Rheology of hyperbranched polymer melts undergoing planar Couette flow

Abstract

The melt rheology of four hyperbranched polymer structures with different molecular weights has been studied using nonequilibrium molecular dynamics (NEMD). Systems were simulated over a wide range of strain rates to capture the crossover behavior from Newtonian to non-Newtonian regimes. Rheological properties including shear viscosity and first and second normal stress coefficients were computed and the transition to shear thinning was observed at different strain rates for hyperbranched polymers of different sizes. The results were consistent with previous findings from NEMD simulation of linear and dendritic polymers. Flow birefringence was characterized by taking into account both form and intrinsic birefringences, which result from molecular and bond alignment, respectively. The stress optical rule was tested and shown to be valid only in the Newtonian regime and violated in the strong flow regime where the rule does not take into account flow-induced changes of the microstructure.

Entanglement Transition in Hyperbranched Polyether‐Polyols

“…Moreover, simulation for hyperbranched polymers with nonequilibrium molecular dynamics (NEMD) demonstrated a single a-value of approximately 0.65 for both hyperbranched polymers and dendrimers and therefore the absence of entanglements, since the scaling relation does not split into two different regimes. [15] However, within the scope of recent studies, some initial results suggesting entanglement in extremely high molecular weight hyperbranched polymers have been found. By considering a wide range of molecular weights, complex patterns of scaling relations between zero shear viscosity and molar mass have been observed.…”

Non-Newtonian behavior and molecular structure of Cooee bitumen under shear flow: A non-equilibrium molecular dynamics study

“…The absolute value of the second normal stress coefficient Ψ 2 decreases with increasing shear rate, which is also a signature of the non-Newtonian regime. The decrease of the two normal stress coefficients in the non-Newtonian regime can be fitted to a power law [25]:…”

“…This algorithm is able to reproduce a shear Couette flow, even far from equilibrium [23] and provide the value of the shear rate dependent viscosity. The SLLOD algorithm has been used to simulate shear flow of complex systems such as hyperbranched polymers [25], associating polymer solutions [26] and ionic liquids [27]. In this paper, we applied it to Cooee bitumen [28], which is a four-component bitumen model describing a bitumen with generic mechanical properties [17] and molecular structure [18 and 29].…”

Describing the Structure of a Randomly Hyperbranched Polymer

“…[27] In contrast to the extensive research into dendrimers, hyperbranched polymers have received much less attention. Richards et al [28] and Buzza [29] studied the properties of hyperbranched polymer using information from theoretical molecular weight distributions, and these have also been several simulation studies of relatively low-molecular-weight hyperbranched polymers under various conditions, [30][31][32][33][34][35][36] which have been subsequently extended to higher degrees of polymerization. [37,38] More recently, a model called random branching theory was developed to describe randomly hyperbranched polymers.…”