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1 Cocoon-in-Web-like Superhydrophobic Aerogels from Hydrophilic Polyurea and Use in Environmental Remediation Nicholas Leventis *, Chakkaravarthy Chidambareswarapattar, Abhishek Bang and Chariklia Sotiriou-Leventis * Department of Chemistry, Missouri University of Science and Technology, Rolla, MO 65409, U.S.A. leventis@mst.edu, cslevent@mst.edu Supporting Information Page No. Index... S.1 Appendix S.1 Appendix S.2 Rheometry S.2-S.3 Small angle X-ray scattering (SAXS)... S.4-S.5 Appendix S.3 X-ray Diffraction (XRD)... S.6 Appendix S.4 Thermal conductivity S.7-S.9 Appendix S.5 Oil absorption data S.10 Appendix S.6 Movies S.1-S.3 (in separate files) S.11 S-1

2 Appendix S.1 Rheometry A. B. Figure S.1. Typical rheometry data during gelation of PUA sols. (A) Evolution of the storage modulus (G dark circles), loss modulus (G - open circles) and tanδ (triangles) vs. time of a PUA-ACN-109 sol ([N3300A]=0.109 M). Oscillation frequency ω=1 rad s -1. (B) Log of statistical variable versus time. Formal gelation point at the minimum. S-2

3 Table S.1. Rheometry data from the gelation of selected PUA sols as indicated sol formulation aging time before loading to rheometer (s) gelation point, t gel a (s[s]) tanδ at t gel n b D f c PUA-acetone [10800] PUA-DMF [10800] PUA-ACN [1320] PUA-ACN [600] a Identified at the minimum of the statistical function, log(s/tan δ), SI-R.1 as shown in Figure S.1 (s: standard deviation of tan δ between the four frequencies employed (see Experimental Section), at each time point.) In brackets, phenomenological gelation times (by inverting the molds). At the gel point, tan δ is related to the gel relaxation exponent n via Eq. S.1. SI-R.2 tan δ =tan (nπ/2) (S.1) considering the excluded volume of the (primary) particles forming the clusters, n is related via Eq. S.2 to the mass fractal dimension, D f, of the clusters forming the gel. SI- R.3 (Note, for three-dimensional non-fractal clusters, D f =D=3. SI-R.3 ) n = D(D + 2 2D f ) 2(D + 2 D f ) (S.2) b c From Eq. S.1. From Eq. S.2. The D f values of the selected PUA formulations (Table S.1) are in the range, suggesting that the gel network is formed by mass-fractal particles. SI-R.4 SI-R.1 Kim, S.-Y.; Choi, D.-G.; Yang, S.-M. Korean J. Chem. Eng. 2002, 19, SI-R.2 Raghavan, S. R.; Chen, L. A.; McDowell, C.; Khan, S. A.; Hwang, R.; White, S. Polymer 1996, 37, SI-R.3 Muthukumar, M. Macromolecules 1989, 22, SI-R.4 Kolb, M.; Botet, R.; Jullien, R. Phys. Rev. Lett. 1983, 51, S-3

4 Appendix S.2 Small angle X-ray scattering (SAXS) A. IV III II I B. IV III II I C. IV III II I Q (Å -1 ) Figure S.2. Representative small angle X-ray scattering (SAXS) data for PUA aerogels synthesized in different solvents, (A) PUA-acetone-109. (B) PUA-ACN-109. (C) PUA- DMF-109 (i.e., in all cases the monomer concentration in the sol [N3300A]=0.109 M). Data were fitted to the Beaucage Unified Model. SI-R.5,SI-R.6 Results are summarized in Table S.2. (Region I: high-q power low; Region II: first Guinier knee; Region III: second (low-q) power law; Region IV: second Guinier knee. S-4

