Gas Permeation of Sulfur Thin-Films and Potential as a Barrier Material

Elemental sulfur was formed into poly(ether sulfone)-supported thin-films (ca. 10 µm) via a melt-casting process. Observed permeabilities of C2H4, CO2, H2, He, and N2 through the sulphur thin-films were <1 barrer. The sulfur thin-films were observed to age over a period of ca. 15 days, related to the reversion of polymerized sulfur to the S8 allotrope. This structural conversion was observed to correlate with an increase in the permeability of all gases.


S1. Contextualization of novelty statements for the major areas of novelty identified in this work
The following sections describe the search methodology used to contextualize the novelty of our proposed research and understand the surrounding science in the areas of sulfur-derived polymers (ESI Section S2.1) and sulfur-based barrier materials (ESI Section S2.2). In all cases, a selection of relevant references have been included in the main manuscript and full research notes can be obtained from the authors upon request.

S1.1 Contextualization of novelty statement for sulfur-derived polymers
Key idea for contextualization: Scope of academic research on sulfur-derived polymeric materials. The titles and first three lines of the abstracts as provided by google scholar were read. Papers of particular interest, especially review papers were selected and read in depth.

Summary of results (if not included in the publication):
A range of applications and review articles were identified, providing background reading for the project. No evidence of references associated with the study of gas permeation through these materials was identified. Several key reviews were selected for further study including: "Recent Approaches for the Direct Use of Elemental Sulfur in the Synthesis and Processing of Advanced Materials" 2 "Sulfur and Its Role In Modern Materials Science" 3 "Green chemistry and polymers made from sulfur" 4 Citations of these papers were selected for examination.
Were additional keywords / search methods identified: Yessee additional CON statement(s) The titles and first three lines of the abstracts as provided by google scholar were read. Papers of particular interest, especially review papers were selected and read in depth.

Summary of results (if not included in the publication):
A range of applications and review articles were identified, providing background reading for the project. No evidence of references associated with the study of gas permeation through these materials was identified. Judged at this point a sufficient overview of the field had been obtained.
Were additional keywords / search methods identified: Yessee additional CON statement(s)

S2.1 Thermogravimetric analysis (TGA)
One TGA study was undertaken on sulfur powder (S8) to check the phase transition under N2 atmosphere over a period time of 5 h. To summarize, the TGA results show that S8 didn't show obvious mass loss until 200 °C, and the mass loss after 200 o C is due to sublimation. The temperature profile used was equilibrate to 50 °C, then ramped to 300 °C at 10 °C/min under N2 environment. Fig S1. TGA data for sulfur powder (S8) using the mass at 50 °C as the reference for the relative mass calculation.

S2.2 Differential Thermal Analysis (DTA)
One DTA study was undertaken on sulfur powder (S8) to check the phase transition under N2 atmosphere over a period time of 5 h. To summarize, the DTA results shown that S8 experienced 3 phase transitions during the testing time. The phase transition was happened at 103.8 °C, 109.6 °C and 172.4 °C. The membrane was hence processed at temperatures above the third phase transition point, i.e., 175 °C, due to the fast mobility and lower viscosity of the melt observed at this temperature.