Mei Zhang High-Performance Materials Institute, Florida State University, Tallahassee, FL, 32310, USA

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1 Supporting Information Alternative Nanostructures for Thermophones Ali E. Aliev 1, Nathanael K. Mayo, Monica Jung de Andrade, Raquel O. Robles, Shaoli Fang, and Ray H. Baughman A.G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, TX, 75083, USA Mei Zhang High-Performance Materials Institute, Florida State University, Tallahassee, FL, 32310, USA Yongsheng Chen Institute of Polymer Chemistry, College of Chemistry, Nankai University, Tianjin , China Jae Ah Lee, Seon Jeong Kim Center for Bio-Artificial Muscle and Department of Biomedical Engineering, Hanyang University, Seoul, , South Korea S1. Single layer MWNT sheet as a reference nanostructure for thermoacoustic heaters. (a) (b) Figure S1. a) The sound pressure spectra of a single MWNT sheet measured at a distance of 3 cm in open air at T 0 = 25 o C. The sound pressures are normalized to the applied ac power, P h ~ 0.3 W. The red and blue open circles show the p rms (f) response of a 1x1 cm 2 MWNT sheet measured by the low frequency (2 Hz-20 khz) precision microphone model 7046 (ACO Pacific, Inc.) and high frequency microphone B&K 4138-A-015 (6 Hz-140 khz), respectively. The brown open squares show the deviation of p rms (f) from linear dependence for the large (5 x 5 cm 2 ) single layer MWNT sheet shown in Figure S2b. This deviation is caused by destructive interference of signals coming from opposite edges of the large sample when the sound wavelength becomes comparable to the sample dimension. The green dashed line shows the theoretical line predicted by Equation 1. 1 Corresponding author. Tel.: ; fax: ; Ali.Aliev@utdallas.edu.

2 2 S2. Heat capacity of a freestanding MWNT forest. Figure S2. The temperature dependence of heat capacity for a 4 mm tall freestanding MWNT forest (2x3x4 mm 3 ) measured using the PPMS (Quantum Design Inc.) heat capacity option utilizing thermal relaxation technique. The 4 mm tall, vertically aligned MWNT forest was attached to the sample platform using low temperature H-grease (Quantum Design Inc.). S3. Heat capacity of ITO-coated PAN nanofiber sheet. Figure S3. The temperature dependence of the heat capacity of ITO-coated PAN nanofiber sheet, after twisting into a dense yarn and pressing into a round disk (D = 5 mm, h = 1 mm) for DSC Q2000 measurements. The inset shows the as-measured plot taken using the quasi-isothermal modulated method (T mod. = 1 K, t mod. period = 60 s, ΔT = 5 K).

3 3 S4. Evaluation of thermodynamic parameters used in Table Freestanding MWNT sheet. From literature data and new results in [2, 3]: C p (graphite) = 716 J/kg K, graphite = 2.267x10 3 kg/m 3 close packed MWNT=0.68 graphite = 1.55x10 3 kg/m 3 Density of aerogel sheet, sheet = 1 kg/m 3 = 50 W/m K = 45x10-6 m 2 /s C p = / close packed CNTs = 716 J/kg K C * h (HCPUA) = h C p =18x10-6 m x1.0 kg/m 3 x716 J/kg K = 13x10-3 J/m 2 K C volumetric (close packed MWNT) = C p = 1.0 kg/m 3 x716 J/kg K = 0.716x10 3 J/m 3 K C volumetric (air) = 0C p = kg m -3 x J kg -1 K -1 = 1.191x10 3 J/m 3 K From L. Xiao et al, [1]: From one wafer a times larger freestanding sheet can be withdrawn. Typical mass per unit area 1.5 g/cm 2 forest = M (4" forest mass) /V 30.6 kg/m 3 sheet = forest/ kg/m 3 C p (CVD grown CNT) 500 J/kg K c p (4" wafer) 500 J/kg K x 6x10-5 kg = 3x10-2 J/K S wafer = D 2 /4 = 3.14x0.01/ m 2 S sheet = S wafer x m 2 C * h (HCPUA) = c p /S sheet 7.65x10-3 J/m 2 K. C * h (HCPUA) in [1] x 10-3 J/m 2 K 2. Freestanding MWNT forest If the forest increases its surface area during dry-state spinning 300 times (i.e. 3 m long sheet from 1 cm 2 forest) and decreases its thickness 12.5 times (250 to 18 m), then the volume increases 300/12.5 = 24 times. Hence, the density of a forest is sheet x 24=1.5 x 24 =36 kg/m 3. Measured: V = 3.4 x 3.4 x cm 3 = cm 3 h = 243 m measured using SEM. Density: =M/V= mg/0.281 cm 3 = kg/m m thick forest: C h * (HCPUA) = C p h = x 716 x 0.243x10-3 = 5.5 J/m 2 K 80 m thick forest: C h * (HCPUA) = C p h = x 716 x 0.08 x10-3 = 1.8 J/m 2 K (1x1 cm 2 ) 3. MWNT Aerogel Sponge The density of the sample used in measurements was ~ 30 kg/m 3 Using the above measured heat capacity of MWNT forest and the value accepted for graphite, C p = 716 J/kg K, C * h (HCPUA) = C p h = 30 x 716 x 10-4 = 2.15 J/m 2 K (2x2.5 cm 2 )

