The shear case for polystyrene was reported by Muller et al [49]. The remarkable result suggested that the maximum degree of anisotropy, de®ned as the ratio of the e ective radii of gyration in the¯ow and¯ow-gradient directionÐx and y in the de®nitions of the shear rate tensor of equation (31)Ðdid not exceed about 1.8, even for large deformations at rates such that _ ® ®½ d ¾ 1.…”