Supporting Information

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1 Supporting Information Amphiphilic Layer-by-Layer Assembly Overcoming Solvent Polarity between Aqueous and Nonpolar Media Minkyung Park, Younghoon Kim, Yongmin Ko, Sanghyuk Cheong, Sook Won Ryu, and Jinhan Cho* Experimental Details Materials: Poly(4-sodium, styrenesulfonic acid) (PSS) (M w = , Aldrich) of 1 mg ml -1 in aqueous solution were used as an anionic polyelectrolyte. OA Ag, [S1] OA Fe 3 O 4, [S2,S3] OA MnO, [S4] OA TiO 2 NPs, [S5] rgo SO 3, [S6,S7] + and rgo NH [S8] 3 were prepared as previously reported by other + research groups. In the case of rgo NH 3 nanosheets, which were synthesized standing upon the previously reported research, however GO nanosheets were used instead of oxidized-multiwall + carbon nanotube (MWCNT COOH) and resulting GO NH 3 nanosheets were reduced using hydrazine. For the preparation of anionic octakis Fe 3 O 4 NP dispersions, the OA-Fe 3 O 4 NPs (10 mg ml 1 ) were transferred from toluene to aqueous media using water-dispersible octakis (10 mmol, the same concentration as that of OA for ligand exchange). For the preparation of cationic Fe 3 O 4 NPs (10 mg ml 1 ), the OA-Fe 3 O 4 NP toluene solution (10 mg ml 1 ) of 20 ml was first mixed with aqueous solution containing ethylene diamine (20 mg ml 1, Fluka). After sufficient mixing process, excess acetone was added to the mixed solution for the precipitation of ethylene diamine-stabilized Fe 3 O 4 NPs. These precipitates were re-dispersed in ph 9 water after dialysis process. The resulting NPs are cationic Fe 3 O 4 NPs (i.e., Fe 3 O 4 NH + 3 NPs). Build-up of (PSS/hydrophobic NP) n Multilayers: (1) Flat substrate: A toluene solution of hydrophobic NPs (i.e., OA-Ag, OA-Fe 3 O 4, OA-MnO, OA-TiO 2 ) stabilized by oleic acid and aqueous solutions of PSS (M w = , Aldrich) and poly(allylamine hydrochloride) (PAH, M w = , Aldrich) were prepared at concentrations of 10, 1, and 1 mg ml 1, respectively. In this case, 0.2 M NaCl ionic salts were added to the PSS (ph = 6.0) and PAH (ph = 4.2) solutions. For the build-up of LbL assembled multilayer, the quartz or silicon substrates were first cleaned with an RCA solution (H 2 O/NH 3 /H 2 O 2 5:1:1 v/v/v) at 60 o C. The resulting negatively charged substrates were first dipped into the positively charged PAH (M w = , Aldrich) for 10 min, washed twice with deionized water, and dried sufficiently under a gentle nitrogen stream. The PAH-coated substrates were dipped into a PSS solution for 10 min, followed by washing with deionized water and thorough drying with nitrogen. The PSS-coated substrate was dip into the hydrophobic NP S1

