Supporting Information

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1 Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, Supporting Information for Adv. Mater., DOI: /adma Mechanically Flexible and Multifunctional Polymer-Based Graphene Foams for Elastic Conductors and Oil-Water Separators Chao Wu, Xingyi Huang,* Xinfeng Wu, Rong Qian, and Pingkai Jiang *

2 Supporting Information Mechanically Flexible and Multifunctional Polymer-Based Graphene foams for Elastic Conductors and Oil-Water Separators Chao Wu, Xingyi Huang*, Xinfeng Wu, Rong Qian, and Pingkai Jiang* C. Wu, Dr. X. Huang, X. Wu, R. Qian, and Prof. P. Jiang. Department of Polymer Science and Engineering Shanghai Key Lab of Electrical Insulation and Thermal Aging Shanghai Jiao Tong University, Shanghai , P. R. China Dr. X. Huang, Prof. P. Jiang. Shanghai Engineering Center for Material Safety of Nuclear Power Equipment Shanghai Jiao Tong University, Shanghai , P. R. China Keywords: polymer-based graphene foam; elastic conductor; oil-water seperation; selfassembly Experimental: Materials: Materials: Natural graphite powder (40 um with purity>99.85%) and hydrazine hydrate (85%) were purchased from Sinapharm Chemical Reagent co., Ltd, China. Preparation of Graphene oxide (GO): In a typical experiment, Graphite powder (3 g) was put into an H 2 SO 4 solution (12 ml) containing K 2 S 2 O 8 (2.5 g) and P 2 O 5 (2.5 g). The mixture was kept at 80 C for 4.5 h, cooled to room temperature, and then diluted with 0.5 L of de-ionized (DI) water. Then, the resulting mixture was filtered and washed with de-ionized (DI) water using a 0.2 micron Nylon Millipore filter. After vacuum filtration, the obtained product was vacuum-dried for 8 h at 100 C. This pre-oxidized graphite was then subjected to oxidation by Hummers method described as follows. Pretreated graphite powder was put into cold (0 C) concentrated H 2 SO 4 (120 ml).then, KMnO 4 (15 g) was added gradually under stirring and the temperature of the mixture was kept to be below 20 C by cooling. Subsequently, the mixture was stirred at 35 C for 2 h, and then diluted with DI water (250 ml). Because the addition of water in 1

3 concentrated sulfuric acid medium released a large amount of heat, the process of adding DI water was carried out in an ice bath to keep the temperature below 30 C. After adding 250 ml of DI water, the mixture was stirred for 1 h, and then added to additional 0.7 L of DI water. Subsequently, 30 ml of 30% H 2 O 2 was added to the mixture, and the color of mixture changed into brilliant yellow along with bubbling. The mixture was vacuum-filtered and washed with 1:10 HCl aqueous solution (1 L) to remove metal ions followed by 1 L of DI water to remove the acid. Finally, the resulting sample was purified by dialysis for one week to obtain GO solution. Fabrication of polymer-based graphene foams (PGFs) via a self-assembly method: In a typical process, 30 ml graphene oxide solution (1mg/ml) was added by 75 l hydrazine and stirred for 3 min at room temperature. Then, the mixture was poured into a 50 ml Teflon vessel, and a commercial polyurethane foam (30 ml) was immersed into the mixture by repeatedly squeezing the foam for 5 times. After squeezing, the vessel was placed in vacuum oven for 2 minutes under the pressure of Pa to remove the bubbles in the foam. Subsequently, the vessel was closed and placed in an oven and heated to 90 o C. After reaction for 12 h, a monolithic gel-like product was taken out from the vessel and directly dried to obtain the polymer based-graphene foams. The density of the resulting foams is about 24.6 mg/ml with 2 wt% graphene. We have fabricated the polymer-based graphene foams with graphene content ranging from 1% to 6% by adjusting the concentration of graphene oxide. The foams with lower or higher graphene content can be available by this protocol. Fabrication of graphene foams via a chemical reduction and cryodesiccation process In a typical process, 30 ml graphene oxide solution (2 mg/ml) was transferred to a sealed reactor and heated at 180 o C for 12 h. The reactor was cooled down, and then the as-prepared graphene gel was taken out from the reactor and freeze-dired to obtain graphene foams. 2

4 Characterization: The morphology and microstructure of the samples were investigated by FE-SEM (nanosem 230, NOVA, USA), TEM (JEM-2010, JEOL, Japan), XRD (D/max-2200/PC, Rigaku, Japan), and Raman (LabRam HR800, Jobin Yvon, France). Thermogravimetric analysis (TGA-209F3, NETZSCH, Germany) was carried out under a 20 ml/min N 2 purge at a heating rate of 10 C/min from room temperature to 800 o C. The real-time electrical resistance and conductivity variations of the samples were measured by a two-point device under mechanical deformation. In the measurement, two copper sheets severed as electrodes to connect to polymer-based graphene foam, which enables a strong contact at the junctions. Every electromechanical experiment was repeated by 5 times and the value of electrical resistance is the average value. The electrical conductivity of the samples at the original state was also measured by a four-probe instrument (PZ-158A-SB118, Qianfeng, China). Mechanical property tests were conducted using an SANS 4304 Electromechanical Tester with a crosshead speed of 10 mm/min at room temperature. Water contact-angles were measured on a DSA 30 contact-angle system (Kruss, Germany) at room temperature. 3

5 Figure S1. Photograph of large-sized, free-standing polymer-based graphene foams (PGFs) ( mm 3 ). 4

6 Figure S2. Photographs displaying the burning processes of pristine polyurethane foam and polymer-based graphene foam (PGF) in air, showing that the polyurethane foam disappears and polymer-based graphene foam remains an entire framework after burning. 5

7 Figure S3. SEM images of polymer-based graphene foams (PGFs) with different loading of graphene: (a) 1 wt%; (b) 2 wt%; (c) 4 wt%; (d) 6 wt%. 6

8 Figure S4. SAED patterns of graphene sheets striped from polymer-based graphene foams (PGFs), indicating that the graphene sheets are composed of mono- or multi-layer graphene based building blocks. (a) A set of hexagonal diffraction spots and (b-d) Multi-sets of hexagonal spots patterns. 7

9 Figure S5. (a) XRD patterns of Graphite, GO and graphene sheets; (b) Independent XRD pattern of graphene sheets, showing a peak at 2θ=24.5º. Figure S6. TGA curves of GO and graphene sheets, showing a 50 wt% and 15 wt% mass loss of organic groups from GO and graphene sheets, respectively. 8

10 Figure S7. Raman spectra of GO and graphene sheets, showing that a clear shift of G band from GO to GS. Figure S8. Optical images of polymer-based graphene foams (PGFs) under the bend and twist states, showing their excellent mechanically flexibility. 9

11 Figure S9. Electrical conductivity of polymer-based graphene foams (PGFs) as a function of filler weight fraction. 10

12 Figure S10. Photographs of a row of LED lamps showing that their brightness could be adjusted by the pressure on the polymer-based graphene foams (PGFs). 11

13 Figure S11. Photographs showing the water contact-angle of (a) the pristine polyurethane foam (the water contact-angle is about 85.6º); (b) polymer-based graphene foam (PGF) with 6 wt% graphene at pristine state (the water contact-angle is about 133.4º); (c) polymer-based graphene foam (PGF) with 6 wt% graphene after a compression of 50% towards center along the horizontal direction (the water contact-angle is about 141.1º). 12