Supporting Information
“Electrowetting based Infrared Lens using Ionic Liquids”
Xiaodong Hu,1 Shiguo Zhang,2 Yu Liu,1 Chao Qu,1 Liujin Lu,2 Xiangyuan Ma,2 Xiaoping Zhang*,1 and
Youquan Deng*,2
1
School of Information Science and Engineering, Lanzhou University, Lanzhou, China
Centre for Green Chemistry and Catalysis, Lanzhou Institute of Chemical Physics, CAS, Lanzhou, China
Email: ydeng@licp.cas.cn; zxp@lzu.edu.cn
2
1. Synthesis and Characterization of Ionic Liquids.
Five imidazolium ionic liquids with different cation and anion structures (Fig. S1), namely, 1-ethyl-3-methylimidazolium tetrafluoroborate
([EMIm][BF4]), 1-ethyl-3-methylimidazolium bisulfate ([EMIm][HSO4]), 1-butyl-3-methylimidazolium bisulfate ([BMIm] [HSO4]) and
1-hexyl-3-methylimidazolium bisulfate ([HMIm] [HSO4]), 1-ethyl-3-methylimidazolium perchlorate ([EMIm][ClO4]), were synthesized in
our laboratory according to the established procedures.
Figure S1. Formulas and structures of the ionic liquids studied.
Table SI shows the physical parameters of the compounds studied in this paper. All the data were got at 30 °C. Prior to measurements all
ILs were dried in vacuo at 80oC for 3 hours. The water content was ~650 ppm for [EMIm][BF4], ~660 ppm for [EMIm][HSO4], ~260 ppm
for [BMIm][HSO4], ~360 ppm for [HMIm][HSO4], ~620 ppm for [EMIm][ClO4].
Table SI. Surface tension and refractive index of compounds.
Compound
Surface tension (mN/m)
Refractive index
Dodecane
24.9
1.4201
H2O
71.2
1.3333
50.4
[EMIm][BF4]
1.4098
35.2
[EMIm][ClO4]
1.4762
63.1
[EMIm][HSO4]
1.5316
49.7
[BMIm][HSO4]
1.4968
33.2
[HMIm][HSO4]
1.4847
The refractive index was measured using DR-M2 abbe refractometer (ARTAGO (Japan)). The surface tension was measured on a
surface/interface analytical device (Solon Tech. (shanghai)) using the Du Noüy ring method. The water content was measured by
Karl-Fisher analysis (Metrohm KF coulometer).
2. Fabrication of ILs-based EVFLL
Details about the fabrication process are as follows. At first, an insulating layer of Parylene N was deposited on the steel cylinder (4 mm ×
Φ 4 mm) by chemical vapor deposition (10 μm, εr=2.65). Chemical Vapor Deposition: Equimolar of p-xylene and water vapor were mixed
at high temperature, the resulted p-xylene biradical was absorbed by an inert solvent at 90 ° C. The solvent was concentrated by evaporation.
The dimer of p-xylene was obtained by concentration, cooling, crystallization and filtration. At high temperature, the dimer was decomposed
into biradical. The resulted biradical was imported in the surface of lens, and compact parylene film was obtained after cooling and rapid
polymerization. Subsequently a thin hydrophobic layer top coating was deposited by dip-coating. The lens tube with insulating coating was
immersed in a 4% (w/v) of Teflon AF 1600 (DuPont) in FC 75, and then withdrawn from the solution at a constant speed of 750 μm/s. This
procedure was repeated twice. The Teflon-covered lens tube was heat-treated for 6 minutes at 112 °C, and 5 minutes at 165 °C, in order to
remove residual solvent and improve the adhesion of the Teflon layer to the substrate, which given a very thin Teflon coating (0.9 μm,
εr=1.93) as a top layer to obtain the desired hydrophobic and low hysteresis properties. As shown in Figure S2, utilizing ITO will discount
the transmittance of the lens, however this problem could be solved if we etch a hole on the ITO film as pattern in Figure S3 in the future. It
could guarantee the light path a good transmittance. It should be noted that the diameter of the hole has to be a little smaller than the inner
diameter of the lens tube, which keeps the contact between ITO film and ionic liquid in the lens tube and ensures them as an integral
electrode. The lens tube was glued onto the ITO glass with etching hole by ultraviolet plastic. Then ionic liquid (~20 μL) was injected into
the lens tube through a 10 μL syringe. Then dodecane was transferred into the cylinder with a pipette immediately in order to reduce
moisture. Finally, the top glass plate was glued onto the lens tube with ultraviolet plastic. All the fabrication processes were executed at room
temperature.
Figure S2. Transmittance of ITO for wavelength between 400 and 1100 nm.
Etching hole
ITO film
Figure S3. The pattern of etching hole on the ITO film
3. Surface roughness of Parylene and Teflon films
The surface roughness parameters of Parylene and Teflon films have been tested by AFM. The results are shown in Table SII, and the
AFM morphologies are shown in Figure SII.
Table SII. Surface roughness parameters of Parylene and Teflon films.
Parameter
Description
Parylene film (nm) Teflon film (nm)
Rp
maximum peak height
470.096
258.599
Rv
maximum valley depth
-224.185
-193.378
Rt
maximum height of the profile
694.281
451.977
Ra
arithmetic average of absolute values
55.237
50.309
Rq
root mean squared
69.135
63.298
Figure S4. The AFM morphologies of Parylene and Teflon films.
4. Schematic of meniscus curvature variation
Figure S5.
The curvature of the meniscus of ILs-based EVFLL under different voltages.
5. Other experimental results
Figure S6. Change of focal length of [EMIm][ClO4]-based EVFLL with different volume of the ILs.
Figure S7. Change of focal length of [EMIm][ClO4]-based EVFLL with different diameter of the lens.
Figure S8. Change of focal length of [EMIm][ClO4]-based EVFLL with different thickness of the insulting layer.