Suppressed Chain Entanglement Induced by Thickness of Ultrathin Polystyrene Films
Fengliang Wang, Zhenwei Jiang, Xuanyu Lin, Cuiyun Zhang, Keiji Tanaka, Biao Zuo, Wei Zhang, Xinping Wang
Abstract
The thickness effect on the relaxation behavior and chain entanglements was investigated for thin polystyrene films. By following the time evolution of the wetting ridge at the surface induced by a droplet of ionic liquid, the characteristic time (τ*) at which the ridge height started to change was obtained. Here, we demonstrated experimentally that the characteristic time was associated with the disentanglement time τd, τ* ∼ τd ∼ Mw3.4/Me1.4, where Me denotes the entanglement molecular weight. The critical thickness (hc) at which τ* started to decrease was approximately 3.3Rg. That is, the Me increased, or the interchain entanglement density decreased, as the film became thinner than the hc. This might be explained in terms of the conformational change from “spherical” to “ellipsoidal”, leading to a reduction in the pervaded volume (Vp) of chains in the ultrathin films.