Supporting Information

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1 Supporting Information Azo Polymer Janus Particles and Their Photoinduced Symmetry-Breaking Deformation Xinran Zhou, Yi Du, Xiaogong Wang* Department of Chemical Engineering, Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing , People s Republic of China

2 1. Materials N-Ethyl-N-ethanolaniline, methacryloyl chloride, hydroxyethyl methacrylate, triethylamine, adamantane-1-carbonyl chloride and 4-aminobenzonitrile were purchased from the commercial sources and used without further purification. The monomers, 2-(N-ethyl-N-phenylamino)ethyl methacrylate was synthesized through a literature method reported in our previous paper. 1 Concentrated sulphuric acid and glacial acetic acid were purchased and used for the post-polymerization azo-coupling reactions. Chromatographically pure tetrahydrofuran (THF) and analytical pure N, N-dimethylformamide (DMF) and dichloromethane (DCM) were used as the solvents, which were purchased from commercial sources and used as received. Low molecular weight poly(vinyl alcohol) (PVA) from Alfa Aesar with an alcoholysis degree of 86%-89% was adopted as the surfactant. Poly(methyl mathacrylate) (PMMA) with weight-average molecular weight of 350 k was obtained from the commercial source to be used to prepare the Janus particles (JPs). Ultrapure water (resistivity > 18.0 MΩ cm) was supplied by a Milli-Q water purification system and used for all experiments. 2. Synthesis of PAZO-ADMA Polymer PAZO-ADMA was synthesized through the following route, 2 which is described below in detail. a) PAN-HEMA The precursor polymer was obtained by copolymerization of 2-(N-ethyl-N-phenylamino)ethyl methacrylate and hydroxyethyl methacrylate through radical polymerization. Hydroxyethyl methacrylate (HEMA, 62.0 mg, mmol) and 2-(N-ethyl-N-phenyl)amino)ethyl methacrylate (EPAEMA, 1.0 g, 4.29 mmol) with a molar ratio of 1:9 were dissolved in anisole to reach a concentration of 25%. The polymerization initiated with azobisisobutyronitrile (AIBN, 10.6 mg, 1 wt%) was carried out at 70 C for 24 h. After that, the polymer solution was diluted, precipitated in petroleum ether and collected by filtration. Then, the polymer was redissolved in THF and precipitated in petroleum ether again to remove the residual monomers. The copolymer was dried in vacuum oven under 70 C for 12 h before further experiment and characterization. 1 H-NMR (600 MHz, CDCl 3, δ): 7.16 (s, 1.8H, m-ar H), 6.69 (s,

3 1.8H, o-ar H), 6.63 (s, 0.9H, p-ar H), 4.03 (br, 1.8H, CH 2 ), 3.99 (br, 0.2H, CH 2 ), 3.75 (br, 0.2H, CH 2 ), 3.49 (br, 1.8H, CH 2 ), 3.32 (br, 1.8H, CH 2 ), (br, 2H, CH 2 ), 1.12 (br, 2.7H, CH 3 ), 0.83 (br, 3H, CH 3 ). GPC: M n = , PDI=3.47. b) PAN-ADMA PAN-HEMA (1.01 g) and triethylamine (0.195 g, 1.91 mmol) were dissolved in THF (200 ml). Adamantane-1-carbonyl chloride (0.379 g, 1.91 mmol) was dissolved in THF (50 ml) and added dropwise into the polymer solution with ice-bath cooling. After 24 h, the mixture was filtered to remove triethylamine salt and the filtrate was precipitated in petroleum ether to remove the extra triethylamine and adamantane-1-carbonyl chloride. The precipitate was washed with petroleum ether and dried in vacuum oven under 70 C for 12 h before further experiment and characterization. 1 H-NMR (600 MHz, DMSO-d 6, δ): 7.06 (s, 1.8H, m-ar H), 6.63 (s, 1.8H, o-ar H), 6.51 (s, 0.9H, p-ar H), 3.89 (br, 2.2H, CH 2, overlapped), 3.38 (br, 1.8H, CH 2, overlapped), 3.25 (br, 1.8H, CH 2, overlapped), (br, 2H, CH 2 ), (1.5H, CH 2, CH, overlapped), 0.96 (br, 2.7H,CH 3 ), (br, 3H, CH 3 ). c) PAZO-ADMA PAN-ADMA (1.09 g) was dissolved in DMF (300 ml) and stirred with ice-bath cooling. The diazonium salt was prepared by adding an aqueous solution of sodium nitrite (0.53 g, 7.72 mmol in 3 ml of water) into a solution of 4-aminobenzonitrile (0.78 g, 6.43 mmol) in a homogeneous mixture of sulfuric acid (2 ml) and glacial acetic acid (20 ml). The mixture was stirred at 0 C for 1 min and then added dropwise into the PAN-ADMA solution. The solution was stirred at 0 C for 12 h to complete the reaction. Then, the solution was poured into plenty of water and the precipitate was collected and dried. The product was dissolved in THF (40 ml) and precipitated into petroleum ether (400 ml). The precipitate was washed with petroleum ether and dried in vacuum oven under 70 C for 12 h before further experiment and characterization. 1 H-NMR (600 MHz, DMSO-d 6, δ): 7.62 (br, 5.4H, Ar H, overlapped), 6.66 (br, 1.8H, Ar H), 3.98 (br, 2.2H, CH 2, overlapped), 3.48 (br, 3.6H, CH 2, overlapped), (br, 2H, CH 2 ), (1.5H, CH 2, CH, overlapped), 0.94 (br, 3H, CH 3 ), (br, 3H, CH 3 ). The 1 H-NMR spectra of the precursor polymers and target polymers, GPC curves, DSC curves, TGA results, UV-vis spectra and IR spectrum can be seen in our previous article Janus Particle (JP) Fabrication PAZO-ADMA and PMMA were dissolved in DCM to form a solution of 10.0 mg/ml for each polymer and a PVA aqueous solution of 2.5 wt% was also prepared. After that, the polymer solution (2 ml) was added slowly under PVA solution (50 ml), with which moderate stirring was adopted to help disperse the DCM solution into small droplets. With DCM volatilizing, PAZO-ADMA and PMMA were solidified and phase separated to form JPs. Then, the suspension was centrifugally fractionated to collect JPs with diameters in 10 µm and 1 µm scales, respectively, and

