Colloid Particles Studied by Near Edge X-ray. Absorption Spectronanoscopy

Transcription

1 Supporting Information for: Individual Hybrid Colloid Particles Studied by Near Edge X-ray Absorption Spectronanoscopy Katja Henzler 1,2* ; Peter Guttmann 1, Yan Lu 2, Frank Polzer 3, Gerd Schneider 1, Matthias Ballauff 2,3 1 Institute for Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Albert-Einstein-Str. 15 D Berlin, Germany 2 Institute for Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, D Berlin, Germany 3 Department of Physics, Humboldt University Berlin, Newtonstr. 15, D Berlin Germany Corresponding Author: Katja Henzler; katja.henzler@helmholtz-berlin.de S 1

2 METHODS Materials All chemical substances used in this study were of analytical grade and used without further purification. For the production of ultrapure water we used an Integral 10 device (Millipore; resistivity 18.2 MΩ cm). Synthesis of the thermosensitive core-shell microgel particles The synthesis of the thermosensitive core-shell particles (PS-PNIPAM) was modified from the previous report. 1 In a first step, a polystyrene (PS) core covered with a thin layer of copolymerized poly(n-isopropylacrylamide) (PNIPAM) was prepared by conventional emulsion polymerization. The seed latex was prepared by using styrene (30.00 g) and N- Isopropylacrylamide (NIPAM; 1.63 g) as monomers, sodium dodecyl sulfate (SDS; 0.30 g dissolved in 200 g water) as surfactant and potassium persulfate (KPS; 0.30 g dissolved in 20 g of water) as initiator. The reaction was run at 80 C for 8 h in N 2 atmosphere. The core particles were purified via serum replacement against the tenfold volume of water. The hydrodynamic radius of the PS core was determined with dynamic light scattering to 90 nm at 25 C. The PS-NIPA core-shell system was prepared by seeded emulsion polymerization. PS core latex (7.67 g) was diluted with 240 g of water together with 8.37 g of NIPAM and 0.29 g of N,N -Methylenebis(acrylamide) (BIS). After that the mixture was heated to 80 C. By the addition of 0.30 g of KPS (dissolved in 10 g of water) the reaction was started, and continued for 4.5 h. The latex was purified by serum replacement against deionized water (membrane: S 2

3 cellulose nitrate with 100 nm pore size supplied by Schleicher & Schuell). The hydrodynamic radius of the core-shell microgel was measured with dynamic light scattering to 228 nm at 25 C. Synthesis of TiO 2 nanoparticles embedded into microgel A semi-batch process has been made for the synthesis of TiO 2 nanoparticles in the PNIPAM microgel g of NPS-PNIPAM microgel particles solution (1.77 wt.-% solid content) was diluted in 68 g ethanol. A water amount of 0.4 ml added under stirring. The reaction was initiated by adding the solution of 0.4 ml titanium (IV) ethoxide (Ti(OEt) 4 ) dissolved in 12 ml ethanol. Ti(OEt) 4 solution was added drop wise at a feeding rate of 0.08 ml/min. The reaction mixture was vigorously stirred for two more hours after the addition of Ti(OEt) 4 solution. The TiO 2 alcosols were then washed with ethanol and water by repeated centrifugation 3 times and redispersed into water after cleaning. NEXAFS-TXM measurement Sample preparation for cryo-neaxafs-txm: Custom designed gold grids (specified as HZB-2) were purchased by Glider Grids, Grantham, United Kingdom. The Grids are coated with a R2/2-perforated carbon foil by Quantumfoil Micro Tools, Jena, Germany. The carbon coated grids have been pretreated by glow discharge for 10 s. Approximately 5 µl sample dispersion containing approx. 1 wt-% TiO 2 hybrid particles and 0.5wt-% anatase reference material was placed on the TXM grid. The liquid was blotted with a filter paper after 30 s. The grid was plunged directly into liquid ethane for verification. The NEXAFS-TXM Ti L 2,3 -edge spectra were recorded with the TXM which is installed at the undulator beamline U41-FSGM at BESSY II, Berlin. It provides a high spatial resolution close to S 3