4 4 For comparison, a SWNT sponge having a density of about 1290 m 2 /g [4]. = kg/m 3 has a specific surface area of 4. Graphene Sponge For density and heat capacity measurement we laser cut a round-shape plate of the graphene sponge (GS) perpendicular to the cylinder axis: D = 17.5 mm, h = 2.3 mm, S = 240 mm 2, V = cm 3, M = mg = 2.75 kg/m 3. The heat capacity of GS measured using isothermal MDSC at 295 K to be C p = 0.69 J/g K. For TA measurements, we prepared three laser cuts: h 1 =1.5 mm, h 2 =1.0 mm, h 3 =0.8mm C * h (HCPUA) 2 = C p h = 2.75 x 690 x 0.8x10-3 = 1.5 J/m 2 K The density of sample shown in above picture measured at UTD is 2.75 kg/m 3. The thermal conductivity measured at UTD using the 3-omega method: = C p = W/m K. The thermal diffusivity: II = 2.25 mm 2 /s, = 2.31 mm 2 /s For comparison [6]: = kg/m 3, most results in Ref. [6] obtained for 5.51 kg/m Sheets of Gold-Coated Poly(acrylonitrile) Nanofibers PAN - C 3 H 3 N (Molar Weight =53) PAN = g/cm 3 Au = 19.3 g/cm 3 C p (Au) = 129 J/kg K [wikipedia.com] C p (PAN) = J/mol K=1300 J/kg K [7], C p (PAN) = 1260 J/kg K [8]. Measured at UTD: Areal density of PAN sheet, areal = 0.03 mg/cm 2, Initial optical transparency T=85% Areal density of Sb 2 Te 3 / PAN, areal = 0.15 mg/cm 2 (averaged among of 10 samples). Areal density of Au/ PAN, areal = 0.31mg/cm 2 (estimated using Au/ Sb2Te3 =19.3/7.7 ratio). Thickness of Au/PAN sheet: (the same as for PAN/Sb 2 Te 3 and ITO/PAN) : h = 5 ± 0.2 m Areal density of electrospun PAN nanofiber sheet Width (cm) Length (cm) S Vx10 3 cm 2 cm 3 Weight (mg) areal (mg/cm 2 ) (mg/cm 3 ) #1 3.98/ #2 3.88/ #3 4.18/

5 5 The average areal density of the measured PAN sheets is 0.03 mg/cm 2, and their average density is 60 mg/cm 3 The density of PAN sheets calculated from the areal density for h = 5 m: PAN = areal /h = 60 mg/cm 3. When depositing an Au layer on the PAN fibers, the porosity of the PAN sheet changes negligibly, but the density increases. Let s calculate the C h * from known values of C p for gold and PAN: If the averaged diameter of electrospun fibers is d core = 0.5 m (see SEM images in main text) and after coating D = 0.6 m, then S o = D 2 /4 = 0.283x10-8 cm 2, S core = 0.196x10-8 cm 2, S Au = cm 2. The thickness normalized mass: PAN S core + Au S Au = 1.184x x0.087 = 0.232x x10-8 =1.912x10-8, i.e. the Au/PAN sheet becomes heavier then the PAN sheet 8.24 times. Au/PAN = PAN x 8.24 = 0.06 g/cm 3 x 8.24 = g/cm 3 = 494 kg/m 3. The averaged heat capacity of the Au/PAN sheet: C p = A 1 xc p PAN +A 2 xc p Au =0.121x x129 = 266 J/kg K, where the weight coefficients for the constituent PAN and gold are, A 1 +A 2 = = 1. C h * (HCPUA) = C p h = 494 kg/m 3 x 266 J/kg K x m = 0.66 J/m 2 K. C h * (HCPUA) estimated directly from the measured areal surface density: (M/h S) C p h = areal C p = kg/m 2 x 266 J/kg K= 0.84 J/m 2 K. 6. ITO/PAN sheet PAN - C 3 H 3 N (Molar weight 53) Density of PAN (bulk) = g/cm 3 Density of ITO = g/cm 3 C p (PAN) = J/mol K=1300 J/kg K [7]. C p (ITO) =362 J/kg K [Wikipedia] Measured at UTD: Areal density of PAN sheet, areal = 0.03 mg/cm 2, Initial optical transparency, T=95%. Areal density of Sb 2 Te 3 / PAN, areal = 0.15 mg/cm 2 (averaged among of 10 samples). Areal density of ITO/PAN = Sb 2 Te 3 / PAN x (7.124/7.7)=0.139 mg/cm 2. The transparency does not change with ITO coating. The thickness of ITO/PAN sheet is the same as for PAN/Sb 2 Te 3 sheet, h = 5 ± 0.2 m If the averaged diameter of electrospun fibers is d core =0.5 m and with coating D = 0.6 m (SEM data), Cross-section area: S o = D 2 /4 = 0.283x10-8 cm 2, S core = 0.196x10-8 cm 2, S ITO = cm 2. For the double sided ITO deposited PAN sheets (assuming the length of fiber and coatings are the same) the averaged density normalized to the thickness is: PAN S core + ITO S ITO = 1.184x x0.087 = 0.232x x10-8 = x10-8, i.e. the ITO/PAN sheet becomes heavier then the PAN sheet 3.67 times. For single side ITO deposited PAN sheets:

