Impact of key factors on the quality of birefringent microfigure printing using cellulose nanocrystals

Abstract

This study explores the optimization of printing conditions for birefringent microfigures (BMFs) using surface tension-directed assembly of cellulose nanocrystal (CNC)/polyvinyl alcohol (PVA) ink. Using CNCs derived from cotton (CCNC) and bacterial cellulose (BCNC), aqueous three-component PVA-based inks were developed to print high-precision BMFs on embossed copper molds. Key parameters—including CNC and PVA concentrations, CNC aspect ratio, solvent evaporation temperature, and mold surface topography—were thoroughly studied to determine the optimal printing conditions. Results demonstrated that increasing CNC content reduced ink viscosity, leading to significant improvements in print quality, which peaked at an optimal concentration. However, beyond these optimal values, excessive CNC content and higher temperatures adversely affected print clarity. The highest quality of BMFs was achieved when the solvent evaporation temperature was set at 80 °C, using a PVA concentration of 5 wt% and a CCNC-to-PVA ratio of 6 wt%. A quantitative framework was developed to assess print quality via polarized light microscopy, utilizing four control indicators. This study demonstrates the potential of surface tension-directed assembly of CNC/polymer ink for the high-fidelity production of BMFs, emphasizing potential applications in optical devices and advanced material design.