Search for: All records

In situ optical measurements during chemical vapor deposition processes can offer insight into the chemical reactions and electronic phenomena that are occurring during a process. However, the tooling to make these measurements can be complex, difficult to align, and may even require a redesign of the entire vacuum deposition chamber. Herein, we present a setup that allows for in situ optical measurements using vacuum-compatible fiber optics that only requires a singular conflat feedthrough, eliminating the need for optical viewports and alignment of external light sources/detectors. Proof of performance is shown with a neutral density filter and an exemplary application of vapor doping a conjugated polymer (poly-3-hexylthiophene) using vapor-phase TiCl4. 

Vapor-phase infiltration (VPI) presents a promising approach to enhancing the stability of organic membranes in organic solvents while maintaining critical properties, such as membrane permeance and selectivity. However, the precise chemical structure of the infiltrated inorganics and their impact on solvent stability remain poorly understood, limiting efforts to improve VPI treated hybrid membrane technology for organic solvent reverse osmosis (OSRO). This study uses X-ray absorption spectroscopy alongside X-ray photoelectron spectroscopy (XPS) to elucidate the inorganic cluster structure within PIM-1/AlOxHy. By analyzing the H2O ratio via XPS and assessing the first and second shell Al coordination numbers from Al K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, we propose that aluminum oxyhydroxide tends to form nonlinear networked structures. X-ray absorption near-edge spectroscopy (XANES) analysis confirms a predominantly six-coordinate structure in the first shell, while EXAFS analysis of the second shell reveals the presence of three aluminum atoms, suggesting clusters significantly larger than simple dimers or trimers, similar to larger aluminum hydroxide and oxyhydroxide crystal structures. Furthermore, we demonstrate that postprocessing techniques, such as dehydration and rehydration, can be utilized to control this network structure and membrane permeance and selectivity without compromising solvent stability. 

Herein, we report for the first time the use of vapor phase infiltration (VPI) to infuse conducting polymers with inorganic metal oxide clusters that together form a photocatalytic material. While vapor infiltration has previously been used to electrically dope conjugated polymers, this is the first time, to our knowledge, that the resultant hybrid material has been demonstrated to have photocatalytic properties. The system studied is poly(3-hexylthiophene-2,5-diyl) (P3HT) vapor infiltrated with TiCl4 and H2O to create P3HT-TiOx organic–inorganic hybrid photocatalytic materials. X-ray photoelectron spectroscopy analysis shows that P3HT-TiOx VPI films consist of a partially oxidized P3HT matrix, and the infiltrated titanium inorganic is in a 4+ oxidation state with mostly oxide coordination. Upon visible light illumination, these P3HT-TiOx hybrids degrade methylene blue dye molecules. The P3HT-TiOx hybrids are 4.6× more photocatalytically active than either the P3HT or TiO2 individually or when sequentially deposited (e.g., P3HT on TiO2). On a per surface area basis, these hybrid photocatalysts are comparable or better than other best in class polymer semiconductor photocatalysts. VPI of TiCl4 + H2O into P3HT makes a unique hybrid structure and idealized photocatalyst architecture by creating nanoscale TiOx clusters concentrated toward the surface achieving extremely high catalytic rates. The mechanism for this enhanced photocatalytic rate is understood using photoluminescence spectroscopy, which shows significant quenching of excitons in P3HT-TiOx as compared to neat P3HT, indicating that P3HT acts as a photosensitizer for the TiOx catalyst sites in the hybrid material. This work introduces a new approach to designing and synthesizing organic–inorganic hybrid photocatalytic materials, with expansive opportunities for further exploration and optimization. 

