AFM characterization of annealed nanoimprinted patterns applied to rheological properties measurement of thin polymer films with shear rate control

In several applications where flows at the nanoscale play an important role, such as nanoimprint lithography or nanopatterns reflow, in situ rheological properties measurements are required. We developed a fast and cost-effective method to measure the rheological properties of a thin polymer film from the reflow of purposely designed nanoimprinted patterns. The novelty of our approach is based on the accurate spatial determination of the film surface with use of atomic force microscopy (AFM), rather than on its temporal evolution. Here, a particular attention is given to the verification of the linear rheological response of the material. Indeed, if the shear rate in the flowing film reaches a critical value, non-linear behaviors such as shear thinning can be expected. Using the framework of capillary wave theory, we show that it is possible to analytically assess the shear rate at any point within the film, only knowing the position of the free interface (measured by AFM) and the zero-shear viscosity. We show that in our experimental setup, the shear rate never reaches critical values and we confirm the linear rheology hypothesis.

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► Rheological properties measurement of a thin polymer.
► Non-linear behaviors such as shear thinning can be expected.
► Shear rate at any point within the film can be assessed.
► Linear behavior (such as Newtonian) can be checked.