Periodic Stratified Porous Structures in Dynamic Polyelectrolyte Films Through Standing-Wave Optical Crosslinking for Structural Color

Periodic porous structures have been introduced into functional films to meet the requirements of various applications. Though many approaches have been developed to generate desired structures in polymeric films, few of them can effectively and dynamically achieve periodic porous structures. Here, a facile way is proposed to introduce periodic stratified porous structures into polyelectrolyte films. A photo-crosslinkable polyelectrolyte film of poly(ethylenimine) (PEI) and photoreactive poly(acrylic acid) derivative (PAA-N-3) is prepared by layer-by-layer (LbL) self-assembly. Stratified crosslinking of the PEI/PAA-N-3 film is generated basing on standing-wave optics. The periodic stratified porous structure is constructed by forming pores in noncrosslinked regions in the film. Thanks to the dynamic mobility of polyelectrolytes, this structural controlment can be repeated several times. The size of pores corresponding to the layer spacing of the film contributes to the structural colors. Furthermore, structural color patterns are fabricated in the film by selective photo-crosslinking using photomasks. Although the large-scale structural controlment in thick (micron-scale and above) films needs to be explored further, this work highlights the periodic structural controlment in polymeric films and thus presents an approach for application potentials in sensor, detection, and ink-free printing.

Automated summary

This paper presents a simple method to introduce periodic stratified porous structures into polyelectrolyte films. A photo-crosslinkable polyelectrolyte film was prepared by layer-by-layer self-assembly, and stratified crosslinking was generated based on standing-wave optics to form a periodic porous structure. Due to the dynamic mobility of the polyelectrolytes, structural control can be repeated, showing potential applications in sensors, detection, and ink-free printing.