Highly Clear and Transparent Nanoemulsion Preparation under Surfactant-Free Conditions Using Tandem Acoustic Emulsification

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1 Supplementary Information Highly Clear and Transparent Nanoemulsion Preparation under Surfactant-Free Conditions Using Tandem Acoustic Emulsification Koji Nakabayashi, a Fumihiro Amemiya, a Toshio Fuchigami, a Kenji Machida, c Sekihiro Takeda, c Kenji Tamamitsu, c and Mahito Atobe*, a,b a Department of Electronic Chemistry, Tokyo Institute of Technology, Yokohama , Japan. b Department of Environment and System Sciences, Yokohama National University, Yokohama , Japan. c Research Center, Nippon Chem-Con Co., Takahagi , Japan. 1. Materials All chemicals were used without further purification. 3,4-Ethylenedioxythiophene (EDOT) was purchased from Sigma-Aldrich Co.. Lithium perchlorate (LiClO 4 ) was purchased from Kanto Chem. Co.. Distilled and deionized water was used as a solvent for electropolymerization. 2. Tandem acoustic emulsification 0.5 mmol of EDOT was added to 25 ml of aqueous solution containing 1.0 M LiClO 4 in glass beaker cell. The 20 khz ultrasonication to the water/oil mixture was conducted with an ultrasonic stepped horn (13 mm diameter, titanium alloy) connected with a 20 khz oscillator (44 W cm -2, SONIFIER-250D, Branson Ultrasonics Co.) for 5 min. The sequential ultrasonication with 1.6 MHz treatment after 20 khz was carried out using an ultrasonic transducer (16 W cm -2, Honda Electric Co.) connected with a Pyrex glass cylindrical tube (diameter, 24 mm; length, 75 mm) for 5 min. The further sequential ultrasonication with 2.4 MHz treatment after 20 khz and 1.6 MHz was conducted by an ultrasonic transducer (7 W cm -2, Honda Electric Co.) connected with a Pyrex glass cylindrical tube (diameter, 24 mm; length, 75 mm) for 5 min. 3. Photographic recording of EDOT emulsion The appearance of the EDOT emulsion was monitored with photographic recording. The photographs were taken with a digital camera (IXY 300, Cannon Co.). S1

2 4. Measurement of droplet size and distribution Droplet size distribution was determined by the dynamic light scattering method at 25 C with light scattering photometer (nano-zs ZEN 3600, Sysmex Co.) without diluting the mixture. The minimal measurement time of 10 min was required for setting and stabilizing of the sample before the first data points were obtained. 5. Electropolymerization of EDOT The polymerization of EDOT was carried out by a constant potential method under the following electrolytic conditions: Working electrode, glass plate coated with indium tin oxide (1 x 3 cm 2 ); counter electrode; platinum plate (2 x 2 cm 2 ); reference electrode, saturated calomel electrode (SCE); electrochemical cell, undivided glass beaker cell; temperature, 25±2 o C; applied potential, +1.4 V vs. SCE; EDOT monomer, 0.5 mmol; electrolytes, 1.0 M lithium perchlorate in water. 6. Scanning Electron Microscopy (SEM) After the polymerization, the PEDOT film deposited on the working electrode was washed with acetonitrile to remove the monomer remaining in the film, and then dried under reduced pressure. After this process, the surface morphology of the films was observed by SEM (VE-7800, Keyence Co.). The accelerating voltage of SEM was 15 kv. 7. Measurement of electrical conductivity (four-probe method) After the polymerization, the PEDOT film deposited on the working electrode was washed with acetonitrile to remove the monomer remaining in the film, and then dried under reduced pressure. After this process, the film was removed from the working electrode and the obtained free-standing film was subjected to electrical conductivity measurement (Model 1116SLD, Husou Electrochemical System Co.). The thickness of film was also measured by laser focus displacement meter (LT-8010, KEYENCE Co.). 8. Measurement of transmittance spectrum After the polymerization, the PEDOT film deposited on the working electrode was washed with acetonitrile to remove the monomer remaining in the film, and then dried under reduced pressure. After this process, the film was removed from the working electrode and the obtained free-standing film was subjected to transmittance spectrum measurement (UV-1800, Shimadzu Co.). S2

