Large-Scale Heterogeneities in Entangled Polymer Solutions. Light-Scattering Study on Polystyrene in Toluene

Abstract

Static and dynamic low-angle light-scattering experiments carried out on semidilute and moderately concentrated solutions of polystyrene in toluene provide evidence for the existence of heterogeneities in the entanglement network with correlation lengths of several hundred nanometers. The slow mode showing up in the correlograms in addition to the gel mode reflects the diffusive motion of these chain associations. The tendency to form associations increases with the solute concentration and with decreasing temperature. The observations indicate that the reptation time does not represent the longest relaxation time in the system; a complete reorganization of the entanglement network requires a much longer period.

Comparison of the gelation dynamics for polystyrenes prepared by conventional and living radical polymerizations: a time-resolved dynamic light scattering study

“…For semi-dilute and concentrated polymer solutions, two relaxation modes [27][28][29] corresponding to mutual diffusion and viscoelastic relaxation [30][31][32] or large-scale heterogeneities [33] have been reported in the literature. The fast mode was also often referred to as cooperative or collective diffusion.…”

“…As the concentration becomes higher, ICF exhibits two modes, suggesting the evolution of PSt chains and existence of larger length scale fluctuations. The origin of these modes for polymeric systems has been discussed in a large number of references [27][28][29][30][31][32][33]. When we enter the semi-dilute regime, where chains overlap with each other, the interpretation of the dynamics becomes complicated by the complex forms of osmotic pressure, friction coefficient, z, and the diffusion equation characterized by the coupling between diffusion and stress.…”

Structure and dynamics of a pentablock copolymer of polystyrene-polybutadiene in a butadiene-selective solvent

“…The origin of this mode is not fully understood, it may reflect the heterogeneity inherent in a block copolymer due to the existence of two or more monomers; or it may represent an association between chains. Slow modes, called cluster-modes have been observed in the long-range density correlations of homopolymer and copolymer melts and low molecular weight glass formers [29][30][31][32]. In physical gels such as those used here microsyneresis is commonly observed and would give rise to long-length scale inhomogeneities.…”

Dynamics of solutions of triblock copolymers in a selective solvent: Effect of varying copolymer concentration

“…46 -49 Recently, large-scale heterogeneities with correlation lengths of several hundred nanometer were observed in semidilute and moderately concentrated polystyrene solutions in toluene. 50 The tendency to form clusters increases with increasing solute concentration and with decreasing temperature. Similar inhomogeneities were also observed in SAXS measurements on moderately concentrated polystyrene solutions in dioctylphthalate 51 and in cyclohexane.…”

“…The phenomenon is probably unrelated to the block copolymer nature of the chains, instead it may be related to the entangled transient network in concentrated solutions. 50 In the particular case of PS-PEB-PS triblock copolymer solutions in heptane, the slow mode may arise due to the presence of aggregates of insoluble homopolymer impurities (polystyrene), which come from the copolymer preparation. This interpretation can be supported by the QELSS data shown in Figure 7, where we compare normalized intensity correlation functions, g (2) (t), for solutions of fractionated and nonfractionated samples, both with c ϭ 6.9 % in n-heptane.…”