Sharp J S, Forrest J A
Department of Physics, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1.
Phys Rev Lett. 2003 Dec 5;91(23):235701. doi: 10.1103/PhysRevLett.91.235701. Epub 2003 Dec 3.
The effect of free surfaces on the glass transition temperature (T(g)) of thin polystyrene films was studied. Measurements were performed on films (8 nm<h<290 nm) with one free surface and on films capped with a 5 nm thick metal layer (no free surfaces). Potential problems with evaporative deposition were eliminated by studying samples made of two supported films placed with their free surfaces in contact and annealed. Uncapped films displayed reduced T(g) values for h less, similar 40 nm while all "properly" capped films exhibited a T(g) value the same as that of the bulk polymer (370+/-1 K). When the free surface was restored, the measured T(g) values the same as those of uncapped films of the same thickness. These results show that free surfaces are crucial for observing T(g) reductions in thin polymer films and address the role of the sample preparation history.
研究了自由表面对聚苯乙烯薄膜玻璃化转变温度（T(g)）的影响。对具有一个自由表面的薄膜（8纳米＜h＜290纳米）以及覆盖有5纳米厚金属层（无自由表面）的薄膜进行了测量。通过研究由两个自由表面相互接触放置并退火的支撑薄膜制成的样品，消除了蒸发沉积可能存在的问题。对于厚度小于约40纳米的未覆盖薄膜，其T(g)值降低，而所有“适当”覆盖的薄膜表现出与本体聚合物相同的T(g)值（370±1K）。当恢复自由表面时，测得的T(g)值与相同厚度的未覆盖薄膜相同。这些结果表明，自由表面对于观察聚合物薄膜中T(g)的降低至关重要，并说明了样品制备历史的作用。
