Free Standing Dry and Stable Nanoporous Polymer Films Made through Mechanical Deformation

Abstract

A new straight forward approach to create nanoporous polymer membranes with well defined average pore diameters is presented. The method is based on fast mechanical deformation of highly entangled polymer films at high temperatures and a subsequent quench far below the glass transition temperature Tg. The process is first designed generally by simulation and then verified for the example of polystyrene films. The methodology does not need any chemical processing, supporting substrate, or self assembly process and is solely based on polymer inherent entanglement effects. Pore diameters are of the order of ten polymer reptation tube diameters. The resulting membranes are stable over months at ambient conditions and display remarkable elastic properties.

Entanglement-Stabilized Nanoporous Polymer Films Made by Mechanical Deformation

“…The Porod law S ⊥ (q ⊥ ) ∼ q ⊥ −4 is also shown by a straight line for comparison. polymer interfaces (see Figure S8, Supporting Information), which is qualitatively in agreement with experimental findings, 25 and a crossover to S ∥ (q ∥ ) ∼ q ∥ −2 with the increase of q ∥ , when the individual chain structure becomes relevant. The latter is only clearly seen for fast expanded films.…”

“… 22 , 31 From ideally sharp and smooth (flat) pore surfaces, one expects (Porod’s law) S ∥ ( q ) ∼ q ∥ –4 in the intermediate range of q ∥ . 54 For slowly expanded films at 4.0, we observe a tendency toward such smooth void–polymer interfaces (see Figure S8 , Supporting Information), which is qualitatively in agreement with experimental findings, 25 and a crossover to S ∥ ( q ∥ ) ∼ q ∥ –2 with the increase of q ∥ , when the individual chain structure becomes relevant. The latter is only clearly seen for fast expanded films.…”

“…However, our finding that even at T = 1.0ϵ/ k B , relaxation is drastically slowed down and that qualitatively low and high T data agree suggests the present process to be rather robust also experimentally. Motivated by that, we have shown recently that nanoporous monodisperse PS films can be generated and stabilized experimentally by an analogous procedure. , The single chain structures in expanded thin films and details of entanglement effects will be discussed in forthcoming work.…”

“…Our proposal is that this should lead to controlled nanoporous materials, which could be stabilized by quenching them well below T g . In refs and , we have demonstrated that a stable monodisperse nanoporous PS film can be easily created following a protocol analogous to molecular dynamics (MD) simulations to produce nanoporous films. Based on the concept of reptation tube diameters, we show a semiquantitative agreement of scattering function between simulation and experiment.…”

Smart Polymers for Soft Materials: From Solution Processing to Organic Solids

“…Recently, tuning the κ values of organic solids has attracted great attention. This has been achieved via macromolecular engineering, which has included the following: (1) tuning the microscopic (nonbonded) interactions in linear polymers and polymer blends [150][151][152][153][154]182] and (2) by using covalent bonds [163,[167][168][169]175,180,183,184].…”