Fiber formation from the melting of free-standing polystyrene, ultra-thin films: A technique for the investigation of thin film dynamics, confinement effects and fiber-based sensing.

摘要

Free-standing ultra-thin films and micro to nanoscale fibers offer a unique geometry in which to study the dynamics of thin film stability and polymer chain dynamics. By melting these films and investigating the subsequent processes of hole formation and growth, and fiber thinning and breakup, many interesting phenomena can be explored, including the nucleation of holes, shear-thinning during hole formation, finite-extensibility of capillary thinning viscoelastic fibers, and confinement effects on entanglement of polymer chains. Free-standing films in the melt are unstable and rupture due to instabilities. The mechanism of membrane failure and hole nucleation is modeled using an energy barrier approach which is shown to capture the dependence of hole nucleation on thickness. The formed holes grow exponentially and are found to grow under a shear thinning, nonlinear viscoelastic, high shear strain regime. These holes impinge upon each other to form suspended fibers. The fibers thin according to a model for the elasto-capillary thinning of the suspended viscoelastic fluid filaments. Monitoring fiber thinning allows for the acquisition of rheological properties as well as the transient, apparent extensional viscosity giving insight into strain hardening and eventual steady-state extensional viscosity. The decay and breakup of these fibers and their interconnected branched structure indicates the effects of confinement on chain entanglement in ultra-thin films. A transition below a critical film thickness, comparable to the dimensions of a polymer chain, shows drastically reduced interchain entanglements and a remarkably faster breakup of suspended fibers. The processes of fiber formation from the melting of ultra-thin films are explored in high detail and produce a new technique for the investigation of rheological and material properties, confinement effects, and the dynamics of thin films and polymer chains.