Supporting Information

Transcription

1 Supporting Information Ultralight Conductive Silver Nanowire Aerogels Fang Qian 1,*, Pui Ching Lan 1, Megan C. Freyman 1, Wen Chen 2, Tianyi Kou 3, Tammy Y. Olson 1, Cheng Zhu 2, Marcus A. Worsley 1, Eric B. Duoss 2, Christopher M. Spadaccini 2, Ted Baumann 1, T. Yong-Jin Han 1,* 1 Physical and Life Science Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, U.S.A 2 Engineering Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, U.S.A 3 Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, U.S.A * Corresponding authors: Fang Qian (qian3@llnl.gov); T. Yong-Jin Han (han5@llnl.gov) 1

2 Experimental methods and instrumentation. All chemicals and solvents were purchased from Sigma-Aldrich (St. Louis, MO) and used as received. The scanning electron microscope images were collected in a JEOL-JSM-7401F field emission SEM. The transmission electron microscope images and diffraction pattern were taken by a FEI Titan S TEM. XRD was done with a Bruker AXS D8 Advance diffractometer. Diffraction patterns were recorded from 10 to 75 2θ with a step size of at 1.5 second per step. The TGA thermal analysis was performed on a NETZSCH STA 449 F3 Jupiter. FT-IR studies were performed using an ALPHA FTIR Spectrometer (Bruker Inc). The weights of the aerogel samples were measured by a Mettler Toledo ultra-microbalance (Model # XP2U). The frozen samples were lyophilized in a Labconco benchtop freeze dry system (FreeZone -105 C 4.5-L Cascade system). Synthesis of silver nanowires (150-ml scale). For a typical synthesis, 100 ml of ethylene glycol (EG) containing NaCl (0.05 mm), PVP MW = 55K (0.189 M), AgNO 3 ( mm) and CuCl 2 (0.017 mm) was added to a round-bottom flask and pre-heated at 185 C in an oil bath for 1 hr. Subsequently, 30 ml of freshly prepared AgNO 3 in EG (0.12 M) was added drop-wise to the flask; vigorous stirring until all 30ml was added. After injection, the flask was heated for 20 more minutes before being removed from the oil bath and cooled down in air to room temperature. Purification of silver nanowires. We used a modified procedure from reference #22. In short, the AgNW are purified by sedimentation and selective precipitation of NWs by addition of acetone. First, the as-made AgNW solution in EG was diluted with water and placed overnight for sedimentation. Next, the supernatant was carefully decanted, and water was added back to its 2

3 original volume, which is left to sediment for another night. After decanting for the second time, ~50 ml of water was added to the pallet to make a stock AgNW solution. For purification, the AgNW stock solution was mixed with acetone, vortexed and centrifuged. Remove the supernatant which contains most Ag NPs. The pellet was collected, resuspended in aqueous solution containing PVP (5 w/v%), and vortexed until the pellet was dissolved. Add acetone again for selective precipitation of NWs. Repeat this process for several times until NPs are removed to a satisfying degree. Lastly, precipitate the AgNW again with acetone, and resuspend the NW pallet in water. The concentration of the NW aqueous suspension is calibrated by measuring the weight of the dry content in a 1 ml solution using an ultramicrobalance. TGA analysis. The sample was heated up to 650 C in a silicon carbide furnace at a heating rate of 5K/min, in an open Pt crucible. The heating was conducted under Ar gas flow set at 100 ml/min. A sample weight of at 8 mg was used for PVP while the sample weight of the aerogel was 3-5 mg. Electrical measurement. The electrical measurement was carried out using a multi-height probe with RM3000 test unit. Aerogels of different densities were fabricated into disc geometries. The disc has a diameter of 10 mm and a thickness of 0.25 mm. For each sample, its sheet resistance (Rs) were measured from multiple sites to obtain an averaged value. The resistivity (ρ) is calculated by ρ= h. The conductivity is calculated by σ=1/ρ. 3

4 Mechanical test. Aerogels of different densities were fabricated into cylinders, with a diameter of 10 mm and a height of 5 mm (aspect ratio=0.5). The samples were measured using a universal testing machine (Instron 5943) equipped with a 5 N load cell under a quasi-static strain rate of s -1. 4

5 Fig. S1 Purification of Ag NWs. (a-c) Optical microscope images of unpurified Ag NWs in an aqueous solution, enriched Ag NPs in the acetone/water supernatant, and purified Ag NWs. (d-e) SEM images of unpurified and purified Ag NWs. Scale bars are 2 µm. (f) XRD data recorded from purified Ag NWs. Fig. S2 AgNW aerogels prepared by freeze-casting method. Note pores are anisotropic. 5

6 Fig. S3 AgNW aerogels prepared by isotropic-freezing method. Note pores are spherical and isotropic. Fig. S4 Comparison of AgNW aerogels before and after thermal sintering. (a) Digital photograph showing the results after a sintered (red) and an un-sintered (blue) aerogel were placed in a dish that contained water. (b, c) Low-resolution TEM images of un-sintered aerogels. (d,e) Lowresolution TEM images of sintered aerogels. Welded junctions are present. Inset: electron diffraction pattern recorded from the junction area in the dashed circle. 6

7 Fig. S5 (a) FT-IR spectra of PVP (dotted line), as-made (dashed line) and sintered (solid line) AgNW aerogels. (b) TGA analysis of PVP (dotted line) and sintered (solid line) AgNW aerogel. Fig. S6 (a) Relative conductivity plot as a function of relative density of sintered (black solid line) and un-sintered (grey dash line) AgNW aerogels. (b) Raw data of 4-probe electrical measurement recorded from representative sintered aerogels. 7