Ding Yifu, Ro Hyun Wook, Germer Thomas A, Douglas Jack F, Okerberg Brian C, Karim Alamgir, Soles Christopher L
Polymers Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, Maryland 20899-8541, USA.
ACS Nano. 2007 Sep;1(2):84-92. doi: 10.1021/nn700014p.
We study the decay of imprinted polystyrene (PS) patterns under thermal annealing using light diffraction. The first-order diffraction intensity from the imprinted gratings was measured as a function of annealing time. A local intensity maximum is observed as a function of annealing time. This "abnormal" intensity variation can be qualitatively understood, using rigorous coupled wave approximation calculations, as a characteristic diffraction from patterns with specific shape/height. We demonstrate that this diffraction anomaly can be used to characterize the temperature dependence of the pattern decay rate. The activation energies of the pattern decay are found to be similar to those of the segmental and chain relaxations. Comparisons between PS samples of different molecular mass reveal that the patterns decay through different mechanisms. For unentangled PS, the decay of the imprinted pattern follows the surface-tension-driven viscous flow, with a viscosity similar to the steady-state viscosity. However, for highly entangled PS, large residual stresses introduced from the imprinting process cause the pattern to decay much faster than expected from surface-tension-driven viscous flow.
我们利用光衍射研究了热退火条件下印迹聚苯乙烯（PS）图案的衰减。测量了印迹光栅的一阶衍射强度随退火时间的变化。观察到一阶衍射强度随退火时间出现局部最大值。利用严格耦合波近似计算，这种“异常”的强度变化可以定性地理解为具有特定形状/高度图案的特征衍射。我们证明这种衍射异常可用于表征图案衰减速率的温度依赖性。发现图案衰减的活化能与链段和链松弛的活化能相似。不同分子量的PS样品之间的比较表明，图案通过不同的机制衰减。对于未缠结的PS，印迹图案的衰减遵循表面张力驱动的粘性流动，其粘度类似于稳态粘度。然而，对于高度缠结的PS，印迹过程中引入的大残余应力导致图案衰减得比表面张力驱动的粘性流动预期的要快得多。
