Dependence of viscoelastic flow functions on molecular structure for linear and branched polymers

Abstract

The flow properties were measured for concentrated n-butylbenzene solutions of well-characterized linear mono-and polydisperse polystyrene and polybutadiene, four-arm-star branched polystyrene and polybutadiene, and linear and four-arm-star branched random and block copolymers of styrene and butadiene. Concentrations varied from about 100 to 600 kg/m3. Polymer molecular weights varied from about 3 X 104 to 2.5 X 106. The viscosity and first and second normal stress difference functions of the shear rate, (i¡(y), Ni(y), N2(y)), and related steady-state shearing functions extending into the shear thinning region, and the unsteady shearing functions were determined in cone-plate shearing. The "zero" shear viscosity, 0, for linear polymers in the entanglement region was proportional to the entanglement density, E, to the 3.5 power. With the exception of the block copolymers, ij0 for the branched polymers was proportional to (gE)3S. The ratio N2/N1 was -0.29 for all linear-polymer data and -0.214 for all branched-polymer data with a standard deviation of less than 2%.

Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites

“…The magnitude of the second normal stress difference ( N 2 ) is usually much smaller than N 1 and it is always a negative value. According to Keentok et al and Ramachandran et al the relationship between N 1 and N 2 is given by . It must be taken into consideration that the measurement of the transient normal stress differences ( N 1 and N 2 ) is rather challenging due to the errors caused by the temperature variations and compliance of the instrument .…”

A purely elastic instability in Taylor–Couette flow

“…For example, in Lockett & Rivlin's analysis of the 'simple' fluid, there are nine such parameters. Such a complex constitutive equation may be required for describing melts or concentrated solutions of flexible polymer molecules (which we note are strongly shear thinning and usually have values of !P2/Yl in the range -0.10 to -0.30 (Keentok et al 1980;Ramachandran, Gao & Christiansen 1985)). However, dilute polymer solutions (i.e.…”

Comments on the Paper “Comparison of the Rheological Properties of Metallocene-Catalyzed and Conventional High-Density Polyethylenes”

“…(a, b) The fact that η 0 for entangled, linear, flexible polymers depends on molecular weight with an exponent of 3.4−3.6 has been well established, from theory − and from experimental data. − ,− In the case of conventional HDPE (linear ethylene homopolymer with less than 3−4 CH 3 /1000 C), the relationship η 0 = 3.4 × 10 -15 ( M̄ w ) 3.6 6,7 has been widely accepted for linear polymers with narrow molecular weight distributions; the same relationship holds (within experimental error limits) for linear ethylene polymers containing some short-chain branching (up to 20 CH 3 /1000 C) …”