2 solution for 30 min, followed by washing with toluene and drying with N 2 gas. After that, the substrates were dipped into the PSS solution for 10 min, again. These dipping cycles were repeated until the desired number of layers had been obtained. (2) Colloidal substrate: For the build-up of multilayers onto colloidal substrate, 100 L of a concentrated dispersion (6.4 wt%) of negatively charged 600 nm silica colloids was first diluted to 0.5 ml with deionized water. After rapid centrifugation of colloidal solution at 8000 rpm for 5min, supernatant water was removed, and then PAH aqueous solution of 1 mg.ml -1 was added to silica colloidal sediment followed by ultra-sonication and sufficient adsorption time. Excess PAH was eliminated by two-time centrifugation (6000 rpm, 5 min)/wash cycles. For the preparation of multilayers onto cationic PAH-silica colloids, anionic PSS aqueous solution of 1 mg.ml -1 was added to cationic silica colloids, again. The adsorption and washing cycle of PSS were exactly same as those of abovementioned PAH. After that, 0.5 ml of OA Fe 3 O 4 NPs (1 mg ml 1 ) in toluene was added to the outermost PSS layer-coated silica colloids and after deposition during 10 min, the excess OA Fe 3 O 4 NPs was removed by two-time centrifugation as mentioned above. 0.5 ml of PSS (1 mg ml 1 ) in water was then deposited onto the OA Fe 3 O 4 NP-coated colloids using the same conditions. It should be noted that the adsorption process of functional components onto the colloidal substrates need no drying process. The above process was repeated until the desired layer number was deposited on the colloidal silica. Magnetism Measurements: The magnetism measurements of (PSS/OA-Fe 3 O 4 NP)n nanocomposite multilayers were investigated using a SQUID magnetometer (MPMS5). In this case, the multilayers exhibited the superparamagnetic properties, displaying the reversible magnetization curves without coercivity, remanence, or hysteresis at room temperature (see Supporting Information, Figure S6). [S9-S12] However, at liquid helium temperature (T = 5 K), the thermally activated magnetization flipping properties of the (PSS/OA Fe 3 O 4 ) n nanocomposite films showed frustrated superparamagnetic properties. UV-vis Spectroscopy: UV-vis spectra of dendrimer/hydrophobic NP multilayers on quartz glass were collected with a Perkin Elmer Lambda 35 UV-vis spectrometer. Quartz Crystal Microgravimetry (QCM) Measurements: A QCM device (QCM200, SRS) was used to examine the mass of the material deposited after each adsorption step. The resonance frequency of the QCM electrodes was approximately 5 MHz. For preparing PSS/OA Fe3O4 NP multilayers onto QCM electrode, 0.2 M NaCl PAH layer was first deposited onto QCM electrode. S2

3 After that, the adsorbed mass of PSS and OA-Fe 3 O 4 NPs, Δm, was calculated from the change in QCM frequency, ΔF, using the Sauerbrey equation [S13] : 2 2F0 F( Hz) A q q m Here, F 0 (~ 5 MHz) is the fundamental resonance frequency of the crystal, A is the electrode area, and ρ q, (~ 2.65 g cm 2 ) and q (~ 2.95 x g cm 2 s 2 ) are the shear modulus and density of quartz, respectively. This equation can be simplified as follows: ΔF (Hz) = 56.6 x Δm A, where Δm A is the mass change per quartz crystal unit area in g cm 2. In this case, we measured the ΔF per layer repeatedly (10 times), and the resultant standard deviation of the ΔF was obtained from the same layer. Packing density of OA-Fe 3 O 4 NPs onto polyelectrolyte layer: the 3D packing density of 8.6 nm OA-Fe 3 O 4 NPs adsorbed onto 0.2 M NaCl PSS layers (1 mg ml 1 ) was first calculated using the volume size (~ 3.33 x cm 3 ), the mass density (~ 5 g cm 3 ) of a single OA Fe 3 O 4 NP and the number density per unit area (~ 1.34 x cm 2 ) of the OA Fe 3 O 4 NP array. In this case, the mass of OA ligands bound to the surface of a single Fe 3 O 4 NP was considered negligible compared to that of Fe 3 O 4 NP, and the bottom surface of the Fe 3 O 4 NPs adsorbed onto the PSS sublayer was considered to not have any OA ligands due to the higher affinity of the SO 3 groups of PSS for the surface of the Fe 3 O 4 NPs. Therefore, we assumed that the mass density of OA Fe 3 O 4 NP is identical to that of bulk Fe 3 O 4. Based on this information, the volume occupied by OA Fe 3 O 4 NPs in an imaginary box with a volume size of 8.60 x 10-7 cm 3 (height of 8.60 nm and unit area of 1 x 1 cm 2 ) was calculated to be 4.46 x 10 7 cm 3. As a result, the 3D packing density of OA Fe 3 O 4 NPs per layer was approximately 52% (i.e., 4.46/8.60). The 2D packing density of OA Fe 3 O 4 NPs per layer was also calculated using the cross-sectional area (~ 5.81 x cm 2 ) of a single NP and the number density (~ 1.34 x cm 2 ) of OA-Fe 3 O 4 NPs per unit area. Therefore, the total area occupied by OA-Fe 3 O 4 NPs per unit area (~ 1 cm 2 ) was calculated to be approximately cm 2, which corresponds to the 2D packing density of 77.8%. Fourier Transform Infrared Spectroscopy (FTIR): Vibrational spectra were measured by FTIR spectroscopy (is10 FTIR, Thermo Fisher) in the transmission and attenuated total reflection (ATR) modes. The sample chamber was purged with N 2 gas for 2 h to eliminate water and CO 2 prior to conducting the FTIR measurement. An ATR-FTIR spectrum for the (PSS/hydrophobic NP) n film deposited onto a Au-coated substrate was obtained from 300 scans with an incident angle of 80. S3

