Institute of Physics, Albert Ludwig University of Freiburg, 79104 Freiburg, Germany.
Phys Rev Lett. 2016 Feb 26;116(8):088301. doi: 10.1103/PhysRevLett.116.088301. Epub 2016 Feb 23.
We compare the high velocity dewetting behavior, at elevated temperatures, of atactic polystyrene (aPS) and isotactic polystyrene (iPS) films, with the zero shear bulk viscosity (η_{bulk}) of aPS being approximately ten times larger than iPS. As expected, for aPS the apparent viscosity of the films (η_{f}) derived from high-shear dewetting is less than η_{bulk}, displaying a shear thinning behavior. Surprisingly, for iPS films, η_{f} is always larger than η_{bulk}, even at about 50 °C above the melting point, with η_{f}/η_{bulk} following an Arrhenius behavior. The corresponding activation energy of ∼160±10 kJ/mol for iPS films suggests a cooperative motion of segments which are aligned and agglomerated by fast dewetting.
我们比较了无规聚苯乙烯（aPS）和等规聚苯乙烯（iPS）薄膜在高温下的高速去湿行为，其中 aPS 的零剪切体粘度（η_{bulk}）大约是 iPS 的十倍。正如预期的那样，对于 aPS，从高剪切去湿得到的薄膜表观粘度（η_{f}）小于 η_{bulk}，表现出剪切变稀行为。令人惊讶的是，对于 iPS 薄膜，即使在熔点以上约 50°C 的温度下，η_{f}也总是大于 η_{bulk}，并且 η_{f}/η_{bulk}遵循阿累尼乌斯行为。对于 iPS 薄膜，对应的约 160±10 kJ/mol 的活化能表明，通过快速去湿而对齐和聚集的链段的协同运动。
