Solution Lithography for Colloidal Crystal Patterning: Revisiting Flory–Huggins Interaction Parameters and Co-Nonsolvent Systems

For fundamental studies and practical applications, colloidal crystal patterns on substrates are typically fabricated through etching and conventional lithography. However, a wet-chemical based method is necessary for simplifying the procedure, preserving the substrate structure, and reproducibly fabricating the colloidal crystal patterns. The present study demonstrates that colloidal crystal patterns can be conveniently generated using thermodynamic relationships between a polymer colloid and surrounding solvents. Close-packed colloidal monolayers in good solvents that cause colloidal swelling spontaneously transform into non–close-packed crystal patterns when non-solvents that cause their shrinkage replace the good solvents. The colloid diameter in the close-packed monolayer decreases significantly when the polymer in the colloid is passing thermodynamic theta conditions (when Flory–Huggins interaction parameters increase to higher than ≈0.5). The close-packed monolayers also transform into the patterns in co-nonsolvent conditions. The “solution lithography” might be particularly useful for patterning colloids on curved microstructures and plastic/flexible films. The colloidal shapes in the patterns vary with the solvent pairs and substrates. The method does not require special facilities to reproducibly fabricate the patterns. The study further suggests methods simultaneously fixing the patterns. The patterns exhibit anti-reflection properties. Therefore, the solution lithography is applicable to optics, electronics, analytical science, and energy systems.