Selective Light-Induced Nanowetting: Hierarchical Polymer Nanoarrays With Erasability And Rewritability Via Photofluidization

Although various polymer nanostructures can be fabricated by template-based wetting methods, it is still a great challenge to achieve effective pattern control, primarily due to the nonselectivity of polymers responding to external stimuli. In this work, we present a versatile selective light-induced nanowetting method to fabricate hierarchical polymer nanoarrays. This strategy is based on the selective wetting abilities of polymer chains via photoliquefaction of azobenzene-containing polymers (PAzo) into the nanopores of anodic aluminum oxide (AAO) templates. Phase-separated films of polystyrene (PS) and PAzo with different ratios are used as a model system to demonstrate the feasibility and versatility of this light-induced nanowetting method. Upon exposure to UV light, the azobenzene groups in the PAzo exhibit the trans-cis photoisomerization, causing the glass transition temperatures (T-g) of the PAzo to be lower than the room temperature. As a result, the PAzo domains in the microphase-separated polymer blend films are selectively fluidized and wet the nanopores of the AAO templates while the PS domains remain in the glassy state. The PAzo chains are then solidified by illuminating with visible light, resulting in the formation of PAzo nanoarrays on selective regions. The sizes of the hierarchical nanostructures can be controlled by both the domain sizes of the PS/PAzo blends and the pore sizes of the AAO templates. Furthermore, erasability and rewritability of this strategy are demonstrated by repeatedly shining the polymer blend samples with UV and visible light. Compared with the traditional template wetting methods, this versatile method endows the selective wetting ability of polymers without heating and exposure to volatile organic solvents.