Temperature Dependence of the Slip Length in Polymer Melts at Attractive Surfaces

Abstract

Using Couette and Poiseuille flows, we extract the temperature dependence of the slip length, delta, from molecular dynamics simulations of a coarse-grained polymer model in contact with an attractive surface. delta is dictated by the ratio of bulk viscosity and surface mobility. At weakly attractive surfaces, lubrication layers form; delta is large and increases upon cooling. Close to the glass transition temperature Tg, very large slip lengths are observed. At a more attractive surface, a sticky surface layer is built up, giving rise to small slip lengths. Upon cooling, delta decreases at high temperatures, passes through a minimum, and grows for T-->Tg. At strongly attractive surfaces, the Navier-slip condition fails to describe Couette and Poiseuille flows simultaneously. The simulations are corroborated by a schematic, two-layer model suggesting that the observations do not depend on details of the computational model.

Anomalous Viscosity Reduction and Hydrodynamic Interactions of Polymeric Nanocolloids in Polymers

“…We argue that this is very relevant for our system i.e. the observed α value of 2 is clearly indicative of large slip and the reduction of this value with increasing temperature T corroborates with the anticipated reduction of slip with increasing temperature 47,48 and also is consistent with the analysis and interpretation we provided to explain the large reduction in viscosity ratios earlier in Fig. 3.…”

“…The extent of slip is dependent on the penetration length of the matrix chains into the flat brush region 48,55 (in our case the PGNP particles). 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.…”

“…15,48 For the corresponding case of polymer near nanoparticle the role of the nanoparticle-polymer interface has been highlighted in the context of dispersion 22,24,28,54 or thermo-mechanical properties of PNCs.…”

“…Figure 3 (c) shows the evolution of δ with temperature, which is similar to the variation predicted by Servantie et.al. 48 Although there might be uncertainties in the actual magnitudes of extracted δ due to the approximations involved, including that in the microscopic slip length, δ s , the temperature and film thickness dependence should be reliable. Also, the values of δ are not too different from those extracted for polymers on a flat substrate.…”

Crossover to surface flow in supercooled unentangled polymer films

“…Generic properties independent of the details in the molecular structure are most efficiently simulated by using classical coarse-grained models in which groups of closely bounded atoms are represented by point particles. Within this framework, thin films that are supported by a substrate [12][13][14][15], free standing [12,16,17], or sandwiched between impenetrable walls [18][19][20][21][22] were studied. Experimentally observed deviations of T g from the bulk value were generally reproduced.…”