Shear rheology and structural properties of chemically identical dendrimer-linear polymer blends through molecular dynamics simulations

Abstract

We present nonequilibrium molecular dynamics (NEMD) simulation results for the miscibility, structural properties, and melt rheological behavior of polymeric blends under shear flow. The polymeric blends consist of chemically identical linear polymer chains (187 monomers per chain) and dendrimer polymers of generations g = 1-4. The number fraction x of the dendrimer species is varied (4%, 8%, and 12%) in the blend melt. The miscibility of blend species is measured, using the pair distribution functions gDL, gLL, and gDD. All the studied systems form miscible blend melts under the conditions investigated. We also study the effect of shear rate γ̇ and dendrimer generation on inter-penetration between blend species for different blend systems. The results reveal that shear flow increases the interpenetration of linear chains toward the core of the dendrimers. We also calculate the shear-rate dependent radius of gyration and ratios of the eigenvalues of the gyration tensor to study the shear-induced deformation of the molecules in the blend. Melt rheological properties including the shear viscosity and first and second normal stress coefficients obtained from NEMD simulations at constant pressure are found to fall into the range between those of pure dendrimer and pure linear polymer melts.

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

“…This is important in tribology since PEF occurs in the entrance region of high pressure, elastohydrodynamic contacts [95]. PEF simulations have been widely used to study polymers flow [96,97] but more rarely for lubricant-sized molecules. Baig et al [98] studied the rheological and structural properties of linear liquid n-alkanes (C 10 , C 12 , C 20 ) using NEMD simulations under PEF.…”

A molecular dynamics investigation of the planar elongational rheology of chemically identical dendrimer-linear polymer blends

“…[34][35][36][37][38][39] A crucial question arises when blending linear chain polymers with these tree-like molecules, and that is under which conditions these species will form a miscible blend. This issue has been partially addressed in our previous paper, 40 in which we showed that since our model dendrimers and linear polymers had an identical chemical nature, the molecular size ratio between the linear and dendrimer molecules is the main parameter influencing their miscibility. All of our blend systems formed miscible blends.…”

“…In this way, the penetration of the beads belonging to linear molecules toward the interior of dendrimer molecules is analysed. 40 Fig. 4 compares the g c,DL function for the blend systems 12D187B, 8D187B, and 4D187B atε = 2 × 10 −4 to display the dependence of interpenetration on the dendrimer concentration at fixed dendrimer molar mass.…”

“…Therefore, an increased number of dendrimer species in the blend leads to an increase in the fractional free volume of the system, 48 which can facilitate motion of the linear chains in the blend melt, and consequently leads to more interpenetration. 40 FIG. 5.…”

“…We also showed that dendrimers, due to their globular constrained shape and unique inter-connected structure, show particle-like behaviour along with their macromolecular characteristics. 40 Therefore, our blend systems are similar to a specific class of nanocomposites where nanoparticles and polymer chains have the same chemical nature. Mackay et al studied the reduction in viscosity, 41 miscibility, 42 and structural changes of linear polystyrene (PS) molecules 43 in the presence of spherical cross-linked PS and dendritic polyethylene (PE) nanoparticles.…”