Molecular Orientation and Deformation of Polymer Solutions under Shear:  A Flow Light Scattering Study

Abstract

The conformational characteristics of polymer coils in dilute solution under shear flow were investigated by means of wide angle laser light scattering in an apparatus similar to one used by Cottrell, Merrill, and Smith (J. Polym. Sci., Polym. Phys. Ed. 1969, 7, 1415). 1 The polymer solution was subjected to steady, homogeneous shear flow in the annulus between concentric cylinders by rotation of the inner cylinder. By examining the angular dependence of the scattered light intensity during shear, the orientation and the lengths of the major and minor axes of the deformed polymer molecules in solution were determined quantitatively. The solutions studied were linear polystyrenes of various molecular weights dissolved in the viscous solvent dioctyl phthalate near the Θ temperature. The shear rate dependence of the orientation angle of the deformed molecules was found to agree well with Zimm model predictions. The elastic dumbbell, Rouse, and Zimm models, however, substantially overpredict the degree of deformation of the polymer coils. This is in agreement with results of Link and Springer (Makromol.

Single-Polymer Dynamics in Steady Shear Flow

“…Previous experiments with light and neutron scattering indicated that polymers did not deform substantially in shear (7)(8)(9). However, this seems to be due to the small shear rates applied to the molecule in these experiments.…”

“…The development of nanoscale manipulation techniques (2) has made it possible to directly address single atoms or molecules and probe their mechanical properties. It has been shown that individual polymers may be stretched between the tip of an AFM cantilever and a substrate surface (3)(4)(5)(6)(7)(8)(9)(10)(11)(12). In these studies, polymers were coupled either by specific receptor ligand systems, which were covalently attached to the polymers (8), or by nonspecific adsorption to the tip and the substrate (3, …”

Free surface flows of polymer solutions with models based on the conformation tensor

“…If they are rigid, the contraction occurs at lower Weissenberg number because it is caused by flow rather than molecular relaxation. Because current experimental evidence is inconclusive [9,58,59], it will take further experiments to answer the question of whether or not the molecular conformation tensor contracts. …”

Excluded volume effects on the structure of a linear polymer under shear flow

“…However, several scattering experiments have been performed, mainly Light Scattering (LS), with the aim to investigate the global properties of the chain such as the orientation and the deformation of the coil by the flow [14][15][16][17][18][19][20]. The effect of EV interaction over global chain properties has been discussed in a series of recent LS studies [18][19][20] where some systematic trends were reported. For dilute solutions in shear flow at a fixed reduced shear rate, a systematic weakening of the alignment of the main axis of the chain in the flow direction has been observed for increasing solvent quality.…”