Interpreting inorganic compositional depth profiles to understand the rate-limiting step in vapor phase infiltration processes

Abstract

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...

Dealkylation of Poly(methyl methacrylate) by TiCl4 Vapor Phase Infiltration (VPI) and the Resulting Chemical and Thermophysical Properties of the Hybrid Material

“…At 120 °C (Figure a) Ti is uniformly present throughout the entire depth, and the concentration increases from ∼1.5 to ∼3 at. % as the TiCl 4 exposure time is increased from 1 to 12 h. Above 12 h of exposure time, the inorganic loading approximately saturates Figure a corroborates the reaction-limited profile observed in our previous paper at 135 °C; however, we observe a lower overall titanium concentration due to the lower processing temperature .…”

“…% as the TiCl 4 exposure time is increased from 1 to 12 h. Above 12 h of exposure time, the inorganic loading approximately saturates. 23 Figure 5a corroborates the reactionlimited profile observed in our previous paper at 135 °C; however, we observe a lower overall titanium concentration due to the lower processing temperature. 23 A similar trend is observed at a VPI process temperature of 150 °C (Figure 5b).…”

“…These properties often provide evidence of whether chemical cross-links, via primary chemical bonds, are formed between the organic and inorganic constituents. Specifically, we have investigated the TiO x –PMMA hybrids prepared at infiltration temperatures of 120 and 150 °C at varying hold times because these films are expected to be fully infiltrated throughout the entire film depth Figure presents XPS depth profiling data for 120 °C (Figure a) and 150 °C (Figure b) infiltration into 200 nm PMMA films at varying exposure times.…”

“…The general process sequence was (1) ultrahigh purity N 2 gas was flowed into the reactor to purge the system for 5 min, (2) the system was pumped down to base vacuum (30 mTorr) for an hour for full removal of water, (3) the chamber was isolated, (4) the TiCl 4 precursor valve, which is connected directly to the chamber, was opened for 5 s to reach a vapor pressure of about 1 Torr of TiCl 4 , (5) the TiCl 4 was then held in the chamber for between 1 and 48 h, (6) the system was then pumped to base vacuum for 5 min, (7) the water co-reactant valve, which is also connected directly to the chamber, was opened for 1 s to give a vapor pressure of 1.8 Torr in the chamber, and (8) the water was held in the chamber for 1 h before purging the system for 60 s and venting to the atmosphere. 23 In Situ Quartz Crystal Microbalance (QCM) Gravimetry Measurements. QCM experiments were performed in a hot-walled custom-built VPI reactor described elsewhere.…”

“…2 In prior work, we have demonstrated that TiCl 4 infiltration into PMMA occurs via a reaction-limited mechanism. 23 Unlike TMA infiltration, TiCl 4 infiltrates uniformly, albeit more slowly, within the entire depth of a PMMA thin film�that is to say, the TiCl 4 rapidly diffuses into the PMMA, but entrapment is limited by the reaction rate. While this prior study clarified the rate-limiting step for the VPI process kinetics�the chemical reaction�the exact chemical mechanisms for this reaction process were not clarified.…”