# Stable polydisperse free-standing porous films made by mechanical deformation

## TL;DR

Researchers used simulations to show that stretching and cooling a mix of long and short polymer chains creates stable porous films.

## Contribution

The study demonstrates that polydisperse polymer films can be made stable using mechanical deformation and cooling.

## Key findings

- Long polymer chains stabilize the porous structure by spanning multiple pores.
- Short chains aggregate inside the polymer matrix and avoid surfaces during cooling.
- The process works similarly for polydisperse films as it does for monodisperse films.

## Abstract

Using molecular dynamics simulations, we show that the methodology of making thin stable nanoporous monodisperse films by biaxial mechanical expansion and subsequent cooling into the glassy state, also works for polydisperse films. To test this, a bidisperse polymer system of an equal number of very long (≈72 entanglements) and short (≤4 entanglements) chains with a polydispersity index of 1.80 is considered. The void formation and the development of the local morphology upon expansion, relaxation, and cooling are investigated. As for the monodisperse case, long chains in thin porous polydisperse films extend over several pores, stabilizing the whole morphology. The short chains do not fill up the pores but tend to aggregate inside the polymer matrix and to avoid surface areas and reduce conformational constraints imposed by the surrounding, a scenario very similar to strain-induced segregation between the strained long and relaxed short chains.

Nanoporous polymer film made by biaxial expansion of a polydisperse polymer melt. The film is stabilized by long polymer chains extending over several pores. Short chains aggregate inside the bridges between pores.