This study examines the chemical reaction pathways for vapor phase infiltration (VPI) of TiCl4 into poly(methyl methacrylate) (PMMA). VPI is a processing method that transforms organic polymers into organic−inorganic hybrid materials with new properties of interest for microelectronic patterning, technical textiles, and chemical separations. Understanding the fundamental chemical mechanisms of the VPI process is essential for establishing approaches to design the chemical structure and properties of these hybrid materials. While prior work has suggested that TiCl4 infiltration into PMMA does not disrupt the polymer’s carbonyl bond, a clear reaction mechanism has yet to be proposed. Here, we present a detailed X-ray photoelectron spectroscopy study that presents evidence for a concerted reaction mechanism that involves TiCl4 coordinating with the PMMA’s ester group to dealkylate the methyl side group, creating a chloromethane byproduct and primary chemical bonds between the organic and inorganic components of the hybrid material. Additional spectroscopy, quartz crystal microbalance gravimetry, and thermophysical and chemical property measurements of this material, including solubility studies and thermal expansion measurements, provide further evidence for this chemical reaction pathway and the subsequent creation of inorganic cross-links that network these TiOx−PMMA hybrid materials. 

This study investigates the use of TiCl4 vapor phase infiltration (VPI) to cleave ester groups in the main chain of a polymer and drive depolymerization and film etching. Prior investigations have demonstrated that the infiltration of TiCl4 into PMMA results in dealkylation of its ester bond, cleaving its side groups. This study investigates the VPI of TiCl4 into poly(lactic acid), which is a prototypical polymer with an ester group in its main chain. Utilizing in situ quartz crystal microbalance (QCM) measurements and spectroscopic ellipsometry, PLA is observed to depolymerize readily at 135 °C with extended TiCl4 precursor exposure, resulting in significant thickness and mass reduction, whereas at 90 °C, depolymerization is significantly slower and etching is negligible. Utilizing Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and a residual gas analyzer (RGA), dealkylation is shown to be the primary depolymerization mechanism. FTIR and XPS analyses reveal the consumption of carbonyl and methoxy groups and the emergence of hydroxyl, chlorine, and titanium moieties. In situ RGA measurements provide further insights into the byproducts formed during the TiCl4 and water exposure steps, indicating that the depolymerized components undergo further breakdown into other substances. Residuals left after 135 °C TiCl4 VPI are easily removed with a 0.1 M HCl aqueous solution. These findings highlight the expanding functionality of VPI, revealing its capability as both an additive and subtractive process and suggesting its broader applications. 

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. 

Vapor phase infiltration (VPI) enables the fabrication of novel organic–inorganic hybrid materials with distinctive properties by infiltrating polymers with inorganic species through a top-down approach. However, understanding the process kinetics is challenging due to the complex interplay of sorption, diffusion and reaction processes. This study examines how polymer network flexibility affects the kinetics of diethylzinc (DEZ) infiltration into a highly crosslinked polyacrylate copolymer system composed of two monomers: trimethylolpropane triacrylate (TMPTA) and ethoxylated trimethylolpropane triacrylate (ETPTA). The findings show that increasing the ratio of ETPTA, which enhances network flexibility, facilitates precursor diffusion, resulting in deeper infiltration and faster saturation. A reaction–diffusion transport model is employed to qualitatively interpret the experimental results and gain insights into the underlying process mechanisms, thus contributing to a better understanding of VPI kinetics. 

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. 

In this work, the vapor-phase infiltration (VPI) of polyethylene terephthalate (PET) fabrics with trimethylaluminum (TMA) and coreaction with water vapor is explored as a function of limiting TMA reagent conditions versus excess TMA reagent conditions at two infiltration temperatures. TMA is found to sorb rapidly into PET fibers, with a significant pressure drop occurring within seconds of TMA exposure. When large quantities of polymer are placed within the chamber, minimal residual precursor remains at the end of the pressure drop. This rapid and complete sorption facilitates the control of inorganic loading by purposely delivering a limited quantity of the TMA reagent. The inorganic loading for this system scales linearly with a Precursor:C=O molar ratio of up to 0.35 at 140 °C and 0.5 at 80 °C. After this point, inorganic loading is constant irrespective of the amount of additional TMA reagent supplied. The SEM analysis of pyrolyzed hybrids indicates that this is likely due to the formation of an impermeable layer to subsequent infiltration as the core of the fibers remains uninfiltrated. The Precursor:C=O molar ratio in the subsaturation regime is found to tune the hybrid fabric morphology and material properties such as the optical properties of the fabric. Overall, this work demonstrates how a reagent-limited processing route can control the inorganic loading in VPI synthesized hybrid materials in a simpler manner than trying to control kinetics-driven methods.