Viscosity of PMMA on Silica: Epitome of Systems with Strong Polymer–Substrate Interactions

Abstract

We measured the viscosity of poly(methyl methacrylate) (PMMA) films supported by silica, where the carbonyl group on the side chains of the polymer interacts strongly with the hydroxyl groups of the surface. The result shows that the viscosity increases with decreasing film thickness at temperatures above 110 °C, but displays an opposite trend at lower temperatures. A three-layer model, consisting of a mobile top layer, a bulk-like middle layer and an immobile bottom layer was found to fit the data well. A detailed breakdown of the layer contributions to the total mobility unveils that the mobility gain brought about by the top layer is balanced by the mobility loss by the bottom layer at 110 °C. When the temperature is lowered or raised, the balance is offset, in favor, of the top and bottom layer, respectively.

A unifying framework to quantify the effects of substrate interactions, stiffness, and roughness on the dynamics of thin supported polymer films

“…The change in the T dependence of t * with varying film thickness leads to a crossing of t * for all thicknesses for T ≈ 0.5; this is reminiscent of the crossing point of the T dependence of viscosity for different film thicknesses observed experimentally. 49 However, there are important differences to consider. First, the temperature range of the experiments is relatively near to T g , while the crossover occurs at a significantly larger temperature in our simulations.…”

Viscosity and Surface-Promoted Slippage of Thin Polymer Films Supported by a Solid Substrate

“…Usually, the chain dynamics near the free (air) surface is faster than the bulk 6−11 but that near the substrate is slower. 12,13 By embracing analogous effects in a layer model, variations in the dynamic properties, including the glass transition temperature, T g , 10,14,15 and effective viscosity, η eff , 8,12,16 with the average polymer thickness, h 0 , were explained. At high molecular weights, M w , where the unperturbed radius of gyration, R g , exceeds ∼h 0 , de Gennes further proposed that the highmobility chain segments at the free surface can bring about mobility enhancement to the whole chain through chain connectivity.…”

Mechanical and viscoelastic properties of confined amorphous polymers

“…The strong interaction between PMMA and the pendant silanols of the substrate can lead to an increase in the average T g while overcoming the increased dynamics of the free surface . This interplay between the free surface and the substrate interactions impacts the thickness dependence of the viscosity of PMMA thin films determined from temporal evolution of capillary waves . The data can be well described in terms of a trilayer model consisting of a soft surface with increased dynamics, bulk‐like middle of the film and reduced dynamics of PMMA near the substrate .…”

“…This interplay between the free surface and the substrate interactions impacts the thickness dependence of the viscosity of PMMA thin films determined from temporal evolution of capillary waves . The data can be well described in terms of a trilayer model consisting of a soft surface with increased dynamics, bulk‐like middle of the film and reduced dynamics of PMMA near the substrate . The effect of confinement on the viscosity is temperature dependent with a compensation temperature of 110 °C; at higher temperatures, the effect of the substrate dominates and there is an effective increase in the viscosity, while at lower temperatures the viscosity in the thin films decreases .…”