Abstract
Thermally activated flow dynamics of polystyrene films supported by silicon is studied for a wide range of film thickness (h<sub>0</sub>) and molecular weights (M<sub>w</sub>). At low M<sub>w</sub>, the effective viscosity of the nanometer thin films is smaller than the bulk and decreases with decreasing h<sub>0</sub>. This is due to enhancement of the total shear flow by the augmented mobility at the free surface. As M<sub>w</sub> increases, with h<sub>0</sub> becoming smaller than the polymer radius of gyration (R<sub>g</sub>), the effective viscosity switches from being substrate-independent to substrate-dependent. We propose that interfacial slippage then dominates and leads to plug flow. The friction coefficient is found to increase with h<sub>0</sub> providing h<sub>0</sub>/R<sub>g</sub> < ∼1, demonstrating a surface-promoted confinement effect.
| Original language | English |
|---|---|
| Pages (from-to) | 5034-5039 |
| Number of pages | 6 |
| Journal | Macromolecules |
| Volume | 48 |
| Issue number | 14 |
| DOIs | |
| Publication status | Published - 28 Jul 2015 |
ASJC Scopus subject areas
- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry