Direct Observation of Metal Nanoparticles as Heterogeneous Nuclei for the Condensation of Supersaturated Organic Vapors Nucleation of Size-Selected Aluminum Nanoparticles in Acetonitrile and n-Hexane Vapors Victor Abdelsayed and M Samy El-Shall* Department of Chemistry, Virginia Commonwealth University Richmond, Virginia 23284-2006 Supplementary Materials 1 Description of the Diffusion Cloud Chamber (DCC) The DCC is used to produce a supersaturated host vapor under well-defined conditions of temperature, pressure and supersaturation A detailed description of the DCC and principles of its operation are available in the literature, 1-3 and only a brief description is given here (see Figure S1) The chamber consists of two aluminum circular plates separated by a glass ring The chamber is designed so that to a high degree of approximation, one dimensional diffusion takes place through a carrier gas from a lower heated pool of liquid to an upper metal plate at which the vapor molecules are condensed The chamber profiles showing supersaturation ratio, pressure, temperature, and density as a function of reduced height (obtained by solving the mass and heat transfer equations)1-3 are shown in Figure S1 (b) As vapor pressure is approximately an exponential function of temperature while temperature and partial pressure profiles in the chamber are almost linear, the vapor is supersaturated throughout the chamber The supersaturation can be made as large as desired by increasing the temperature gradient The critical state for homogeneous nucleation is defined as the point at which the temperature difference across the chamber is sufficient to yield a regular rain of drops (~1 drop/cm 3/sec) The onset of nucleation is determined by observing the forward scattering of light from drops falling through a horizontal He-Ne laser beam positioned at an elevation lower than 0.50 (reduced height) of the cloud chamber These drops originate near the elevation at which the maximum (peak) supersaturation occurs (~0.75 reduced height) The heights of the Al target, the ArF laser beam, the He-Ne laser beam, and the nucleation zone are 2.5, 2.3, 3.0, and 3.6 – 3.8 cm, respectively from the bottom plate of the DCC Condensed film 1.0 z/H Nucleation zone 0.5 He-Ne laser 0.0 50 Liquid pool PM T 270 280 290 Temperature (K) 100 Vapor Partial Pressure (torr) 1.0 1.5 2.0 Supersaturation Figure S1 (a) Schematic of the thermal Diffusion Cloud Chamber (DCC) Reduced Height 1.0 Peq (torr) 0.8 P (torr) 0.6 0.4 Density (gm cm-3) T (K) 0.2 0.0 300 350 Temperature 400 0.08 S = P/Peq 0.12 Density Pressure 12 10 -3 -1 J (cm s ) 20 Supersaturation 10 Rate (CNT) Normalized Intensity Figure S1 (b) Total vapor density, temperature, equilibrium vapor pressure, partial pressure and supersaturation profiles calculated for the observed nucleation of 1-3 drops/cm3/s for dodecane.3 (c) Al-CH3CN Figure S2 TEM for Al nanoparticles prepared in two differentSsupersaturated vapors of = 4.98 max n-hexane (a) S= 2.7 and (b) S= 3.9 (b) Al-CH3CN Al -Helium(193 nm) 220 200 (a) 111 Smax= 2.73 30 40 50 2θ 60 70 Figure S3 XRD patterns of Al nanoparticles prepared by laser vaporization (ArF laser, 193 nm) of an Al target in: (a) pure He gas, (b) supersaturated acetonitrile vapor with S = 2.73, and (c) supersaturated acetonitrile vapor with S = 4.98 Figure S4 XRD patterns of Al nanoparticles prepared by laser vaporization (ArF laser, 193 nm) of an Al target in: (a) pure He gas, (b) supersaturated n-hexane vapor with S = 2.7, and (c) supersaturated n-hexane vapor with S = 3.9 Calculations of the Fletcher Diameters for the Heterogeneous Nucleation of Supersaturated Acetonitrile and n-Hexane Vapors on Aluminum Nanoparticles Following the calculations provided on the Supporting Material of Winkler et al (Science 2008, 319, 1474-1377): (Critical cluster size for homogeneous nucleation) (Free energy of the critical cluster in homogeneous nucleation) The ratio of the seed particle radius (Rs) and the critical radius (r*) is given by (note that the critical radius in homogeneous and heterogeneous nucleation is the same): (Free energy of the critical cluster in heterogeneous nucleation) Where: And g and m are given by: Where the contact angle is given by (θ = 2.6 ο) Where the kinetic prefactor K is given by: β is the impingement rate Z is the Zeldovich factor Nads is the surface concentration of adsorbed molecules Where is the vibration frequency of acetonitrile The heterogeneous nucleation probability is given by: Where P is the nucleation probability; N(activated) is the activated clusters with at least r* radius, t is the nucleation period chosen (10-12 s for acetonitrile) The Fletcher radius (RF) is defined @ P=0.5 _ References Wright, D., R Caldwell, C Moxely, and M.S El-Shall, Homogeneous Nucleation in Supersaturated Vapors of Polar Molecules: Acetonitrile, Benzonitrile, Nitromethane, and Nitrobenzene, J Chem Phys 1993, 98, 3356-3368 Kane, D.; Rusyniak, M.; Fisenko, S P and El-Shall, M S Ion Mobility of Pre-Critical Clusters in Supersaturated Vapors: Condensation of Supersaturated Methanol Vapor Induced by Toluene and Styrene ions J Phys Chem 2000, 104, 4912-4919 M Rusyniak, V Abdelsayed, J Campbell, and M S El-Shall, Vapor Phase Homogenous Nucleation of Higher Alkanes: Dodecane, Hexadecane, and Octadecane Critical Supersaturation and Nucleation Rate Measurements, J Phys Chem B 2001, 105 11866-11872 ... P=0.5 _ References Wright, D., R Caldwell, C Moxely, and M.S El-Shall, Homogeneous Nucleation in Supersaturated Vapors of Polar Molecules: Acetonitrile, Benzonitrile,... Nitromethane, and Nitrobenzene, J Chem Phys 1993, 98, 3356-3368 Kane, D.; Rusyniak, M.; Fisenko, S P and El-Shall, M S Ion Mobility of Pre-Critical Clusters in Supersaturated Vapors: Condensation of Supersaturated... and Styrene ions J Phys Chem 2000, 104, 4912-4919 M Rusyniak, V Abdelsayed, J Campbell, and M S El-Shall, Vapor Phase Homogenous Nucleation of Higher Alkanes: Dodecane, Hexadecane, and Octadecane