4 The acquired raw data was plotted after baseline correction, and the spectrum was smoothed using spectrum analyzing software (OMNIC, Nicolet). Dynamic Light Scattering (DLS) : The hydrodynamic size of (PSS/OA-Fe 3 O 4 NP) n multilayercoated SiO 2 colloids was measured under dilute conditions using dynamic light scattering (DLS) (Zeta-potential & Particle size Analyzer ELSZ, OTSUKA ELECTRONICS CO.LTD)). The wavelength used was 633 nm with a scattering angle of 165. All experiments were done at 20 C Electrochemical Measurements: Electrochemical test of the (PSS/OA Fe 3 O 4 ) n multilayers deposited onto the PAH-coated indium tin oxide (ITO) electrode was measured at a three-electrode cell, using a Ag/AgCl electrode and Pt wire as the reference and counter electrodes, respectively. The LbL assembled (PSS/OA Fe 3 O 4 ) n electrode was employed as a working electrode in 0.1 M Na 2 SO 3 electrolyte solution. Cyclic voltammetry was performed in the potential range from 0.9 to V at scan rates of mv s -1. Electrochemical impedance spectroscopy (EIS) measurements were carried out by applying an AC voltage of 50 mv amplitude in the frequency range of 100 khz 0.1 Hz at room temperature. S4

5 Figure S1. ATR-FTIR spectra of PSS and OA-Fe 3 O 4 NPs. S5

6 Figure S2. UV-vis spectrum of (PSS/OA Fe 3 O 4 NP) n multilayers. In this case, the ionic strength and ph of PSS solution were adjusted to 0.2 M NaCl and 6, respectively. S6

7 (a) (b) (c) (d) Figure S3. UV-vis spectra of (a) (PVPA/OA Fe 3 O 4 NP) n, (b) (PVPA/OA TiO 2 NP) n, (c) (PVPA/OA Ag NP)n, and (d) (PVPA/OA MnO NP) n multilayers as a function of bilayer number (n). The insets indicate the UV-vis absorbance of (PVPA/hydrophobic NP) n multilayers as a function of bilayer number (n). S7

8 Figure S4. Frequency and mass change of the adsorbed PSS layer as a function of ionic strength of the PSS solution. In this case, the adsorption time of PSS was 10 min, and the concentrations of PSS solution was adjusted to be 1mg ml 1. S8

9 Figure S5. Absorbance (at 225 nm) dependence on the number of 0.2 M NaCl PSS/OA-Fe 3 O 4 NP bilayers with ph values of 3, 6, and 9. S9

10 (a) (b) (c) (d) Figure S6. (a)-(b) The magnetic curves of (PSS/OA Fe 3 O 4 NP) n=5,10 and 15 multilayers as a function of (a) bilayer number and (b) normalized magnetism per OA Fe 3 O 4 mass at 295 K. (c) The magnetic curves of (PSS/OA Fe 3 O 4 NP) n=5,10 and 15 multilayers measured at 5 K. (d) Temperature dependence of zero-field cooling (ZFC) and field cooling (FC) magnetization of isolated Fe 3 O 4 NPs and (PSS/OA Fe 3 O 4 NP) n=5,10 and 15 multilayers measured using 150 Oe. As shown in Figure S6a, the saturated magnetization increased regularly with increasing bilayer number (or the total amount of OA Fe 3 O 4 NP adsorbed within the multilayer films). The magnetization per gram of adsorbed nanoparticles was similar for different multilayered films and displayed a saturated magnetism of approximately 200 emu g -1 (Figure S6b). At liquid helium temperature (T = 5 K), the thermally activated magnetization flipping properties of the PSS/OA Fe 3 O 4 NP multilayers displayed the frustrated superparamagnetic properties (Figure S6c). The blocking temperature, which began to display some deviation between zero-field-cooling (ZFC) and field-cooling (FC) magnetization, was S10

