Anomalous Surface Relaxations of Branched-Polymer Melts

The dynamics of thermally stimulated surface fluctuations of 100 nm thick films of long-branched polymers are measured for the first time. In contrast to comparable films of linear or cyclic chains that show no change in viscosity upon confinement, films of 6-pom, 6-star, and 6-end end-branched stars show viscosities, inferred from x-ray photon correlation spectroscopy, as much as 100 times higher than in the bulk. This difference varies in magnitude with chain architecture. Branching has a profound effect on confinement, even for these unentangled chains.

Figure 1

Schematics and abbreviated names of the architectures of the linear, six arm star-branched, six arm pom-pom, and six arm, end-branched star polystyrenes.

Figure 2

Comparison of viscosities obtained from XPCS data (open symbols) with viscosities from bulk rheology (filled symbols) as a function of $T-T_{g,\mathrm{bulk}}$ for branched architectures as marked.

Figure 3

Angell plot showing zero shear viscosities of branched chains and linear analog as a function of $T_{g,\mathrm{bulk}}/T$ shown with values of ${\eta }_{\mathrm{XPCS}}$.