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.
more »
« less
Toposelective vapor deposition of hybrid and inorganic materials inside nanocavities by polymeric templating and vapor phase infiltration
Selective deposition of hybrid and inorganic materials inside nanostructures could enable major nanotechnological advances. However, inserting ready-made composites inside nanocavities may be difficult, and therefore, stepwise approaches are needed. In this paper, a poly(ethyl acrylate) template is grown selectively inside cavities via condensation-controlled toposelective vapor deposition, and the polymer is then hybridized by alumina, titania, or zinc oxide. The hybridization is carried out by infiltrating the polymer with a vapor-phase metalorganic precursor and water vapor either via a short-pulse (atomic layer deposition, ALD) or a long-pulse (vapor phase infiltration, VPI) sequence. When the polymer-MO x hybrid material is calcined at 450 °C in air, an inorganic phase is left as the residue. Various suspected confinement effects are discussed. The infiltration of inorganic materials is reduced in deeper layers of the cavity-grown polymer and is dependent on the cavity geometry. The structure of the inorganic deposition after calcination varies from scattered particles and their aggregates to cavity-capping films or cavity-filling low-density porous deposition, and the inorganic deposition is often anisotropically cracked. A large part of the infiltration is achieved already during the short-pulse experiments with a commercial ALD reactor. Furthermore, the infiltrated polymer is more resistant to dissolution in acetone whereas the inorganic component can still be heavily affected by phosphoric acid.
more »
« less
- Award ID(s):
- 1921873
- NSF-PAR ID:
- 10353084
- Date Published:
- Journal Name:
- Nanoscale Advances
- ISSN:
- 2516-0230
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
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.more » « less
-
Elastomers are an important class of polymers for many applications. Often, additives are added to the polymer matrix of elastomers to promote vulcanization or enhance physical or chemical properties. In this study, vapor phase infiltration (VPI) is investigated for transforming unvulcanized cis -polyisoprene (from natural rubber) into an organic/inorganic hybrid material. Specifically, we examine single-cycle infiltration with diethylzinc (DEZ) and water to form infiltrated zinc oxide species. Interestingly, low-temperature pre-heating of the cis -polyisoprene acutely affects the processes of infiltration, including diffusivity, maximum solubility, and chemical reactivity. We attribute these effects to a combination of film relaxation and oxidation. Independent of thermal pre-treatments, all infiltration processes exhibited consistent zinc oxide loading irrespective of purge time between the DEZ and water doses, indicating the presence of a strongly bound intermediate state between the DEZ precursor and the cis -polyisoprene polymer. Increasing infiltration process temperature accelerates diffusion and lowers the maximum solubility, in accordance with Fick's law and gas phase sorption equilibrium. Resulting organic–inorganic hybrid films show enhanced resistance to dissolution in toluene, a good solvent for the pure polymer.more » « less
-
Polymer templates play an essential role in the robust infiltration-based synthesis of functional multicomponent heterostructures with controlled structure, porosity, and composition. Such heterostructures are be used as hybrid organic–inorganic composites or as all-inorganic systems once the polymer templates are removed. Using iron oxide/alumina heterostructures formed by two-step infiltration of polystyrene-block-polyvinyl pyridine block copolymer with iron and aluminum precursors from the solution and vapor-phases, respectively, we show that the phase and morphology of iron oxide nanoparticles dramatically depend on the approach used to remove the polymer. We demonstrate that thermal and plasma oxidative treatments result in iron oxide nanoparticles with either solid or hollow morphologies, respectively, that lead to different magnetic properties of the resulting materials. Our study extends the boundaries of structure manipulations in multicomponent heterostructures synthesized using polymer infiltration synthesis, and hence their properties.more » « less
-
more » « less
Abstract Versatile printing of polymers, metals, and composites always calls for simple, economic approaches. Here we present an approach to three-dimensional (3D) printing of polymeric, metallic, and composite materials at room conditions, based on the polymeric vapor-induced phase separation (VIPS) process. During VIPS 3D printing (VIPS-3DP), a dissolved polymer-based ink is deposited in an environment where nebulized non-solvent is present, inducing the low-volatility solvent to be extracted from the filament in a controllable manner due to its higher chemical affinity with the non-solvent used. The polymeric phase is hardened in situ as a result of the induced phase separation process. The low volatility of the solvent enables its reclamation after the printing process, significantly reducing its environmental footprint. We first demonstrate the use of VIPS-3DP for polymer printing, showcasing its potential in printing intricate structures. We further extend VIPS-3DP to the deposition of polymer-based metallic inks or composite powder-laden polymeric inks, which become metallic parts or composites after a thermal cycle is applied. Furthermore, spatially tunable porous structures and functionally graded parts are printed by using the printing path to set the inter-filament porosity as well as an inorganic space-holder as an intra-filament porogen.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2NA00291D
