Simulation of self-associating polymer systems. II. Rheological properties

Using nonequilibrium molecular dynamics (NEMD), self-associating polymer systems composed of flexible linear telechelic chains with strongly attracting end-groups are studied under the influence of external shearing forces. Interconnection between structural and rheological properties of the steady-state system is discussed in detail, including the following aspects: shear-induced intra- and intermolecular structural changes, shear-induced gelation, shear thickening and thinning, thixotropic effect. We find that a critical factor in the shear behavior of self-associating polymers is the space distribution (topology) of chain "bridges" connecting micellar aggregates. Depending on the topology of the bridges, the system may exhibit shear thickening or shear thinning. Furthermore, the applied external force may cause transitions from continuous (space-filling) associative network, which spans the whole space, to fibrous textures-threadlike objects which align along the shear field. These structural reorganizations lead to dramatic changes in the shear dependent steady-state viscosity. (C) 1998 American Institute of Physics. [S0021-9606(98)51943-5].