Supporting Information. Synthesis of ph-responsive Inorganic Janus. Nanoparticles and Experimental Investigation of the

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1 Supporting Information Synthesis of ph-responsive Inorganic Janus Nanoparticles and Experimental Investigation of the Stability of Their Pickering Emulsions Wei Xue,, Hengquan Yang,*, and Zhiping Du*,# School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan , China China Research Institute of Daily Chemical Industry, Taiyuan , China # Institute of Resources and Environmental Engineering, Shanxi University, Taiyuan , China *Corresponding author: hqyang@sxu.edu.cn and duzhiping@sxu.edu.cn Experimental Section Scheme S1. Schematic representation illustrating the fabrication of interfacial active spherical Janus nanoparticles NH 2 -SiO 2 -C8 through Pickering emulsion process. Figure S1. TEM image of dense SiO 2 nanoparticles prepared by the modified Stöber method and the histogram of size distribution plot (inset). Figure S2. Optical photograph of wax-in-water Pickering emulsion and the histogram of size distribution plot (inset) of wax@ SiO 2 colloidosomes. Figure S3. SEM of a single wax@sio 2 colloidosomes. Figure S4. SEM of the surface arrays of SiO 2 nanoparticles at the interface of wax@sio 2 colloidosomes. Figure S5. Water contact angle of SiO 2 and its derivatives. Figure S6. Zeta potential of SiO 2 NH 2 nanoparticles.

2 Experimental Section Materials. Tetraethyl orthosilicate (TEOS, AR, 96%), ethanol absolute (AR, 99%), methanol (AR, 99%), ammonia water (NH 3 H 2 O, 25 wt %), toluene (AR, 99%), ethyl acetate (AR, 99%), diethyl ether (AR, 99%), n-octane (CP, 98%), dichloromethane (AR, 99%) and chloroform (AR, 99%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Trimethoxysilylpropyldiethylenetriamine (triamine, 95%) and n-octyltrimethoxysilane (n-otms, 97%) were obtained from Beijing J&K Scientific Ltd. (China). Paraffin wax (melting point o C) was purchased from Shanghai Huashen Recover Equipment Co., Ltd. Didodecyldimethylammonium bromide (DDAB, 98%), n-dodecane (AR, 99%), NaBH 4 and triethylamine (TEA, 99%) were obtained from Aladdin Industrial Corp. (Shanghai, China). Nile Red (CAS No ) was obtained from Sigma-Aldrich. Deionized water was used in all experiments without further purification. Preparation of SiO 2 Nanoparticles. 1 The SiO 2 nanoparticles were synthesized on the basis of the well-established Stöber method with minor modification. Briefly, 200 ml ethanol absolute, 12.2 ml water and 16.0 ml ammonia water were mixed together in a 250 ml bounded-flask under vigorous stirring for 30 min at 25 o C, and then 12.4 ml TEOS was dropwise added into the mixture. After further stirring at 25 o C for 12 hours, the precipitation was isolated by filtration followed by washing repeatedly with water. The SiO 2 nanoparticles were obtained after dried at 105 o C under air for 4 hours. Before using, SiO 2 nanoparticles were sieved with 100 mesh sieves and then pretreated with Piranha solution so as to activate hydroxyl group at the interface thoroughly. Preparation of NH 2 -SiO 2 -C8 Janus Nanoparticles (JNPs) Modified with Triamine and n-otms. Preparation of wax@sio 2 colloidosomes. The preparation of NH 2 -SiO 2 -C8 Janus nanoparticles was received according to a wax-in-water Pickering emulsion. 2-5 Briefly, SiO 2 nanoparticles 0.5 g and paraffin wax 5.0 g were successively added into 20 ml DDAB aqueous solution with a concentration of 60 mg L -1. After incubated at 80 o C for 30 minutes, the resulting mixture was stirring vigorously with homogenizer (SCIENTZ-XHF-DY, 10 mm dispersing tool) at rpm for 2 minutes followed by 1500 rpm for 2 minutes at 80 o C to prevent further flocculation. After cooling down to ambient temperature, the as-obtained mixture was filtered and then washed with abundant water to remove SiO 2 nanoparticles attached weakly and free surfactant. The wax@sio 2 colloidosomes were obtained after natural drying at room temperature. Scheme S1. Schematic representation illustrating the fabrication of interfacial active spherical Janus nanoparticles NH 2 -SiO 2 -C8 through Pickering emulsion process. SiO 2 -NH 2 Janus nanoparticles. About 11 g of as-prepared wax@sio 2 colloidosomes (containing SiO 2 ~ 1 g) was added into the mixture of 0.3 mmol triamine and 20 ml methanol, and then the above S1

