Temperature-Dependent Subsurface Growth during Atomic Layer Deposition on Polypropylene and Cellulose Fibers

Abstract

Nucleation and subsequent growth of aluminum oxide by atomic layer deposition (ALD) on polypropylene fiber substrates is strongly dependent on processing temperature and polymer backbone structure. Deposition on cellulose cotton, which contains ample hydroxyl sites for ALD nucleation and growth on the polymer backbone, readily produces a uniform and conformal coating. However, similar ALD processing on polypropylene, which contains no readily available active sites for growth initiation, results in a graded and intermixed polymer/inorganic interface layer. The structure of the polymer/inorganic layer depends strongly on the process temperature, where lower temperature (60 degrees C) produced a more abrupt transition. Cross-sectional transmission electron microscopy images of polypropylene fibers coated at higher temperature (90 degrees C) show that non-coalesced particles form in the near-surface region of the polymer, and the particles grow in size and coalesce into a film as the number of ALD cycles increases. Quartz crystal microbalance analysis on polypropylene films confirms enhanced mass uptake at higher processing temperatures, and X-ray photoelectron spectroscopy data also confirm heterogeneous mixing between the aluminum oxide and the polypropylene during deposition at higher temperatures. The strong temperature dependence of film nucleation and subsurface growth is ascribed to a relatively large increase in bulk species diffusivity that occurs upon the temperature-driven free volume expansion of the polypropylene. These results provide helpful insight into mechanisms for controlled organic/inorganic thin film and fiber materials integration.

Progress and future directions for atomic layer deposition and ALD-based chemistry

“…36 At higher temperatures, enhanced diffusion leads to surface roughening that is not observed for coatings formed at lower temperatures ( Figure 5 ). 35 Pulsed or sequential vapor infi ltration can also completely saturate the bulk/precursor reaction, yielding full chemical modifi cation of the starting polymer. After exposing polybutylene terephthalate microfi bers to TMA and H 2 O for 18 hours and 1 hour, respectively, at 80°C, mass uptake and infrared transmission data indicated that the starting polymer was completely converted to a hybrid organic-inorganic solid, as shown in Figure 6 .…”

Highly conductive and flexible fiber for textile electronics obtained by extremely low-temperature atomic layer deposition of Pt

“…In particular, textile electronics using the ALD is one of the promising fields since several materials can be readily deposited at temperatures lower than 150°C by ALD, leading to the effective functionalization of thermally fragile substrates such as plastics, cellulose papers and polymeric textiles. [9][10][11][12] Chen et al 13 demonstrated hydrophobic silk fabrics with a high laundering durability and robustness due to a TiO 2 coating deposited by ALD. However, in the case of metal ALD, since temperatures as high as 300°C are generally required to achieve successful deposition with the thermal energy of the precursor reactions, it is difficult to deposit conformal metal films onto thermally weak substrates using ALD, causing difficulties in a wide range of applications, including textile electronics.…”

Hydrophilization of porous polypropylene membranes by atomic layer deposition of TiO2 for simultaneously improved permeability and selectivity

“…Al 2 O 3 , ZrO 2 , TiO 2 and so on) have been investigated on various types of polymer substrates during the ALD process [18][19][20][21][22][23][24][25]. A model was proposed for the ALD precursors' adsorption on surface and diffusion into the subsurface of polymers without active groups [19], and it was found that the process temperature significantly affected the interface between the deposition layer and the substrate [26,27]. There are some reports on the deposition of metal oxides by ALD on PP substrates but most studies are focused on the deposition of metal oxides, mainly Al 2 O 3 , on nonporous PP films [19,[27][28][29][30].…”