11 fixed at approximately 60 K for both the isolated nanoparticles and multilayered films (Figure S6d). These results indicate that LbL multilayers maintain the unique and strong superparamagnetic properties of isolated OA Fe 3 O 4 NPs while avoiding the higher blocking temperature in the densely packed array induced by strong dipolar interactions. S11

12 Figure S7. Frequency and mass change of PVPA/OA-Fe 3 O 4 NP multilayers as a function of the layer number. The solution concentration of 0.5 M NaCl PVPA and OA-Fe 3 O 4 NP were adjusted to be 1 and 10 mg ml 1, respectively. In this case, the ΔF (or mass change, Δm) and the number density per unit area of the OA Fe 3 O 4 NP layer were measured to be 116 ± 5 Hz (Δm, ~ 2049 ng cm -2 ) and 1.19 x cm 2, respectively (calculation process is given in the experimental details of Supporting Information). Based on this information, 2D and 3D packing densities of OA-Fe 3 O 4 NPs onto PVPA layer were calculated to be approximately 69 and 46%, respectively. S12

13 Figure S8. Dispersion stability of anionic octakis Fe 3 O 4 NP in aqueous solution containing 0.1 M, 0.3 M, 0.5 M, 0.7 M NaCl, respectively. These NPs are immediately aggregated in aqueous solution with the ionic strength of above 0.3 M NaCl. S13

14 Figure S9. The size of (0.2 M NaCl PSS/OA Fe 3 O 4 NP) n=1,3, and 5 multilayer-coated colloids measured by DLS. The hydrodynamic size of (PSS/OA Fe 3 O 4 NP) n -coated colloids analyzed by DLS was apparently larger than the actual size denoted by SEM (see Figure 4b). S14

15 (a) (b) (c) (d) Figure S10. UV-vis spectra of (PSS/OA Fe 3 O 4 NP) n multilayers using OA-Fe 3 O 4 NPs dispersed in (a) toluene, (for comparison, Figure S2 is shown here again) (b) hexane, (c) THF, and (d) chloroform. The insets indicate the UV-vis absorbance of (PSS/ OA Fe 3 O 4 NP) n multilayers as a function of bilayer number (n). S15

16 (a) (b) (c) (d) Figure S11. UV-vis spectra of (a) (PEDOT:PSS/OA Fe 3 O 4 NP) n, (b) (PEDOT:PSS/OA TiO 2 NP) n, (c) (PEDOT:PSS/OA MnO NP) n, and (d) (PEDOT:PSS/OA Ag NP) n multilayers as a function of bilayer number (n). The insets indicate the UV-vis absorbance of (PEDOT:PSS/hydrophobic NP) n multilayers as a function of bilayer number (n). S16

17 (a) (b) (c) (d) Figure S12. UV-vis spectra of (a) (PSS/OA Ag NP) n, (b) (PSS/OA MnO NP) n, (c) (PSS/OA TiO 2 NP) n, and (d) (PSS/OA Fe 3 O 4 NP) n multilayers (for comparison, Figure S2 is shown here again). The insets indicate the UV-vis absorbance of (PSS/hydrophobic NP) n multilayers as a function of bilayer number (n). The ionic strength and ph of PSS solution were adjusted to 0.2 M NaCl and 6, respectively. Figure S12d redisplays the UV-vis spectra of (PSS/OA Fe 3 O 4 NP) n multilayers shown in Figure S2 for comparison. S17

