Fabrication of large scale two-dimensional colloidal crystal of polystyrene particles by an interfacial self-ordering process.

Monolayer films of hexagonal close-packed polystyrene (PS) spheres were formed at the air-water interface through a self-ordering process without using Langmuir trough. The contact angle of PS particles on the surface of water was determined by an interfacial swelling method. It was found that the concentration and the nature of surfactant had an obvious influence on the arrangement of PS particles. PS suspension containing Triton X 100 (TX 100) of an appropriate concentration self-assembled into a closely packed monolayer on the surface of water. Sodium dodecyl sulfonate, an anionic surfactant, had a relative weak influence on the arrangement of pre-dried PS particles, in contrast, had an obvious effect on newly synthesized PS particles. Quantitative ultraviolet-visible (UV-vis) absorption spectrometry indicated that about 3% of the added TX 100 was adsorbed on the PS particle surface. Laser diffraction patterns on the monolayer film were used to investigate the lattice orientation. Ultraviolet-visible-near infrared (UV-vis-NIR) spectra of monolayer films of different sized PS particles displayed that the method presented here was universal for preparation of two-dimensional (2D) colloidal crystals.