3 mixture was rotated gently overnight under ambient temperature after dispersed homogenously by shaking gently. The precipitation was collected after centrifugation and then washed 3 times, 5 times, and twice with methanol, chloroform, and methanol, respectively. The SiO 2 -NH 2 were obtained after dried at 50 o C under vacuum for 4 hours. NH 2 -SiO 2 -C8 Janus nanoparticles. About 1.0 g of the above material was added into the mixture of 1.0 mmol n-otms and 3.3 mmol TEA in 5 ml toluene, and then refluxing 4 hours with high speed stirring under N 2 atmosphere after dispersed homogenously by ultrasonic. The supernatant was discarded after centrifugation and the precipitation was washed 5 times and twice with toluene and methanol, respectively. Finally, the Janus nanoparticles were received after dried at 50 o C under vacuum for 4 hours. NH 2 -C8 Bi-Functionalized SiO 2 Nanoparticles (NH 2 /SiO 2 /C8 HNPs). 6 A mixture of 0.06 mmol triamine, 1.44 mmol n-otms and 5 mmol TEA were successively added into 5 ml toluene, and then 1.0 g SiO 2 nanoparticles were added into the solution followed by dispersed homogenously by ultrasonic. After refluxing with rapid stirring for 4 h under N 2 atmosphere, the NH 2 /SiO 2 /C8 HNPs nanoparticles were obtained by centrifugation and washed five times with toluene and dried at 80 o C under vacuum for 4 hours subsequently. NH 2 -Functionalized SiO 2 (SiO 2 -NH 2 ) Nanoparticles. 6 SiO 2 -NH 2 nanoparticles were synthesized according to Yang after minor modification. Triamine of 0.3 mmol was added into 5 ml toluene, and then 1.0 g SiO 2 nanoparticles were added into the above solution followed by dispersed homogenously by ultrasonic. After refluxing with rapid stirring for 4 h under N 2 atmosphere, the SiO 2 -NH 2 nanoparticles were obtained by centrifugation and washed five times with toluene and twice with methanol and dried at 50 o C under vacuum for 4 hours subsequently. C8 Functionalized SiO 2 (SiO 2 -C8) Nanoparticles. 6 SiO 2 -C8 nanoparticles were synthesized according to Yang after minor modification. A mixture of 1.0 mmol n-otms and 3.3 mmol TEA were successively added into 5 ml toluene, and then 1.0 g SiO 2 nanoparticles were added into the solution followed by dispersed homogenously by ultrasonic. After refluxing with rapid stirring for 4 h under N 2 atmosphere, the SiO 2 -C8 nanoparticles were obtained by centrifugation and washed five times with toluene and twice with methanol and dried at 50 o C under vacuum for 4 hours subsequently. Loading Au Nanoparticles onto the Surface of NH 2 -SiO 2 -C8 Janus Nanoparticles. About 0.1 g NH 2 -SiO 2 -C8 Janus Nanoparticles were added into 1.7 ml HAuCl 4 aqueous solution (2.9 mmol L -1 ). After stirring for 4 hours at ambient temperature, the mixture was isolated via centrifugation. The amount of HAuCl 4 adsorbed onto the surface of NH 2 -SiO 2 -C8 can be quantified by UV-Vis through monitoring the absorbance of the solution before and after adsorption. The Au-adsorbed particles was further reduced with NaBH 4 in a mixture of toluene and ethanol (V/V = 20:1). After stirring for 4 h, the solid was isolated through centrifugation and washed four times with ethanol. After being dried under vacuum, the NH 2 -SiO 2 -C8 Janus nanoparticles labeled with Au nanoparticles were received. Preparation of Pickering Emulsions. For synthesis of Janus nanoparticles, wax-in-water Pickering emulsion was prepared with a high speed homogenizer as aforementioned. For interfacial activity S2

