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[摘要]：A study of the confinement effects on chain entanglements in free-standing ultrathin (<100 nm) polymer films is presented. Chain entanglements are probed by determining the lifetime and breakup time scale of a branched network of suspended fibers formed from the annealing of these films. Films of polystyrene (between SO and 100 nm) cast via flow coating are suspended atop lithographically patterned arrays of pillars. The films are then annealed above the glass transition temperature, where holes are randomly formed. The holes expand exponentially due to capillary forces and impinge upon each other to form a suspended, branched network of fibers. The thinning of fibers as well as the lifetime and breakup of this fiber network is observed via optical microscopy. A model for the viscoelastic-capillary thinning of fibers can be applied to determine a time scale for the breakup of individual samples. The decay of this time scale, below a critical parent film thickness, shows a transition between interchain and self-entanglements when crossing into a confined regime, illustrating a significantly decreased interchain entanglement density and breakdown in the entangled network of the polymer melt. This analysis of confinement effects on chain entanglement extends the understanding of ongoing studies into suspended fiber formation from the melting of freestanding polymer thin films. A better knowledge of chain entanglements in confined systems will make future fabrication of nanoscale suspended fibers, new architectures, and subsequent devices more controlled and accessible. |
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