5 Table S.2. SAXS characterization data of PUA aerogels Primary Particles Secondary Particles sample bulk density high-q R G(1) R 1 low-q R G(2) R 2 in acetonitrile ρ b (g cm -3 ) slope a (nm) b (nm) c slope d (nm) e (nm) f PUA-ACN ± ± ± ± ± ± ± 3.8 PUA-ACN ± ± ± ± ± ± ± 2.1 PUA-ACN ± ± ± ± ± ± ± 2.9 PUA-ACN ± ± ± ± ± ± ± 4.9 in DMF PUA-DMF ± ± ± ± ± ± ± 0.3 PUA-DMF ± ± ± ± g g g in acetone PUA-acetone ± ± ± ± ± ± ± 0.8 PUA-acetone ± ± ± ± ± ± ± 0.8 PUA-acetone ± ± ± ± 0.1 g g g PUA-acetone ± ± ± ± 1.3 g g g Referring to Figure S.2: a From power-law Region I. Slopes<-4.0, signifying primary particles with densitygradient boundaries. b First radius of gyration R G (1), from Guinier Region II. c Primary particle radius = R G (1)/0.77. d From power-law Region III. Slopes>-3.0 signify mass-fractal assemblies with mass fractal dimensions, D m = slope. Slopes<-3.0 signify close-packed surface-fractal assemblies, with surface fractal dimensions, D s =6- slope. The latter is the case of all PUA-ACN-xxx materials. e Second radius of gyration R G (2), from Guinier Region IV. f Secondary particle radius = R G (2)/0.77. g Not within the accessible low-q range. SI-R.5 (a) Beaucage, G. J. Appl. Crystallog. 1995, 28, (b) Beaucage, G. J. Appl. Crystallog. 1996, 29, SI-R.6 Ilavsky, J.; Jemian, P. R. J. Appl. Crystallog. 2009, 42, S-5

6 Appendix S.3 X-ray diffraction (XRD) data PUA-acetone-109 (50%) PUA-ACN-109 (67%) PUA-DMF-109 (40%) Figure S.3. XRD of low-density samples as shown. Degrees of crystallinity (given in parentheses) were calculated from the areas above the broad background of each sample. (For other sample information refer to Table 1 in the main article.) S-6

7 Appendix S.4 Thermal conductivity Total thermal conductivities, λ, were determined using a laser flash method for all PUA- ACN-xxx aerogels from their thermal diffusivities (R), heat capacities (c P ) and bulk densities (ρ b ), via Eq. S.3, as described previously. SI-R.7 Table S.3 summarizes the data, λ = ρ b c P R (S.3) and Figure S.4A shows the variation of λ with ρ b. Thermal conductivities fall in the range W m -1 K -1, that is similar to that of PUA-acetone-xxx aerogels. SI-R.8 Table S.3. Thermal conductivity data of the PUA-ACN-xxx aerogels at 23 o C Sample Bulk density ρ b (g cm -3 ) Thermal diffusivity R (mm 2 s -1 ) Total thermal conductivity λ (W m -1 K -1 ) Gaseous thermal conductivity λ g (W m -1 K -1 ) a Solid thermal conductivity λ s (W m -1 K -1 ) b PUA-ACN ± ± ± PUA-ACN ± ± ± PUA-ACN ± ± ± PUA-ACN ± ± ± PUA-ACN ± ± ± a b From Knudsen s equation (Eq. S.5). From λ s =λ-λ g (Eq. S.4). Assuming no coupling of the heat transfer modes, λ can be considered as the sum of three contributors (Eq. S.4), whereas λ g is the non-convective thermal conductivity λ = λ g + λ s + λ irr (S.4) through the pore-filling gas, λ s is the thermal conductivity through the solid framework and λ irr is the radiative heat transfer. The latter was minimized experimentally, and the remaining portion was removed from the data digitally. Quantitatively, the relative contributions of λ g and λ s to the total λ can be assessed by calculating λ g using Knudsen s equation (Eq. S.5). SI-R.9 where λ g,o is the intrinsic conductivity of the poreλ λ g = g,o Π (S.5) 1+ 2β(l g / Φ) filling gas (for air at 300 K at 1 bar, λ g,o = W m -1 K -1 ), SI-R.10 Π is the porosity in decimal notation (data from Table 1), β is a parameter that accounts for the energy S-7

