Impact of an Irreversibly Adsorbed Layer on Local Viscosity of Nanoconfined Polymer Melts

Abstract

We report the origin of the effect of nanoscale confinement on the local viscosity of entangled polystyrene (PS) films at temperatures far above the glass transition temperature. By using marker x-ray photon correlation spectroscopy with gold nanoparticles embedded in the PS films prepared on solid substrates, we have determined the local viscosity as a function of the distance from the polymer-substrate interface. The results show the impact of a very thin adsorbed layer (~7 nm in thickness) even without specific interactions of the polymer with the substrate, overcoming the effect of a surface mobile layer at the air-polymer interface and thereby resulting in a significant increase in the local viscosity as approaching the substrate interface.

Anomalous Viscosity Reduction and Hydrodynamic Interactions of Polymeric Nanocolloids in Polymers

“…Also, the values of δ are not too different from those extracted for polymers on a flat substrate. 15,16 Although, the actual effective viscosity experienced by the PGNPs in the film could have various factors (including intrinsic viscosity gradients in PS films 30 ), based on the above discussion, we postulate that it is largely due to the existence of an interface viscosity, η s (especially for 39 nm films), which is different from the bulk viscosity, η, as indicated in the schematic in Fig. 3(d).…”

“…We now use the well known temperature dependence of bulk viscosity of PS 38 to obtain the expected viscosity of the PNC films at each temperature for all the films. Although, existence of confinement effects on viscosity of thin polymer films has been widely discussed with a great deal of controversy 30,33 we have avoided usage of any such data or models. In any case we assume that any possible viscosity anomalies which exist in our films occur mostly at lower temperatures (near their T g ) and at the highest measured temperature at which our dynamics data exists, these anomalies would be minimal and it is, therefore, safe to assume bulk-like viscosity at the highest measured temperature.…”

Unexpected Molecular Weight Effect in Polymer Nanocomposites

“…Recently, Koga et al [20,29] explained the observed interfacial slowing down in supported thin films in terms of a bound loop layer (BLL) made of the loops of the adsorbed chains. According to them [20,29], the average height of the BLL provides a good estimate for the thickness of the DIL that experiences slower dynamics.…”

“…According to them [20,29], the average height of the BLL provides a good estimate for the thickness of the DIL that experiences slower dynamics. Considering the analogy between polymer thin films and PNCs [7,30], it is reasonable to anticipate a similar interfacial chain packing-dynamics relationship in PNCs [31,32].…”

A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores: Mixtures

“…Understanding and prediction of equilibrium and dynamic properties of fluids and their mixtures in nanopores are of considerable importance in various industrial processes and scientific fields such as separation of mixtures by porous materials, wetting, lubrication, and tribology. [1][2][3] A lot of methods have been used to represent the inhomogeneous behavior of confined fluids from experimental measurements, molecule simulations to theoretical models, and the classical density functional theory (DFT) in general provides reasonable description of inhomogeneous fluids with moderate computational cost. 4 A variety of DFT models have been developed to predict the properties of inhomogeneous simple atomic and complex fluids, and those based on Wertheim's first order thermodynamic perturbation theory (TPT1) are promising.…”