期刊
MACROMOLECULES
卷 46, 期 8, 页码 3190-3197出版社
AMER CHEMICAL SOC
DOI: 10.1021/ma3022986
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资金
- National Science Foundation [CBET-0730692, CBET-0731319]
- DOE's Office of Science [DE-AC02-06-CH11357]
- DURIP program [W911NF-09-1-0122]
The surface fluctuation dynamics of melt films of densely branched comb polystyrene of thickness greater than 55 nm and at temperatures 23-58 degrees C above the bulk T-g can be rationalized using the hydrodynamic continuum theory (HCT) known to describe melts of unentangled linear and cyclic chains. Film viscosities (eta(XPCS)) inferred from fits of the HCT to X-ray photon correlation spectroscopy (XPCS) data are the same as those measured in hulk rheometry (eta(bulk)) for three combs. For the comb most like a star polymer and the comb closest to showing bulk entanglement behavior, eta(XPCS) > eta(bulk). These discrepancies are much smaller than those seen for less densely branched polystyrenes. We conjecture that the smaller magnitude of eta(XPCS) - eta(bulk) for the densely grafted combs is due to a lack of interpenetration of the side chains when branching is most dense. Both T-g,T-bulk and the specific chain architecture play key roles in determining the surface fluctuations.
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