Linear viscoelasticity of polystyrene solution having a wide molar mass distribution around the coil overlap concentration

Abstract

Linear viscoelastic behavior for solutions of polystyrene (PS) having broad molar mass distribution (MMD) in tricresyl phosphate (TCP), which is a good solvent, was investigated at concentrations, c, around the coil-overlappingconcentration, c*. GPC measurement indicated that molar mass distribution of sample was close to most probable distribution. Below c*, the viscoelastic behavior was described well with the Rouse-Zimm (RZ) theory if considered molar mass distribution. On the other hand, at concentrations around the c*, the viscoelastic behavior was not described by the RZ mode alone and the additional long-time (LT) modes were needed, similarly to the case of monodispersed molar mass distribution system. This implies that the LT modes are originated by the inter-molecular interaction. Compared with the monodispersed system, magnitude of the LT modes showed the same c dependence, being proportional to c2 while the relaxation time of the LT mode showed a different c dependence. Owing to the broad MMD and the LT term, the viscoelastic spectra have the broad terminal flow relaxation time distribution but still can be apparently fit with the Rouse-Zimm (RZ) theory, resulting that the apparent molar mass, Mappw, is higher molar mass than the real molar mass depending at concentrations of c > c*. At c / c* = 2.9, Mappw was estimated at 4.1 times larger than the true molar mass. By considering the LT terms, the molar mass can be estimated by fitting with the Rouse- Zimm (RZ) term. © 2013 The Society of Rheology, Japan.