Tunable Surface Nanotopography with Disordered Hyperuniformity in Poly(ethylenimine)/Alginate-Based Multilayered Films

Polyelectrolyte multilayer (PEM) films with controllable surface morphology, formed by layer-by-layer (LbL) assembly, are widely used in energy, water, sensors, electronics, and biomedical applications. Self-wrinkling behavior could give rise to diverse micro- or nanoscale patterns in these PEM films in response to various stimuli, thereby enabling the desired functionalities. Disordered hyperuniformity (DHU) is a recently discovered exotic state of matter that demonstrates disorder on a local scale but uniformity in long-range order. It has been found that the DHU states of solid 2D materials and high-entropy alloys often possess significantly lower energy than other disorder models and can lead to unique electronic and thermal transport properties. Nevertheless, a surface with DHU-like nanostructures in PEM films has never been reported before. Herein, we present a straightforward method for generating DHU-like nanotopographic patterns in PEM films. Using polyelectrolyte solutions of branched poly(ethylenimine) (BPEI) and alginate (ALG), the resultant LbL films showed tunable nanodot and nanopore-like topographies on the surface, depending on the pH of the solutions and the number of layers. The experimental results demonstrated that the pH of the terminal solution during the LbL process played a dominant role in determining the nanostructures of the final film, which is due to the different degrees of ionization of polyelectrolyte chains under different pH environments. Notably, the nanostructures with DHU-like characteristics were observed on the film surface within a narrow pH range for BPEI and ALG. Benefiting from the DHU “phase diagram” based on the autocovariance function analysis, the nanofilms with specific surface characteristics and desired functionalities can be created. Moreover, the nano- or microfeatures on the surface could be retained by introducing SiO₂ nanoparticles into the PEM matrix, indicating the possibility of manufacturing functional nanocomposite-incorporated films.