3 9. Changes to the size distribution as a function of sonication time Appropriate sonication time length for each step in the tandem operation was estimated with the averaged droplet size of EDOT obtained from the size distribution. As shown in Figures S1, the average size decreased with an increase in 20 khz sonication time, and reached to 351 nm at 5 min. The mean size was little affected by sonication time of 5 min or above. On the other hand, as shown in Figure S2, sequential ultrasonication using 1.6 MHz after 20 khz ultrasonication for 5 min successfully broke up larger droplets into smaller droplets with an increasing the 1.6 MHz sonication time, and reached to 208 nm at 5 min sonication time. The mean size was not changed by further elongation of the sonication time. As shown in Figure S3, further sequential processing with 2.4 MHz after 20 khz ultrasonication for 5 min and 1.6 MHz ultrasonication for 5 min enabled a further reduction in droplet size, and the peak shifted to 82 nm at 5 min sonication time. The mean size was little changed by further elongation of the sonication time. Therefore, it can be stated that appropriate sonication time length for each step in the tandem operation is 5 min. Figure S1. Size distributions of EDOT droplets in acoustically emulsified aqueous solutions (0.02 M EDOT, 1.0 M LiClO 4 ). Emulsification conditions were (a) 20 khz, 1 min, (b) 20 khz, 3 min, (c) 20 khz, 5 min, and (d) 20 khz, 7 min. S3

4 Figure S2. Size distributions of EDOT droplets in acoustically emulsified aqueous solutions (0.02 M EDOT, 1.0 M LiClO 4 ). Emulsification conditions were (a) 20 khz, 5 min 1.6 MHz, 1 min, (b) 20 khz, 5 min 1.6 MHz, 3 min, (c) 20 khz, 5 min 1.6 MHz, 5 min, and (d) 20 khz, 5 min 1.6 MHz, 7 min. Figure S3. Size distributions of EDOT droplets in acoustically emulsified aqueous solutions (0.02 M EDOT, 1.0 M LiClO 4 ). Emulsification conditions were (a) 20 khz, 5 min 1.6 MHz, 5 min 2.4 MHz, 1 min., (b) 20 khz, 5 min 1.6 MHz, 5 min 2.4 MHz, 3 min., (c) 20 khz, 5 min 1.6 MHz, 5 min 2.4 MHz, 5 min., and (d) 20 khz, 5 min 1.6 MHz, 5 min 2.4 MHz, 7 min. S4

5 10. Stability of the emulsions formed in the absence and presence of a stabilizing surfactant during the sonication steps Stability of the emulsions formed in the absence and presence of a stabilizing surfactant (0.1 M sodium dodecyl sulfate) during the sonication steps was estimated with the droplet size and its change with standing time after ultrasonic treatments. As shown in Figure S4, the size of EDOT droplets increased with an increasing the standing time after 20 khz ultrasonication for 5 min, and reached to ca nm at 60 min of the standing time. On the other hand, the droplets formed after two-step sonication at 20 khz (5 min) 1.6 MHz (5 min) and three-step sonication at 20 khz (5 min) 1.6 MHz (5 min) 2.4 MHz (5 min) were highly stable so that the coalesence was hardly observed even for 60 min. On the other hand, as shown in Figure S5, the use of a stabilizing surfactant resulted in the formation of highly stable emulsion droplets with diameters of a few tens of nanometers and their sizes were found to be little affected by ultrasonic treatments. Probably the emulsion droplet size was determined by the micelle size in this case. Figure S4. Temporal changes in mean size of EDOT droplets formed by acoustic emulsification in the absence of surfactant. Emulsification conditions were (a) 20 khz, 5 min, (b) 20 khz, 5 min 1.6 MHz, 5 min, and (c) 20 khz, 5 min 1.6 MHz, 5 min 2.4 MHz, 5 min. S5

6 Figure S5. Temporal changes in mean size of EDOT droplets formed by acoustic emulsification in the presence of surfactant (0.1 M sodium dodecyl sulfate). Emulsification conditions were (a) 20 khz, 5 min, (b) 20 khz, 5 min 1.6 MHz, 5 min, and (c) 20 khz, 5 min 1.6 MHz, 5 min 2.4 MHz, 5 min. 11. Tandem acoustic emulsification for preparation of other clear and transparent oil-in-water emulsion and water-in-oil emulsion Not only of another oil (methylmethacrylate)-in-water emulsion with clear and transparent appearance but also of clear and transparent water-in-oil (chloroform) emulsion could be obtained by the tandem acoustic emulsification. Figure S6. Photographs of the tandem acoustic emulsification treatment of methylmethacrylate (MMA) in water. Volume ratio of MMA to water, 1:10. (a) Original MMA-in-water mixture. Emulsification after (b) 20 khz, 8 min and (c) 20 khz, 8 min 1.6 MHz, 10 min 2.4 MHz, 10 min treatments. S6

7 Figure S7. Photographs of the tandem acoustic emulsification treatment of water (50% NaOHaq.) in chloroform. Volume ratio of water (50% NaOHaq.) to chloroform, 1:6. (a) Original water-in-chloroform mixture. Emulsification after (b) 20 khz, 15 min and (c) 20 khz, 15 min 1.6 MHz, 5 min 2.4 MHz, 5 min treatments. S7