6 6 PAN S core + Au S ITO = 1.184x x0.087/2 = 0.232x x10-8 =0.542 x10-8, i.e. the ITO/PAN sheet becomes heavier then the PAN sheet 2.33 times. Then, ITO/PAN = PAN x 3.67 = 0.06 g/cm 3 x 3.67= 0.22 g/cm 3 = 220 kg/m 3. half-ito/pan = PAN x 2.33 = 0.06 g/cm 3 x 3.67= 0.14 g/cm 3 = 140 kg/m 3. The averaged heat capacity of ITO/PAN sheet: C p (both-side) = A 1 xc p PAN +A 2 xc p ITO =0.272x x362 = 606 J/kg K, where weight coefficient for constituent PAN and ITO are, A 1 +A 2 =( )/0.852 = = 1. C p (half-ito) = A 1 xc p PAN +A 2 xc p ITO =0.428x x362 = 746 J/kg K, where weight coefficient for constituent PAN and ITO are, A 1 +A 2 = ( )/0.542 = = 1. HCPUA(double side coated) = C p h =220 kg/m 3 x 606 J/kg K x m = 0.67 J/m 2 K. HCPUA(single side coated) = C p h =140 kg/m 3 x 746 J/kg K x m = 0.52 J/m 2 K. References: 1. L. Xiao, Z. Chen, C. Feng, L. Liu, Z.-Q. Bai, Y. Wang, L. Qian, Y. Zhang, Q. Li, K. Jiang, S. Fan. Flexible, Stretchable, Transparent Carbon Nanotube Thin Film Loudspeakers. Nano Lett. 2008, 8, A. E. Aliev, M. D. Lima, E. M. Silverman, R. H. Baughman, Thermal conductivity of multi-walled carbon nanotube sheets: radiation losses and quenching of phonon modes, Nanotechnology, 2010, 21, A. E. Aliev, C. Guthy, M. Zhang, Sh. Fang, A. A. Zakhidov, J. E. Fischer, R. H. Baughman. Thermal transport in MWCNT sheets and yarns. Carbon , K. H. Kim, Y. Oh, and M. F. Islam. Mechanical and Thermal Management Characteristics of Ultrahigh Surface Area Single-Walled Carbon Nanotube Aerogels. Adv. Funct. Mater. 2013, 23, Y. Wu, N. Yi, L. Huang, T. Zhang, Sh. Fang, H. Chang, N. Li, J. Oh, J. Lee, M. Kozlov, A. C. Chipara, H. Terrones, P. Xiao, G. Long, Y. Huang, F. Zhang, L. Zhang, X. Lepro, C. Haines, M. D. Lima, N. P. Lopez, L. P. Rajukumar, A. L. Elias, S. Feng, S. J. Kim, N. T. Narayanan, P. M. Ajayan, M. Terrones, A. Aliev, P. Chu, Zh. Zhang, R. H. Baughman, and Y. Chen, Three-dimensionally bonded spongy graphene material with super compressive elasticity and near-zero Poisson s ratio, Nat. Commun. 2015, DOI: /ncomms 7141, online. 6. L. Qiu, J. Z. Liu, S. L. Wu, Y. Chang, & D. Li. Biomimetic superelastic graphene-based cellular monoliths. Nat. Commun. 2012, 3, U. Gaur, S.-T. Lau, B. B. Wunderlich, B Wunderlich, Heat Capacity and Other Thermodynamic Properties of Linear Macromolecules, VI Acrylic Polymers, J. Phys. Chem. Ref. Data, 1982, 11, Polymers: A Property Database, 2nd Edition, ed. by B. Ellis, R. Smith, CRC Press, 2008.