Mechanical and chemical robustness of the aluminum oxide-infiltrated block copolymer films and the resulting aluminum oxide coatings

Abstract

Block copolymer (BCP) templates have been widely used for the design of functional organic-ceramic composites and ceramic structures. In this study, we explore the mechanical characteristics of such structures designed using sequential infiltration synthesis (SIS). We demonstrate that SIS significantly reinforces the BCP template and decreases their sensitivity to temperature and chemical environment. We also probe tribological characteristics of nanoporous alumina films obtained from the organic-ceramic composites after the BCP template removal. We determined with atomic force microscopy (AFM) that the lateral forces between the tip and the substrate are highly affected by the surface reactivity, surface structure, area of contact, environment, and porosity accessibility and interconnectivity. As confirmed by the quartz crystal microbalance (QCM) analysis, the high accessibility of the pores in the alumina film to the water penetration leads to a decrease in the friction for the ~4 μm in size colloidal tip sliding against the nanoporous alumina in contrast to the bulk alumina. The effect diminishes once the size of the AFM probe becomes comparable to the size of the pores, which is attributed to the limited water flow under the tip to support the applied during sliding stresses. Understanding the surface structure and its effect on the mechanical and frictional characteristics of materials is important for the predictive design of coatings that can sustain thermomechanical stresses and can be used to enhance the lubrication of fluids in various mechanical systems.