4 and stability tests, a typical procedure to prepare Pickering emulsion was as follows: a certain volume of oil phase (usually with n-dodecane except interfacial activity experiment with a wide range of organic solvents) was injected into a vial with a certain amount of solid emulsifier followed by sonication 5 minutes in order to make it dispersed thoroughly. Then, a certain volume of water was added into the vial. The oil-water volume ratio was 1:1 and the nanoparticle concentration was fixed to 1.0 wt % relative to the mass of water. After hand-shaking fiercely 1 minute, the Pickering emulsion stabilized by nanoparticles was obtained. Stability of Pickering Emulsion. The stability of the Pickering emulsion was evaluated by centrifugation method based on phase separation phenomenon. The stability was tested with a centrifugal machine HC-2066 from ZONKIA under different angular velocity. The centrifugation time was fixed to 1 minute, the size of centrifuge tube size was 80 mm * φ 14 mm, and the tube volume was 10 ml. The radius between axis and centrifuge tube was 7.5 cm. The Pickering emulsion in a sealed tube was standing statically overnight to let it sedimentation naturally before centrifugation tests. Characterization. The powder samples were placed on carbon tape for Scanning electron microscope (SEM) measurements with JSM Transmission electron microscope (TEM) images were obtained on a JEM-2000EX (operated at 200 kv). Thermogravimetric analysis (TGA) was performed on TA Q600 Instruments. All dried powder samples were heated from 30 o C to 900 o C at a rate of 10 o C min -1 under air atmosphere environment with a flow rate of 10 ml min -1. C and N content analysis was conducted on Vario EL (Elementar). X-ray photoelectron spectra (XPS) were recorded on a Kratos Axis Ultra DLD, and the C1S line at ev was used as a reference. UV-Vis determination was conducted on a TU-1900 spectrometer (China). The water contact angles in air on sample disks were measured using a Krüss DSA100 instrument. Before measurement, the powder sample was compressed into a disk with a thickness of approximately 1 mm under 1 MPa for 2 minutes by a tablet press machine. A drop of water (1 μl) was injected on the sample disk. The appearance of the water drop was recorded at ca. 0.1 s with a digital camera. The contact angle was determined by a photogoniometric method. Zeta potential measurements were conducted as a function of ph using a Malvern Zetasizer Nano-ZS under room temperature. The concentration of suspension was set as 0.1 w/v %. The ph value of the solution for formulating the suspension was adjusted using HCl solution (1 mol L -1 ) or NaOH solution (1 mol L -1 ) and measured with a ph meter (Mettler Toledo, FE20K). Prior to measurements, the suspension was treated with ultrasound for 5 min. Every point was tested 3 times and the average value is taken. Emulsion droplets were observed using an optical microscope (XSP-8CA, Shanghai, China) equipped with 4 or 10 magnification lens. Confocal laser scanning microscopy images were obtained on a Carl Zeiss LSM880 instrument (Germany). The concentration of Nile Red in toluene was M and the excitation wavelength is 559 nm (red). Calculation of surface coverage. The average droplet size was estimated based on 200 droplets. If we assume the following: (1) all of the particles added to the system are irreversibly adsorbed at the oil-water interface, 7 (2) the particles are spherical and uniform, 8 (3) the emulsion droplets are also spherical and monodisperse, 9 (4) the average diameter of the particles is much smaller than that of S3

5 the emulsion droplets, 10 (5) the contact angle of particle at the oil-water interface is 90 o, 10 and (6) the particles at the oil-water interface form a close-packed monolayer, 8 the relationship among the surface coverage, the size of emulsion droplets and the diameter of adsorbent materials can be rationalized in terms of the following equation: 11 = (S1) Where, C is the surface coverage of the emulsion, D is the average size of emulsion droplets, m p is the mass of solid particle emulsifier, ρ p is the density of the solid particle emulsifier (2.65 g cm -3 for dense SiO 2 nanoparticles 12,13 ), V d is the volume of the dispersed phase, and d p is the average diameter of solid particle emulsifier. Here, the wax was added in solid state and the density of wax was approximately employed as 0.9 g cm -3. Assuming that it is obedient to the hypothetical model perfectly, the theoretical value of C is 0.9; when C < 0.9, the adsorbent materials at the interface packed relative loosely than the ideal; when C > 0.9, the excess adsorbent materials would start to take the manner of multilayer adsorbed with the increasing of C or free dispersed into continuous phase. 14 S4

6 Figure S1. TEM image of dense SiO 2 nanoparticles prepared by the modified Stöber method and the histogram of size distribution plot (inset). S5

7 Figure S2. Optical photograph of wax-in-water Pickering emulsion and the histogram of size distribution plot (inset) of 2 colloidosomes. The emulsion composition consists of 0.5 g SiO 2 nanoparticles, 5.0 g paraffin wax and 20 ml DDAB aqueous solution (60 mg L -1 ). S6

8 Figure S3. SEM of a single wax@sio 2 colloidosomes. S7

9 Figure S4. SEM of the surface arrays of SiO 2 nanoparticles at the interface of wax@sio 2 colloidosomes. S8

10 Figure S5. Water contact angle of SiO 2 and its derivatives. S9

11 60 Zeta potential (mv) SiO 2 -NH ph Figure S6. Zeta potential of SiO 2 NH 2 nanoparticles. S10

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