Anomalous bulk viscosity of polymer-nanocomposite melts

Abstract

Nanoparticles dispersed in polymer melts have recently been shown to decrease the bulk viscosity. This contradicts expectations based on Einstein's well-known theory for effective viscosity of dilute, random dispersions of rigid spheres in Newtonian fluids. In this paper, we examine a continuum hydrodynamic model where a layer of polymer at the nanoparticle-polymer interface has a different viscosity and density than the bulk polymer. When the layer thickness is greater than the nanoparticle radius, and the layer viscosity is lower than that of the bulk polymer, the intrinsic viscosity is comparable to the unexpectedly large, negative values reported experimentally by Mackay and coworkers. Accordingly, our continuum hydrodynamic model attributes a bulk viscosity reduction to a lower melt viscosity at the nanoparticle-polymer interface. Such a reduction has been ascribed to the Rouse dynamics of polymer chains at the nanoparticle-polymer interface. Fitting the theory to experimental data reveals a simple correlation between the reduced viscosity layer thickness, polymer chain size, entanglement tube diameter, and nanoparticle size and concentration. Our calculations support the arguments of Mackay and coworkers that nanoparticle inclusions significantly influence the polymer chain conformation in melts, even when the inclusion volume fraction is very small.

Polymer nanocomposites having a high filler content: synthesis, structures, properties, and applications

“…Viscosity of the polymer solution is usually increased to form solid-like viscoelastic behaviour by incorporation of nanofiller (e.g., CNT, graphene) which is undesirable for solution mixing 259 . However, anomalous behaviour has recently been observed 153,154,[260][261][262][263] . Slip between silica nanospheres and polymer occurred depend on particles size and polymer chain size, decreasing the bulk viscosity of polymer nanocomposite 261 .…”

Anomalous Viscosity Reduction and Hydrodynamic Interactions of Polymeric Nanocolloids in Polymers

“…39,43,49 As mentioned earlier, the WH model 49 has delineated the role of morphology and hydrodynamic slip at the nanoparticle-polymer interface in determining the effective viscosity of PNC melts. We believe that the de-wetting nature of our PGNP-PS interface and the low penetrability 53 by the matrix PS chains of the grafted chains makes the existence of large interface slip and an effective reduced viscosity at the nanoparticle-polymer interface highly probable.…”

“…In fact the WH model 49 suggests that slip becomes relevant in determining the intrinsic viscosity provided the width of the PGNPpolymer interface is smaller. This is actually quite relevant for our system of grafted PST and matrix PS chain molecular weight ratios for which this width is estimated 53 We would like to state here that although, the dimensions of our system (PGNP diameter ∼ 6 nm and PS tube diameter ∼ 8-9 nm) also satisfies the conditions for applicability of the DW model for non-Einstein like viscosity in our PNC films, the relatively weak temperature dependence of entanglement tube diameter suggests that the DW models or its analogues cannot explain the observed temperature dependent viscosity anomaly effects.…”

Universal Viscosity Behavior of Polymer Nanocomposites

“…[1][2][3] However, for nanosized fillers, can be reduced or increased relative to the pure polymer. [4][5][6][7][8][9][10][11][12] While there have been extensive simulations of nanocomposites, [13][14][15][16][17][18] most have focused on the importance of polymer-NP interactions on flow behavior. 9,19 The complicated, and poorly understood, dependence of on NP size, chain size, and polymer-NP interactions, are the issues we study here.…”