Thomas Katherine R, Chenneviere Alexis, Reiter Günter, Steiner Ullrich
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Feb;83(2 Pt 1):021804. doi: 10.1103/PhysRevE.83.021804. Epub 2011 Feb 28.
The rheological behavior of 100-nm-thick polystyrene films cast from various solvents was examined using an electric field to weakly perturb the free surface of the polymer melt. The effective viscosity and residual stresses of the as-spun films are seen to strongly depend on the properties of the casting solvent and the solvent quality. Both effects are explained in terms of the coil dimension at the solvent-polymer composition at which the film vitrifies. The more compact chains in a near-Θ-solvent are less entangled and less deformed when quenched to the dry melt compared to the more swollen chains in an athermal solution. Despite chain conformations that are further from equilibrium for the Θ-solvent cast chains, these films have reduced stored stresses compared to the chains cast in films from athermal solvents. A more detailed analysis of the data suggests that the formation of a surface-near region with more strongly deformed chains during spin coating. Since thermal equilibration of spin-cast high-molecular-weight films is unpractical, solvent vapor annealing was used to equilibrate films on timescale of a few hours.
利用电场对聚合物熔体的自由表面进行微弱扰动，研究了由各种溶剂浇铸而成的100纳米厚聚苯乙烯薄膜的流变行为。可以看出，初纺薄膜的有效粘度和残余应力强烈依赖于浇铸溶剂的性质和溶剂质量。这两种效应都可以根据薄膜玻璃化时溶剂 - 聚合物组合物中的线团尺寸来解释。与在无热溶液中更膨胀的链相比，在近θ溶剂中更紧密的链在淬火至干熔体时缠结较少且变形较小。尽管对于θ溶剂浇铸的链，链构象离平衡更远，但与从无热溶剂浇铸在薄膜中的链相比，这些薄膜的储存应力降低。对数据的更详细分析表明，在旋涂过程中形成了一个靠近表面的区域，其中链的变形更强。由于对旋铸的高分子量薄膜进行热平衡是不实际的，因此使用溶剂蒸汽退火在几小时的时间尺度上使薄膜平衡。
