Controlling wettability, wet strength, and fluid transport selectivity of nanopaper with atomic layer deposited (ALD) sub-nanometer metal oxide coatings

Abstract

Nanocellulosic films (nanopapers) are of interest for packaging, printing, chemical diagnostics, flexible electronics and separation membranes. These nanopaper products often require chemical modification to enhance functionality. Most chemical modification is achieved via wet chemistry methods that can be tedious and energy intensive due to post-processing drying. Here, we discuss the use of atomic layer deposition (ALD), a vapor phase modification technique, to quickly and simply make nanopaper hydrophobic and enhance its wet strength and durability. Specifically, we find that just "a few" ALD cycles (#10) of either aluminum oxide or titanium oxide is sufficient to significantly increase the durability of cellulose nanofibril (CNF) paper in aqueous media, even under aggressive sonication conditions. Keeping the number of ALD cycles low makes the process more scalable for commodity manufacturing. We investigate whether this increase in wet strength is due to enhanced hydrophobic attractions or stronger hydrogen bonding between CNF fibers. The current evidence suggests that the latter mechanism is likely dominant, with ab initio calculations suggesting that newly created M-OH terminations on the cellulose nanofibrils increase hydrogen bond strength between fibers and impede CNF hydration and dispersion. ALD treated nanopapers are also found to preferentially transport hexane over water, suggesting their potential use in oil/water demulsification devices.

Reaction–Diffusion Transport Model to Predict Precursor Uptake and Spatial Distribution in Vapor-Phase Infiltration Processes

“…In this way, the model presented here captures the transition from VPI behavior to a self-limiting surface coating behavior similar to atomic layer deposition (ALD). This type of surface coating behavior has been seen experimentally in vapor-phase treatments of polymers such as cellulose, poly­(vinyl alcohol), and poly­(acrylic acid), which possess high concentrations of reactive functional groups. ,− …”

Layer-by-Layer Spray-Coating of Cellulose Nanofibrils and Silver Nanoparticles for Hydrophilic Interfaces

“…49 Furthermore, the water contact angles of AC and AM samples measured after three months of storing in ambient conditions are almost the same with that measured immediately after synthesis, suggesting an excellent stability of the AgNP/CNF films. Tailorable wettability 26,50 is crucial for the functionalization of thin films with antifouling, 51 detergent-free cleaning, 52 or antifogging 53 properties in biomedical and industrial applications.…”

Single-Cycle Atomic Layer Deposition on Bulk Wood Lumber for Managing Moisture Content, Mold Growth, and Thermal Conductivity

“…Reacting hydrophilic cellulosic materials with a single ALD cycle of metalorganic or metal halide precursors and water oftentimes leads to a metal oxide surface chemistry that attracts adventitious carbon and increases surface hydrophobicity. This phenomenon is well-documented in the literature. − However, to our knowledge, this treatment has never been reported for wood lumber. While this hydrophobicity is often retained up to several (3 to 10) ALD cycles, at high cycle numbers (>10 cycles), the material often returns to being hydrophilic.…”