4 the particles were washed to remove residual PVA. 4. Photoinduced Deformation Experiment The samples were prepared by dropping water suspensions of JPs onto glass slides, silicon wafers, and TEM grids as substrates, which were dried under the ambient condition for 24 h before the light irradiation. A beam of linearly polarized light from a semiconductor laser (488 nm, Genesis CX SLM, Coherent Corporation) was used as the light source, which was expanded with a spatial filter (pinhole, 25 µm). Then, an additional convex lens was adopted to generate a parallel homogeneous spot with a diameter of 20 mm, after that, a diaphragm with a diameter of 6 mm was used to pick the central part of the beam. An additional microscope objective was used to obtain a parallel homogeneous spot with a 3 mm diameter. The laser beam was adjusted to have an intensity of 100 mw/cm 2 or 200 mw/cm 2 according to the specific experimental conditions. The polarization direction of the laser beam was fixed to be horizontally parallel. All light irradiation experiments were carried out at room temperature under an air-ambient condition with normal incidence. 5. Characterization a) Instruments 1 H-NMR spectra were recorded on a JEOL JNM-ECA600 NMR spectrometer (600 MHz for proton) by using CDCl 3 or DMSO-d 6 as the solvents and tetramethylsilane as internal standard. The molecular weights and molecular weight distributions were measured by using a gel permeation chromatography (GPC) apparatus with THF as eluent (1 ml/min). The instrument was equipped with a refractive index (RI) detector (Wyatt Optilab rex) and fitted with a PL gel 5 µm mixed-d column. The measurements were carried out at 35 C and the data was calibrated with linear polystyrene standards. Thermal transition behavior of the polymers was characterized by using TA Instruments DSC 2920 with a heating rate of 10 C/min in nitrogen atmosphere. Thermal gravimetric analysis (TGA) was performed with a TA Instruments TGA 2050 thermogravimetric analyzer at a heating rate of 10 C/min from room temperature to 800 C under a continuous flow of nitrogen. Infrared spectra were determined using a Nicolet 560-IR FT-IR spectrophotometer by incorporating samples in KBr disks. UV-vis absorption spectra were recorded by a Perkin-Elmer Lamba Bio-40 spectrophotometer. An optical microscope with oil immersion lens (X100) from Olympus (IX 81) was used to obtain the images from direct observation. A scanning electron microscope (SEM) apparatus from Zeiss Corporation (Zeiss Merlin) was used to characterize the morphological properties before and after the light irradiation, with which an EDS apparatus was used to acquire the surface element content. A high vacuum ( mbar, approximately) condition was adopted while the accelerating voltage and current were 5 kv and 100 pa respectively. A transmission electron microscope (TEM, H-7650B, HITACHI) was used to acquire the images of shape variation with an accelerating voltage of 80 kv. The details of characterization could be viewed as the following.

5 b) Microscopic Observations An optical microscope from Olympus (IX81) with a CCD apparatus was used to acquire the images of azo polymer JPs in 10 µm scale before and after the light irradiation, during which an oil immersion lens (X100) was adopted to get clear images. A transmission electron microscope (TEM, H-7650B, HITACHI) was used to acquire the images of profile variation with an accelerating voltage of 80 kv. For TEM sample preparation, drops of JPs suspension were added onto a copper grid coated with carbon film and then dried under room temperature for 24 h. A scanning electron microscope (SEM) apparatus from Zeiss Corporation (Zeiss Merlin) was used to characterize the morphological properties before and after irradiation, with which a EDS apparatus was used to acquire the surface element content. For SEM sample preparation, drops of JPs suspension were added onto a clean piece of silicon wafer and then dried under room temperature for 24 h, after which a layer of carbon in thickness of several nanometer was coated onto the surface to enhance the conductivity. 6. OM Images of JPs with different PAZO-ADMA/PMMA ratios The JPs were obtained by using the solutions with the different PAZO-ADMA and PMMA ratios. The total concentration of the polymers in DCM was 20 mg/ml. Figure S1. PAZO-ADMA/PMMA = 1:2 (wt/wt). Figure S2. PAZO-ADMA/PMMA = 1:4 (wt/wt).

6 Figure S3. PAZO-ADMA/PMMA = 2:1 (wt/wt). Figure S4. PAZO-ADMA/PMMA = 4:1 (wt/wt). References 1. Wang, D. R.; Ren, H. F.; Wang, X. L.; Wang, X. G. Macromolecules 2008, 41, Zhou, X. R.; Du, Y.; Wang, X. G. Macromol. Chem. Phys. 2015, DOI: /macp