4 10 nm (half-pitch) and a spectral resolution up to E/ E In the full-field experimental configuration the data of many isolated particles are simultaneously recorded, thereby containing already statistical information. Typical spectra are presented for each set of measurements. Up to 125 particles were analyzed to verify the reproducibility of the results. The TXM allows measurements to be taken at room or liquid nitrogen temperature in a vacuum of bar. The spectra were recorded at liquid nitrogen temperature in transmission mode by taking a sequence of images over a range of photon energies covering the investigated absorption edges with E/ E > Note that the exit slit of the monochromator was set at 5 µm and the exposure time for one image with pixels is set between 6 to 8 s to achieve a sufficient spectral resolution and control of the radiation doses. Taking an image stack with 219 images at different energies needs inherently about 80 to 120 min because of all necessary movements, camera read out time and image storage. The NEXAFS spectra were normalized since the photon flux varies as a function of photon energy (hν) and time in the object field (x, y). The normalization was performed by dividing the function I(x, y, hν) recorded on a single nanostructure by the photon flux curve I 0 (x+ x, y+ y, hν) recorded in its sample free proximity at position (x+ x, y+ y). Both I(x, y, hν) and I 0 (x, y, hν) were recorded on the same image stack since bare region in the vicinity of each nanostructures permit the measurement of I 0. Cryogenic TEM TEM specimens were vitrified by plunging the samples into liquid ethane using an automated plunge freezer (Vitrobot Mark IV, FEI Deutschland GmbH, Frankfurt a. M., Germany). The carbon coated copper grids have been pretreated by 10 s of glow discharge. Approximately 5 µl of a 1 wt% solution on a TEM copper grid with lacey carbon support film (200 meshes, Science S 4

5 Services, Munich, Germany). The liquid was blotted with a filter paper after 30 s applying a blot force of 0 for 1 s. No wait time or drain time have been used. The specimen was inserted into a pre-cooled cryo transfer sample holder (914, Gatan, Eching, Germany) and transferred into a JEOL JEM-2100 with a LaB6 cathode (JEOL GmbH, Eching, Germany). The TEM was operated at an acceleration voltage of 200 kv. All images were recorded digitally by a bottommounted 4k 4k CMOS camera system using low dose conditions (TemCam-F416, TVIPS, Gauting, Germany) and processed with a digital imaging processing system (EM-Menu 4.0, TVIPS, Gauting, Germany). All further TEM measurements were conducted with the same instrumentation. Bright field TEM and Selected Area Electron Diffraction (SAED) TEM specimens were prepared by putting approximately 5 µl of a 0.1 wt% solution on a TEM copper grid with carbon support film (200 meshes, Science Services, Munich, Germany). The carbon coated copper grids have been pretreated by glow discharge 10 s. The excess of liquid was blotted with a filter paper after 2 min. The remaining liquid film on the TEM grid was dried at room temperature for at least one hour. The specimen was inserted into the sample holder (EM21010, JEOL GmbH, Eching, Germany) and transferred to a JEOL JEM-2100 with a LaB6 cathode (JEOL GmbH, Eching, Germany). The TEM was operated at an acceleration voltage of 200 kv. All images were recorded digitally by a bottom-mounted 4k 4k CMOS camera system (TemCam-F416, TVIPS, Gauting, Germany) and processed with a digital imaging processing system (EM-Menu 4.0, TVIPS, Gauting, Germany). Selected area electron diffraction patterns were recorded using a camera length of 60 cm and a 20 µm selected area electron diffraction aperture. The instrument was calibrated just before the S 5

