Supporting Information
Preparation of free-standing two-dimensional colloidal crystal arrays
Fei Xue, Zihui Meng*, Fenglian Qi, Min Xue*,Lili, Qiu
School of Chemical Engineering and Environment, Beijing Institute of Technology,
Beijing, China, 100081
Experimental
Materials
Methyl methacrylate (MMA) was purchased from Sigma and used as received.
Potassium persulfatewere obtained from Aladdin Co. Ltd. Toluene, DMSO, acetone,
chloroform, ethyl acetate and acetonitrile were purchased from Sinopharm Chemical
Reagent Co., Ltd. Deionized water (Aquapro) was used for the experiment. Common
glass slides (22×22×0.15 mm) and metal meshes (Weiss Experiment Products Co.
Ltd.) were used in this research. Before use, the glass slides were immersed in a
H2SO4-H2O2 mixture (7:3) for 12 h, and then rinsed with deionized water in an
ultrasonic bath for three times and then dried for use. The metal meshes were used as
received.
1 Preparation of monodisperse PMMA particles with different diameters
Monodisperse PMMA particles of 262 nm diameter were polymerized by a previously
reported emulsifier-free emulsion polymerization method1. These seed PMMA
particles were washed thoroughly with deionized water and diluted with water to give
a final concentration of 0.03 g/mL.
PMMA particles with larger sizes of 530, 620 and 740 nm were prepared by a seeded
emulsifier-free emulsion polymerization method. Briefly, 25 mL of the seed PMMA
suspension solutions were added to 90 mL deionised water in a four-neck
round-bottom flask with a condenser. The solution was deoxygenated by bubbling
with nitrogen for half an hour. The solution was then heated to 80 ºC followed by
injections of a 5 mL potassium peroxydisulfate solution (0.2 g) and a certain amount
of MMA (5, 10, and 20 mL) was added through a side neck of the flask. A
temperature sensor monitored the reaction temperature. The mixture was then
refluxed for 45 min while being stirred at 300 rpm. After polymerization, the
monodisperse PMMA particles of 530, 620, and 748 nm in diameter were washed
with deionized water. The pure PMMA suspension was dried in drier under 60 ℃.
2 Preparation of free-standing 2D PMMA colloidal crystal arrays
20 mg dried PMMA particles of 530, 620 and 740 nm was added into 0.5 mL toluene
and mixed for 30 s. During this time, PMMA particles partially dissolved in the
toluene phase. Directly drop one droplet of the toluene suspension of PMMA particles
on water surface where the particles spread to assemble into a close-packed 2D
colloidal crystal array at the air/water interface in a 7.5 cm diameter glass dish.
Free-standing 2D colloidal crystal array films formed upon toluene evaporation in air.
Transfer these films by picking up them by glass slide and metal mesh.
3 Characterization of free-standing 2D PMMA colloidal crystal arrays
Gold layers were sputtered onto the resultant 2D colloidal crystal arrays. The particles,
their orderings and morphologies were examined with an SEM (Quanta FEG 250,
FEI). Debye diffraction rings were measured to characterize the forward light
diffraction of the 2D colloidal crystal arrays2. A 405 nm violet-blue laser pointer
illuminated the surface of the 2D colloidal crystal arrays at normal incidence. The
photographs of the CCHs were taken using a digital camera at an angle of ~30°
between the light source/camera and the colloidal crystal array normal. The 2D
colloidal crystal arrays were placed on an aluminum mirror.
Fig. S1 Free-standing 2D PMMA colloidal crystal arrays prepare with 2 (a) and 4 (b)
min operation time using toluene as solvent
Fig. S2 Free-standing PMMA films prepared with different operation time (1、2、4、
6、9、12 min) using toluene/ethyl ether as solvent
Fig. S3 SEM images of monodisperse PMMA particles with diameters of 530 (a), 620
(b), and 740 nm (c). The scale bars are 1μm in length.
References
1.
F. Xue, Z. Meng, Y. Wang, S. Huang, Q. Wang, W. Lu and M. Xue, Analytical Methods, 2014,
6, 831-837.
2.
J.-T. Zhang, X. Chao, X. Liu and S. A. Asher, Chemical Communications, 2013, 49,
6337-6339.