Pore Network Percolation in Polymers of Intrinsic Microporosity Examined by Gaseous and Antimatter Probes

TL;DR

This paper explores how pore accessibility in a type of polymer called PIMs is influenced by network percolation using both gaseous and antimatter probes.

Contribution

The study introduces a percolation model to explain pore accessibility in PIMs and uses antimatter probes to detect buried pores.

Findings

Buried pores in PIMs are detected using positron-based Doppler broadening spectroscopy.

Pore accessibility in PIMs is linked to network percolation behavior.

Nonpercolated networks in PIMs contain inaccessible pores.

Abstract

Synthesis of polymers
with tailored properties requires an understanding
of the underlying phenomena leading to these properties. Polymers
of intrinsic microporosity (PIMs) are non-network polymers with a
substantial guest-accessible free volume. Their BET surface areas
have been reported to be as high as 1000 m2/g, and their
porosity has led to the demonstration of some of the best membrane-based
gas separations to date. However, it has been challenging to predict
porosity in PIMs a priori, in part due to an incomplete framework
for understanding the origins of porosity in these materials. Here,
porosity in several archetypal PIMs is examined through the lens of
a percolation model, whereby porosity in oligomers follows behavior
expected for nonpercolated and percolated networks. Positron-based
Doppler broadening spectroscopy is used to examine buried pores in
samples whose pores are inaccessible to typical (nonantimatter) guests
and demonstrate that buried pores are present in PIMs with nonpercolated
pore networks. Taken together, the findings are in agreement with
the contention that network percolation plays a critical role in pore
accessibility in PIMs.

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