6 actual measurement using SAED patterns of an evaporated aluminum film on a 3.05 mm TEM grid (Science Services, Munich, Germany). All patterns were recorded digitally by a bottommounted 4k 4k CMOS camera system (TemCam-F416, TVIPS, Gauting, Germany) and processed with a digital imaging processing system (EM-Menu 4.0, TVIPS, Gauting, Germany). S 6

7 ADDITIONAL TEM-IMAGES AND ANALYSIS Figure S1 shows a cryo-tem micrograph of a colloidal hybrid particle. The PNIPAM shell remains swollen due to the vitrification of the surrounding water. Therefore, we get a good contrast between the TiO 2 nanoparticles ant the PNIPAM-shell. The majority of the generated TiO 2 nanoparticles are embedded into the inner part of the microgel shell. Only a few nanoparticles are bound at the water/pnipam-interface. The dotted line in Figure S1 represents the hydrodynamic radius of the microgel at room temperature. However, these nanoparticles at the water/pnipam-interface must bind strongly to the PNIPAM because they cannot be washed away by ultrafiltration. Figure S1: Cryo-TEM image of a colloidal hybrid particle in false color representation. The PNIPAM network remains in the swollen state by the surrounding vitrified water. The whit dotted line represents the hydrodynamic radius of the microgel measured by dynamic light scattering at room temperature. The TiO 2 nanoparticles are distributed in the microgel layer. S 7

8 Figure S2 shows TEM micrographs in false color representation of four hybrid particles. From these micrographs the size of the TiO 2 nanoparticles is measured and subsequently the size distribution analysed (HR-TEM particle 1: 20 TiO 2 nanoparticles; cryo-tem particle 2: 100 TiO 2 nanoparticles; cryo-tem particle 3: 100 TiO 2 nanoparticles; cryo-tem particle 4: 106 TiO 2 nanoparticles). The diagram in Figure S2 shows the obtained size distribution of the TiO 2 nanoparticles on the four microgel particles. The determined TiO 2 nanoparticles size distributions on the analyzed microgel particles are similar within the errors. Therefore, it can be concluded that the size distribution of the TiO 2 nanoparticles will be very similar on all carrier particles. The size distribution can be well described by a log-normal-distribution function. S 8

9 Figure S2: Determined size distribution of the TiO 2 nanoparticles on four individual microgel particles shown in the TEM micrographs. The size distribution can be well described by a lognormal-distribution. S 9

10 In the dried state of the composite particles, the crystallinity of the TiO 2 nanoparticles can be examined by high resolution transmission electron microscopy (HR-TEM). The crystal planes of the TiO 2 nanoparticles can be clearly seen in Figure S3 (a) (especially in the magnified insets 1-4). Therefore, crystalline TiO 2 nanoparticles have been generated at room temperature in the PNIPAM-shell without any additional heat treatment. The lattice fringes with a spacing of nm correspond to (011) planes of an anatase crystal structure. Moreover, the diffraction pattern of the selected-area electron diffraction (SAED) in Figure S3 (b) depicts clearly the crystalline structure of the generated TiO 2 nanoparticles. The diffraction rings of the SAED can be assigned to an anatase crystal structure. Figure S3: (a) High resolution-tem micrograph of the dried composite material. The lattice planes of the TiO 2 nanoparticles can be resolved (Inset 1 to 4; insets scale bar equals 5 nm). (b) The SAED pattern shows the sequence of diffraction rings which is consistent for an anatase crystal structure of the TiO 2 nanoparticles. S 10

11 References: 1. Seelenmeyer, S.; Deike, I.; Rosenfeldt, S.; Norhausen, C.; Dingenouts, N.; Ballauff, M.; Narayanan, T.; Lindner, P. J. Chem. Phys. 2001, 114, Lu, Y.; Hoffmann, M.; Yelamanchili, R. S.; Terrenoire, A.; Schrinner, M.; Drechsler, M.; Moller, M. W.; Breu, J.; Ballauff, M. Macromol. Chem. Phys. 2009, 210, S 11