18 Figure S13. D and G bands in the Raman spectra for GO and rgo SO 3. The bands at ~ 1590 and 1350 cm 1 in the Raman spectra are assigned to the G band (associated with the vibration of the sp 2 carbon atom in a graphitic 2D hexagonal lattice) and the D band (the vibrations of sp 3 carbon atoms of defects and disorder). The restoration of the -conjugation in rgo-so 3 compared to GO was investigated by Raman spectroscopy. The D (i.e., I(D)) and G band peak intensity (i.e., I(G)) ratio in the Raman spectrum is inversely proportional to the in-plane crystalline sizes. The I(D)/I(G) ratio of rgo-so 3 increased from 1.02 to As -conjugation systems formed from chemical reduction processes have smaller crystalline sizes (i.e., sp 2 carbon domain size), the increase of the I(D)/I(G) ratio is evidence of the restoration of the -conjugation. The weak and broad 2D peak at 2700 cm 1 is further evidence of disorder as a result of an out-of-plane vibrational mode, and the cooperation between the D and G peaks also induces an S3 peak near 2950 cm 1. After the reduction process, I(2D)/I(S3) is decreased. These results are similar to previous results reported by other research groups. [S6,S7,S14,S15] S18

19 Figure S14. Phase transfer of OA-Fe 3 O 4 NP from toluene to the aqueous solution containing rgo SO 3, (ratio of mass concentration of OA-Fe 3 O 4 NP and rgo SO 3 is 1: 1 or 2: 1), intermediate phase transfer of OA Fe 3 O 4 NP between toluene and aqueous media (OA-Fe 3 O 4 NP : rgo SO 3 is 5: 1 or 9: 1), and phase transfer of rgo SO 3 from aqueous media to toluene containing OA Fe 3 O 4 NPs (OA Fe 3 O 4 NP : rgo SO 3 = 10 : 1). HR-TEM images of the OA-Fe 3 O 4 -rgo SO 3 nanocomposites formed in aqueous (OA-Fe 3 O 4 : rgo SO 3 = 1 : 1), intermediate (5 : 1) and toluene phases (10 : 1). More specifically, the initial solution mixture containing rgo SO 3 and OA Fe 3 O 4 NPs was separated between the toluene phase with OA Fe 3 O 4 NPs and the water phase with rgo SO 3. However, in the case of the mixture containing the rgo SO 3 aqueous solution with a fixed concentration of 0.2 mg ml 1, the OA Fe 3 O 4 NPs at a concentration of 0.2 mg ml 1 were phasetransferred from toluene to the aqueous phase containing rgo SO 3 after vigorous stirring. In S19

20 contrast, the OA Fe 3 O 4 NP solution with a high concentration of 2.0 mg ml 1 strongly induced the phase transfer of rgo SO 3 from water to the toluene phase containing OA Fe 3 O 4 NPs. Additionally, these rgo nanocomposites were highly stable and dispersible in toluene phase without any additional surfactants. In the case of solutions containing intermediate concentrations of OA Fe 3 O 4 NPs (e.g., 1.0 mg ml 1 ), the nanocomposites composed of OA Fe 3 O 4 NPs and rgo SO 3 (e.g., OA Fe 3 O 4 rgo SO 3 ) were formed at the interface between the toluene and water phases. These results were confirmed by HR TEM images of rgo SO 3 /OA Fe 3 O 4 NP nanocomposites. It should also be noted that a variety of hydrophobic NPs instead of conventional small molecule-based organics operate as phase transfer agents for SO 3 group-functionalized materials, and furthermore the resulting nanocomposites can be endowed with the more integrated functionalities such as energy storage as well as the dispersion stability. S20

21 (a) (b) Figure S15. (a) ATR-FTIR absorbance spectra of rgo SO 3 cast from deposition solutions with different ph values. (b) UV-vis absorbance of (rgo SO 3 /OA-Fe 3 O 4 NP) n films as a function of the bilayer number for films assembled at different solution ph conditions of rgo SO 3. S21