8 transfer between the pore-filling gas and the aerogel walls (for air β=2), l g is the mean free path of the gas molecules (for air at 1 bar pressure, l g 70 nm) and Φ is the pore diameter, calculated via the 4 V Total /σ method, (V Total =(1/ρ b )-(1/ρ s )) (see Table 1 of the main article). In this context, it is noted also that λ g,o is the upper limit of λ g for Π=1 and Φ ; as ρ b increases, both Π and Φ decrease, hence λ g decreases from λ g,o monotonically. Therefore, at some point the solid framework becomes the main conductor of heat. Both λ g and λ s of PUA-ACN-xxx aerogels are included in Table S.3. The variation of λ s with ρ b has been modeled with an exponential expression, Eq. S.6. SI-R.11, SI-R.12 λ s = C (ρ b ) a (S.6) Exponent α depends on how matter fills space. For foams α=1; for silica aerogels α~1.5. The pre-exponential factor C depends on the particle chemical composition and the interparticle coupling (neck area and extent of interparticle bonding). Exponent α and coefficient C for the PUA-ACN-xxx aerogels were calculated from Log-Log plots; results are shown in Figure S.4B and are compared with results obtained with PUAacetone-xxx using the hot-wire method. SI-R.8 SI-R.7 Parker, W. J.; Jenkins, R. J.; Butler, C. P.; Abbott, G. L. J. Appl. Phys. 1961, 32, SI-R.8 Weigold, L.; Mohite, D. P.; Mahadik-Khanolkar, S.; Leventis, N.; Reichenauer, G. J. Non-Cryst. Solids 2013, 368, SI-R.9 (a) Lu, X.; Arduini-Schuster, M. C.; Kuhn, J.; Nilsson, O.; Fricke, J.; Pekala, R. W. Science 1992, 255, (b) Reichenauer, G.; Heinemann, U.; Ebert, H.- P. Colloids Surf. A 2007, 300, SI-R.10 Stephan, K.; Laesecke, A. J. Phys. Chem. Ref. Data 1985, 14, SI-R.11 Lu, X.; Caps, R.; Fricke, J.; Alviso, C. T.; Pekala, R. W. J. Non-Cryst. Solids 1995, 188, SI-R.12 Lu, X.; Nilsson, O.; Fricke, J.; Pekala, R. W. J. Appl. Phys.1993, 73, S-8

9 A. B. PUA-ACN-xxx Slope: 0.99 Intercept: 0.13 R 2 = 0.97 PUA-acetone-xxx Slope: 1.00 Intercept: 0.10 R 2 = 1.00 log (ρ b, g cm -3 ) Figure S.4. (A) Total thermal conductivity, λ, of PUA-ACN-xxx aerogels as a function of the bulk density, ρ b, using a laser flash method (see Experimental section in the main article). (B) Log-Log plot of the solid thermal conductivity, λ s, versus bulk density of PUA-ACN-xxx and PUA-acetone-xxx aerogels, as indicated.data for the latter using the hot-wire method, from Ref. SI-R.8. (Intercepts in W m -1 K -1.) S-9

10 Appendix S.5 Oil absorption data Table S.4. Oil adsorption data for all aerogel samples of this study a Sample Bulk density ρ b (g cm -3 ) Porosity Π (% v/v) Aerogel sample weight (g) Free volume in sample (cm -3 ) Theoretical mass of oil needed to fill the free volume (g) Mass of sample after 12 h in oil-onwater (g) Mass of sample after 20 min straining on paper (g) Mass of oil uptaken (g) (Mass of oil) : (Mass of aerogel) w/w fraction of theoretical oil uptake PUA-ACN PUA-ACN PUA-ACN PUA-ACN PUA-DMF PUA-DMF PUA-acetone PUA-acetone PUA-acetone PUA-acetone a For experimental details see Experimental section in the main article. Bulk densities and porosities from Table 1 of the main article. Density of oil used ρ oil = g cm -3. S-10

11 Appendix S.6 Movies S.1-S.3 (in separate files) Movie S.1. Bending a flexible PUA-ACN-109 monolith (ρ b =0.073 g cm -3 ) Movie S.2 Bending a rigid PUA-acetone-109 monolith (ρ b =0.075 g cm -3 ) Movie S.3 Oil absorption from water with a PUA-ACN-109 monolith (ρ b =0.073 g cm -3 ; Π=94% v/v see Table 1 of the main article) (weight of aerogel monolith: g; weight of oil: 1.00 g) S-11