Rapid Preparation of Liquid Photonic Crystals.

This study utilized a colloidal particle self-assembly method to rapidly prepare liquid photonic crystals (LPCs) stably dispersed in water. The submicrospheres with a diameter of 300-500 nm were synthesized by soap-free emulsion copolymerization of styrene (St) and 2-hydroxyethyl methacrylate (HEMA) and characterized by transmission electron microscopy and X-ray photoelectron microscopy. With the content of monomer HEMA increasing, the size and the hydration shell thickness of P-(St-HEMA) (PSH) submicrospheres also increased. The assembly mechanism of liquid crystals was explored by varying the volume fraction, ionic strength, solvent, and temperature. The results indicated that the ordered structure began to form at a low PSH volume fraction of 5% in water. As the ionic strength increased, the reflection wavelength was gradually redshifted, and the reflection intensity decreased. In addition, the addition of polar solvents and elevated temperature could reduce the strength of hydrogen bonding to destroy the ordered structure. It revealed that PSH particles could form long-range ordered structures in water through hydrogen bonding attraction and long-range electrostatic forces, which displayed bright colors. The LPC W/O emulsions and creams with high color saturation were prepared by simple emulsification, and the high-speed shear did not destroy the arrangement of liquid crystals, which laid the foundation for their further direct application in cosmetics.