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Thermal transformations of self-assembled gold glyconanoparticles probed by combined nanocalorimetry and X-ray nanodiffraction Christian Riekel, Emanuela Di Cola, Michael Reynolds, Manfred Burghammer, Martin Rosenthal, David Doblas, and Dimitri A. Ivanov Langmuir, Just Accepted Manuscript • DOI: 10.1021/la504015e • Publication Date (Web): 19 Dec 2014 Downloaded from http://pubs.acs.org on December 23, 2014
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Thermal Transformations of Self-Assembled Gold Glyconanoparticles
probed
by
Combined
Nanocalorimetry and X-Ray Nanobeam Scattering Christian Riekel†*, Emanuela Di Cola†,¶, Michael Reynolds†, Manfred Burghammer†,‡, Martin Rosenthal$, David Doblas&,#, Dimitri A. Ivanov$,& †
European Synchrotron Radiation Facility, B.P.220, Grenoble Cedex, 38043, France
‡
Department of Analytical Chemistry Ghent University Krijgslaan 281, S12B-9000 Ghent, Belgium
$
Faculty of Fundamental Physical and Chemical Engineering, Moscow State University, Moscow, 119991, Russian Federation
&
Institut de Sciences des Matériaux de Mulhouse, CNRS UMR7361, CNRS, 15 rue Jean Starcky, Mulhouse, 68057, France
#
Nanomatériaux pour les Systèmes sous Sollicitations Extrêmes (NS3E), UMR 3208 CNRS/ISL/UDS, French-German Research Institute of Saint-Louis, 5 rue du Général Cassagnou, 68301 Saint Louis, France
¶
Current address: Laboratoire Interdisciplinaire de Physique (LIPhy UMR5588 CNRS/UJF), 140 rue de la Physique, BP87 38402 Saint Martin d'Hères Cedex
KEYWORDS: Gold glyconanoparticles, self-assembly, nanocalorimetry, X-ray nanodiffraction
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ABSTRACT Noble metal nanoparticles with ligand shells are of interest for applications in catalysis, thermoplasmonics and others, involving heating processes. To gain insights into the structure formation processes in such systems, self-assembly of carbohydrate-functionalized gold nanoparticles during precipitation from solution and during further heating up to ca. 340 0C was explored by in-situ combination of nanobeam SAXS/WAXS and nanocalorimetry. Upon precipitation from solution, X-ray scattering reveals the appearance of small 2D domains of close-packed nanoparticles. During heating, increasing interpenetration of the nanoparticle soft shells in the domains is observed up to ca. 81 0C, followed by cluster formation at ca 125 oC, which transform into crystalline gold nuclei around 160 oC. Above ca. 200 oC one observes the onset of coalescence and grain growth resulting in gold crystallites of average size of about 100 nm. The observed microstructural changes are in agreement with the in-situ heat capacity measurements with nanocalorimetry.
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INTRODUCTION Noble metal nanoparticles with ligand shells are of interest for applications such as catalysis,1 thermo-plasmonics,2,
3
and others4,5 involving heating processes. Self-assembly of the
nanoparticles into superstructures may enhance their performance. Probing superstructures corresponds, however, to an analytical challenge.4 Indeed, Transmission Electron Microscopy (TEM) addresses shape and morphological transformations in ultrathin layers and particles.6, 7 Information on stability of ligand shells can be deduced spectroscopically by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) or by thermal analysis techniques such as ThermoGravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC).8 However, the structural information on the nature of the constituent phases, particle sizes and ligand shells of larger functional assemblies, in general cannot obtained by these techniques. In this article, we report on a complementary approach combining nanocalorimetry9, 10
and nanobeam small-angle and wide-angle X-ray scattering (nanoSAXS/WAXS) for probing
thermal transformations of self-assembled colloidal gold nanoparticles (AuNPs) with carbohydrate-functionalized shells in ultra-small volumes. This approach allows simultaneously gaining information on the microstructural evolution including ligand shells and the thermodynamic data. EXPERIMENTAL SECTION Materials. Colloidal gold nanoparticles (AuNPs) with ca. 2.9 nm diameter having a 1.3 ±0.3 nm core functionalized with a ca. 0.8 nm carbohydrate shell were used.11, 12 The extrapolation of gas-phase gold clusters suggests on the average 71 gold atoms per core with a statistical spread from about 30 to 130 gold atoms, in the range of values calculated based on TEM and elemental analysis11, 13 (for more details the reader is referred to Supporting Information). The abbreviation
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“Au71NP” will be used throughout the text to denote these nanoparticles, accordingly. The experiments were performed using a 50 µM Au71NP solution in deionized water corresponding to a particle number density of approximately 3*1016 ml-1. This particle density allows producing bulk residues while AuNP monolayers are generated with typically ~1013 ml-1.14 Nanocalorimetry. The sample was heated using a MEMS-based nanocalorimeter designed for the use with synchrotron radiation (SR) X-ray nanobeams (Figures 1A,B).9 This instrument allows quantitative DC and AC calorimetric measurements over a broad range of heating/cooling rates (≤ 105 K/s) and temperature modulation frequencies (≤ 1 kHz). The electrical heaters assembly provides a rather uniform temperature distribution across the 100x100 µm2 active area on a Si3N4 window. The sample temperature was measured with the help of six thermopiles connected in series, which are assembled on the sensor. In the experiments, in addition to a linear heating rate (10 K min-1), the heating power was modulated using a sinusoidal current with an amplitude of 0.1 mA and a frequency of 37 Hz. The amplitude and phase of the sample temperature versus the modulating signal were computed using real-time Fourier analysis implemented in the controlling software. Sample deposition and heating. The approximately 1 µL droplets of colloidal Au71NP solution were deposited by a pipette on the nanocalorimeter so that its 1 µm thick X-ray transparent Si3N4 window was covered in part by the droplet rim. Drying of the droplet in air resulted within about 10 min in a coffee-ring type residue on the nanocalorimeter Si3N4 chip (Figures 1A,S2B,C) which is also formed on a pure Si3N4 membrane (Figure S2A).15 The residue was subsequently heated from room temperature (r.t.) up to 340oC. After cooling to r.t. the sensor shown in Figure 1A was washed with water, revealing gold nanocrystallites on the window (Figure 1B).
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Synchrotron radiation experiments. A λ=0.08321 nm monochromatic SR-beam was focused down to a ~170 nm spot by refractive lenses with a flux of ~2*109 photons/s at the sample position (Figure S3).16 NanoSAXS/WAXS was performed in transmission geometry with the beam normal to the sample on the substrate (Figure S3). 1D- or 2D raster-scans of the sample through the beam were performed by a PI hexapod or piezo-stage. At each raster-step a scattering pattern was collected by a CCD camera with X-ray converter screen and 2Kx2K pixels of 50x50 µm2 each. Radiation damage was revealed by an increase of SAXS background within about 2s irradiation. Exposure times were therefore limited to 0.5 s/raster-point. The diffraction patterns were analyzed using the FIT2D software.17 Results are displayed as raster-scan diffraction images (RD-image) with “pixels” corresponding to individual patterns.18 WAXS data simulations were performed by the Materials Studio 6.1 Powder Diffraction module (Accelrys Software Inc.) assuming a particle size of 200 nm. The SAXS data were analyzed and fitted by the SAXSutilities package.19 (Supporting Information) RESULTS AND DISCUSSION A RD-image from the residue on the Si3N4 window at r.t. reveals SAXS powder rings corresponding to a d-spacing of ~2.62 nm and a weak diffuse feature at larger angles covering a range of ~0.2< d (nm)
