Capillary instability in nanoimprinted polymer films

Abstract

Capillary forces play an active role in defining the equilibrium structure of nanoscale patterns. This effect can be especially pronounced in soft materials such as polymers near or above their glass transition temperature (T g ) where material flow is possible. In these situations, the effect of surface tension can produce varied and complex capillary instabilities, even in relatively simple geometries such as parallel-line-space grating patterns. Here we investigate a novel capillary instability that arises upon thermal annealing of nanoimprinted polystyrene line-space gratings with an underlying residual layer. This novel instability is characterized by the development of lateral undulations of the lines, culminating in the localized coalescence of adjacent imprinted lines. An exact analytic model of this undulatory instability is not tractable, but we introduce a simple physical model for this lateral instability based on the driving force to reduce the surface energy, as in the well-known RayleighPlateau instability, which is likewise surface-energy driven. Good agreement is obtained between this simplified model and our observations. Our insights into the nature of this instability have implications for controlling the thermal stability of nanoscale patterns fabricated by nanoimprint lithography or other lithography techniques.

Inadvertent subclavian artery catheter placement complicated by stroke: Endovascular management and review

“…Lateral undulations were observed in all molecular weight samples used (including the 19.3 kg/mol PS) with a relatively high FS loading (3.2 and 16%) for the 424 nm pitch patterns. We find that as noted previously41 this decay mode is characterized by formation of a periodic undulation of the imprinted lines having μm scale wavelength, where neighboring lines undulate nearly out‐of‐phase in a quasi‐periodic fashion. As the separation between neighboring lines decreases, there is local coalescence or merging of the lines [Fig.…”

“…1(e)]. This lateral instability appears to be identical to the one we have recently observed in pure PS patterns with high molecular weight and relatively high imprint temperature 41. Lateral undulations were observed in all molecular weight samples used (including the 19.3 kg/mol PS) with a relatively high FS loading (3.2 and 16%) for the 424 nm pitch patterns.…”

“…The phase relation between undulations on neighboring lines appears to be nearly random. In our previous article we noted that both in‐phase and out‐of‐phase varicose undulations of this type can lead to surface area reduction and are possible modes for decay 41. These model surfaces are shown for comparison in Figure 3(d).…”

Pattern-Directed Phase Separation of Polymer-Grafted Nanoparticles in a Homopolymer Matrix

“…6a), which is ascribed to capillary instability associated with minimization of interfacial contact area between AuPS domains and PMMA matrix. 47,48 …”

Viscoelastic properties measurements of thin polymer films from reflow of nanoimprinted patterns

“…At temperature above T g , the film flows under surface tension 15,17,18 and reaches a steady state when the surface energy of the free interface is minimum; in other words when the film is completely flat. During the reflow process, a) Electronic mail: etienne.rognin@cea.fr high frequency features tend to disappear faster than general shapes, resulting in the smoothing of the patterns, which has been observed in numerous experimental works.…”