Effect of Al2O3 ALD coating and vapor infusion on the bulk mechanical response of elastic and viscoelastic polymers

• ALD was used to modify the bulk mechanical properties of industrial polymers.
• It was found dose times of precursors led to subsurface and surface modification of the polymers.
• The subsurface modification was found to affect the mechanical response of the polymer materials.
• The change in mechanical response was ascribed to diffusion of precursors into the polymer.
• The results demonstrate ALD can modify the bulk mechanical properties of polymers.

Polymer films and fibers are often coated with thin films by techniques including sputtering, chemical vapor deposition (CVD) and atomic layer deposition (ALD), to add resilience, impede water transport and provide chemical functionalization. Vapor processing also allows chemical precursors to diffuse and react in the near surface and bulk regions of the polymer. In this work we investigate how low temperature ALD Al2O3 coatings formed at < 100 °C modify bulk mechanical properties of nylon 6, polypropylene, and Pellethane, a commercial polymer elastomer. Transmission electron microscopy shows evidence for subsurface reactant penetration for all these polymers. The ALD treatment tends to increase the Young's modulus during the first ~ 200 ALD cycles, especially for the nylon 6 and elastomer, consistent with the expected polymer/precursor reactivity. However, the ALD coating generally embrittles the polymers, causing them to rupture under smaller applied strain. The embrittlement, however, is minimal for the viscoelastic polymer, so that the improved modulus during ALD treatment could improve its overall mechanical strength and performance. Chemical mechanisms for the mechanical changes are discussed. Overall, the results suggest that further analysis of ALD processes could lead to new means to improve mechanical function of synthetic polymers.