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Vapor phase infiltration (VPI) is a vapor processing technique that converts polymers into organic–inorganic hybrid materials with modified properties. VPI of polymer membranes stabilizes against dissolution and swelling in organic liquids, opening up new opportunities for use in organic solvent reverse osmosis (OSRO) separations. However, the precise chemical structure of the infiltrated inorganic components remains poorly understood, limiting the potential to fully exploit process–structure–property relations for materials design and slowing the development of new hybrid membranes. This study explores the structural characteristics contributing to the chemical stability of PIM-1/ZnOxHy hybrid membranes through advanced spectroscopic techniques to clarify the chemistry and inorganic cluster formation in these materials that lead to enhanced stability in solvents that otherwise swell or dissolve the pure polymer. X-ray photoelectron spectroscopy (XPS) indicates a predominantly zinc hydroxide chemistry with higher proportions of oxide forming only at increasing cycle counts. Extended X-ray absorption fine structure (EXAFS) spectroscopy provides new understanding of the first and second coordination shells. These results indicate that the size of the clusters increases with prolonged VPI precursor exposure and additional VPI cycles, leading to improvements in membrane solvent stability. These findings offer a new understanding for how the physicochemical structure of these hybrid membranes can be characterized and then used to design for a desired performance. 

Vapor phase infiltration (VPI) is a post-polymerization modification technique that infuses inorganics into polymers to create organic–inorganic hybrid materials with new properties. Much is yet to be understood about the chemical kinetics underlying the VPI process. The aim of this study is to create a greater understanding of the process kinetics that govern the infiltration of trimethyl aluminum (TMA) and TiCl 4 into PMMA to form inorganic-PMMA hybrid materials. To gain insight, this paper initially examines the predicted results for the spatiotemporal concentrations of inorganics computed from a recently posited reaction–diffusion model for VPI. This model provides insight on how the Damköhler number (reaction versus diffusion rates) and non-Fickian diffusional processes (hindering) that result from the material transforming from a polymer to a hybrid can affect the evolution of inorganic concentration depth profiles with time. Subsequently, experimental XPS depth profiles are collected for TMA and TiCl 4 infiltrated PMMA films at 90 °C and 135 °C. The functional behavior of these depth profiles at varying infiltration times are qualitatively compared to various computed predictions and conclusions are drawn about the mechanisms of each of these processes. TMA infiltration into PMMA appears to transition from a diffusion-limited process at low temperatures (90 °C) to a reaction-limited process at high temperatures (135 °C) for the film thicknesses investigated here (200 nm). While TMA appears to fully infiltrate these 200 nm PMMA films within a few hours, TiCl 4 infiltration into PMMA is considerably slower, with full saturation not occurring even after 2 days of precursor exposure. Infiltration at 90 °C is so slow that no clear conclusions about mechanism can be drawn; however, at 135 °C, the TiCl 4 infiltration into PMMA is clearly a reaction-limited process, with TiCl 4 permeating the entire thickness (at low concentrations) within only a few minutes, but inorganic loading continuously increasing in a uniform manner over a course of 2 days. Near-surface deviations from the uniform-loading expected for a reaction-limited process also suggest that diffusional hindering is high for TiCl 4 infiltration into PMMA. These results demonstrate a new, ex situ analysis approach for investigating the rate-limiting process mechanisms for vapor phase infiltration. 

A solvent-free post-treatment process known as vapor phase infiltration (VPI) is used to engineer the organic solvent reverse osmosis (OSRO) performance of polymer of intrinsic microporosity 1 (PIM-1) membranes via infiltration of trimethylaluminum (TMA) metal-organic vapor. The infiltration of inorganic aluminum constituents hybridizes the pure polymer PIM-1 into an organic-inorganic material (AlOxHy/PIM-1) with enhanced chemical stability. A homogenous distribution of inorganic loading in PIM-1 is achieved due to the reaction-limited infiltration mechanism, and the OSRO performance is enhanced as a result. OSRO separations of ethanol/isooctane mixtures using these membranes are shown to be capable of breaking the azeotropic composition with a separation factor for ethanol over isooctane greater than 5 and an ethanol permeance of 0.1 Lm–2h–1bar–1. Thus, these organic-inorganic hybrid membranes created via VPI show promise as an alternative method for separating azeotropic liquid mixtures.