Departamento de Materiales y Nanotecnología , Universidad Nacional de Colombia-Medellín , Medellín , 050034 , Colombia.
Institute for Molecular Engineering , University of Chicago , Chicago , Illinois 60637 , United States.
ACS Appl Mater Interfaces. 2018 Aug 15;10(32):27432-27443. doi: 10.1021/acsami.8b06611. Epub 2018 Aug 3.
The transition temperatures of nanoscale polymeric films are measured from a leveling experiment where a designed nanostructure is heated from below. Surface tension forces drive the relaxation of the polymeric features, allowing direct measurement of the critical temperature of collapse, T, and indirect measurement of the glass transition temperature, T. Small-angle X-ray scattering and atomic force microscopy are used to follow the leveling dynamics, whereas a mathematical model for the momentum balance is implemented to extract the viscosity of the polymer film as a function of temperature. Our methodology is illustrated in the context of films of poly(methyl methacrylate) that are patterned via nanoimprint lithography into dense gratings. We study how the glass transition temperature and the critical temperature of collapse vary as a function of the film size and the inclusion of the antiplasticizer, tris(2-chloropropyl) phosphate. The grating periods are varied consistently between 80 and 240 nm, whereas the antiplasticizer concentrations are 1, 3, 5, and 10 wt %. The solution of the momentum balance allows the detailed correlation between stresses, curvature, heating, and shear rates during leveling. We found that both temperatures, T and T, decrease as the film size decreases or as the concentration of the antiplasticizer increases. In addition, antiplasticizer concentrations between 3 and 5 wt % stabilize the size dependence of T. We show that the nature of the antiplasticizer is effectively to increase the low-temperature viscosity of the film. However, during leveling, the antiplasticized film sustains its curvature, thereby driving a sudden relaxation, once T is reached, and increasing the possibilities of defects.
从一个水平实验测量纳米级聚合物薄膜的转变温度，在该实验中，设计好的纳米结构从下方加热。表面张力驱动聚合物特征的松弛，允许直接测量崩溃的临界温度 T 和间接测量玻璃化转变温度 T。小角 X 射线散射和原子力显微镜用于跟踪水平动力学，而动量平衡的数学模型用于提取聚合物薄膜的粘度作为温度的函数。我们的方法以通过纳米压印光刻图案化为密集光栅的聚甲基丙烯酸甲酯薄膜为例进行说明。我们研究了玻璃化转变温度和崩溃临界温度如何随薄膜尺寸以及增塑剂三（2-氯丙基）磷酸酯的含量而变化。光栅周期在 80nm 到 240nm 之间一致变化，而增塑剂浓度为 1wt%、3wt%、5wt%和 10wt%。动量平衡的解允许在水平过程中详细关联应力、曲率、加热和剪切速率。我们发现，随着薄膜尺寸的减小或增塑剂浓度的增加，两种温度 T 和 T 都降低。此外，3wt%到 5wt%的增塑剂浓度稳定了 T 的尺寸依赖性。我们表明，增塑剂的性质有效地增加了薄膜的低温粘度。然而，在水平过程中，增塑薄膜保持其曲率，从而一旦达到 T 就会发生突然松弛，并增加缺陷的可能性。