22 (a) (b) Figure S16. Total film thickness of the (rgo SO 3 /OA Fe 3 O 4 NP) n multilayers as a function of the bilayer number (i.e., 40 nm for 5 bilayers, 68 nm for 10 bilayers, 102 nm for 15 bilayers, and 142 nm for 20 bilayers). (b) Frequency and mass change of (rgo SO 3 /OA-Fe 3 O 4 NP) n multilayers as a function of the layer number measured using a quartz crystal microbalance (QCM). In this case, the ΔF (or mass change, Δm) of the rgo-so 3 and OA-Fe 3 O 4 NPs were 6 ± 2 (Δm, ~90 ng cm 2 ) and 123 ± 14 Hz (Δm ~2170 ng cm 2 ), respectively. S22

23 (a) (b) Figure S17. (a) CVs of the (rgo-so 3 /OA-Fe 3 O 4 NP) n=5~20 multilayer electrodes in 0.1 M Na 2 SO 3 at a scan rate of 10 mv s -1. The areal current density unit (ma cm 2 ) of CVs shown in Figure 5a was transformed to volumetric current density unit (ma cm 3 ). (b) Volumetric capacitances of the (rgo SO 3 /OA Fe 3 O 4 NP) n=5~20 multilayer electrodes. S23

24 (a) (b) Figure S18. (a) Galvanostatic charge-discharge curves of (rgo-so - 3 /OA Fe 3 O 4 NP) 20 electrodes at current densities ranging from 1 to 6.5 A g 1. (b) Galvanostatic charge-discharge curves of (rgo SO 3 /OA Fe 3 O 4 NP) 20, the electrostatic (rgo SO 3 /rgo NH + 3 ) 20, and (rgo-so 3 /cationic Fe 3 O 4 NP) 20 electrodes at current density of 1 A g 1. S24

25 References and Notes [S1] Lin, X. Z.; Teng, X.; Yang, H. Langmuir 2003, 19, [S2] Sun, S.; Zeng, H. J. Am. Chem. Soc. 2002, 124, [S3] Sun, S.; Zeng, H.; Robinson, D. B.; Raoux, S.; Rice, P. M.; Wang, S. X.; Li, G. J. Am. Chem. Soc. 2004, 126, 273. [S4] Ko, Y.; Baek, H.; Kim, Y.; Yoon, M.; Cho, J. ACS Nano 2013, 7, 143. [S5] Pan, D.; Zhao, N.; Wang, Q.; Jiang, S.; Ji, X.; An, L. Adv. Mater. 2005, 17, [S6] Si, Y.; Samulski, E. T. Nano Lett. 2008, 8, [S7] Xiong, Z.; Gu, T.; Wang, X. Langmuir 2014, 30, 522. [S8] Lee, S. W.; Kim, B.-S.; Chen, S.; Shao-Horn, Yang,; Hammond, P. T. J. Am. Chem. Soc. 2009, 131, 671. [S9] Na, H. B.; Lee, J. H.; An, K.; Park, Y. I.; Park, M.; Lee, I. S.; Nam, D. H.; Kim, S. T.; Kim, S. H.; Kim, S. W.; Lim, K. H.; Kim, K. S.; Kim, S. O.; Hyeon, T. Angew. Chem. Int. Ed. 2007, 119, [S10] Park. J.; An, K.; Hwang, Y.; Park, J. E.; Noh, H. J.; Kim, J. Y.; Park, J. H.; Hwang, N. M.; Hyeon, T. Nat. Mater. 2004, 3, 891. [S11] Poddar, P.; Telem-Shafir, T.; Fried, T.; Markovich, G. Phys. Rev. B 2002, 66, [S12] Cheong, S.; Kim, Y.; Kwon, T.; Kim, B. J.; Cho, J. Nanoscale 2013, 5, [S13] Buttry, D. Advances in Electroanalytical Chemistry: Applications of the QCM to Electrochemistry; Marcel Dekker: New York, [S14] Zhao, G.; Jiang, L.; He, Y.; Li, J.; Dong, H.; Wang, X.; Hu, W. Adv. Mater. 2011, 23, [S15] Tung, V. C.; Allen, M. J.; Yang, Y.; Kaner, R. B. Nat. Nanotechnol. 2009, 4, 25. S25